Thirty years of density functional theory in computational chemistry: an overview and extensive assessment of 200 density functionals

Supramolecular assembly strategy of modified starch chains for achieving recyclable emulsion biocatalysis within a narrow pH range

Stimuli-responsive Pickering emulsions are promising in biocatalysis for their ease of product separation and emulsifier recovery. However, pH responsiveness, though simple and cost-effective, faces challenges in precise control and narrow transition ranges, limiting its use in enzymatic catalysis. Herein we introduced amorphous octenyl succinic anhydride-modified debranched starch chains (Am-OSA-St) to control emulsion properties within a pH range suitable for enzymatic catalysis. By adjusting the OSA group density and molecular weight, Am-OSA-St allowed emulsions to transition reversibly between pH 7.3 and 5.5 and enabled self-recycling through supramolecular self-assembly. Employing molecular dynamics simulations and physicochemical characterization, we elucidated the control mechanism of oil-water interfaces via the microstructure transformation of Am-OSA-St. The findings revealed that protonation of carboxylate groups disrupted the charge balance and polarity of starch chains, leading to strong electrostatic and van der Waals interactions that drove self-assembly. This entanglement caused starch chains in the aqueous phase to "drag" those at the oil-water interface, moving them into the aqueous phase and forming micelles. These micelles, with a hydrophobic interior and hydrophilic exterior, prevented re-adsorption. Testing with Candida antarctica Lipase B (CALB) and N-acetylneuraminic lyase showed that the pH-regulated emulsion system maintained excellent efficiency and cycling stability in mild conditions.

Canonical coupled cluster binding benchmark for nanoscale noncovalent complexes at the hundred-atom scale

In this study, we introduce two datasets for nanoscale noncovalent binding, featuring complexes at the hundred-atom scale, benchmarked using coupled cluster with single, double, and perturbative triple [CCSD(T)] excitations extrapolated to the complete basis set (CBS) limit. The first dataset, L14, comprises 14 complexes with canonical CCSD(T)/CBS benchmarks, extending the applicability of CCSD(T)/CBS binding benchmarks to systems as large as 113 atoms. The second dataset, vL11, consists of 11 even larger complexes, evaluated using the local CCSD(T)/CBS method with stringent thresholds, covering systems up to 174 atoms. We compare binding energies obtained from local CCSD(T) and fixed-node diffusion Monte Carlo (FN-DMC), which have previously shown discrepancies exceeding the chemical accuracy threshold of 1 kcal/mol in large complexes, with the new canonical CCSD(T)/CBS results. While local CCSD(T)/CBS agrees with canonical CCSD(T)/CBS within binding uncertainties, FN-DMC consistently underestimates binding energies in π-π complexes by over 1 kcal/mol. Potential sources of error in canonical CCSD(T)/CBS are discussed, and we argue that the observed discrepancies are unlikely to originate from CCSD(T) itself. Instead, the fixed-node approximation in FN-DMC warrants further investigation to elucidate these binding discrepancies. Using these datasets as reference, we evaluate the performance of various electronic structure methods, semi-empirical approaches, and machine learning potentials for nanoscale complexes. Based on computational accuracy and stability across system sizes, we recommend MP2+aiD(CCD), PBE0+D4, and ωB97X-3c as reliable methods for investigating noncovalent interactions in nanoscale complexes, maintaining their promising performance observed in smaller systems.

A General and Transferable Local Hybrid Functional for Electronic Structure Theory and Many-Fermion Approaches

Density functional theory has become the workhorse of quantum physics, chemistry, and materials science. Within these fields, a broad range of applications needs to be covered. These applications range from solids to molecular systems, from organic to inorganic chemistry, or even from electrons to other Fermions, such as protons or muons. This is emphasized by the plethora of density functional approximations that have been developed for various cases. In this work, two new local hybrid exchange-correlation density functionals are constructed from first-principles, promoting generality and transferability. We show that constraint satisfaction can be achieved even for admixtures with full exact exchange, without sacrificing accuracy. The performance of the new functionals CHYF-PBE and CHYF-B95 is assessed for thermochemical properties, excitation energies, Mössbauer isomer shifts, NMR spin-spin coupling constants, NMR shieldings and shifts, magnetizabilities, and EPR hyperfine coupling constants. Here, the new density functional shows excellent performance throughout all tests and is numerically robust only requiring small grids for converged results. Additionally, both functionals can easily be generalized to arbitrary Fermions as shown for electron-proton correlation energies. Therefore, we outline that density functionals generated in this way are general purpose tools for quantum mechanical studies.

Informing Empirically Fitted Density Functionals about the Physics of Interelectronic Interactions

Further progress in constructing highly accurate density functionals by enforcing known laws of interelectron interactions is slow, so fitting techniques are usually employed nowadays. These approaches were shown to lead to overfitting when a functional becomes unreliable for properties on which it was not trained on. An approach to maintain the correct physical behavior of a functional during its training is required to build more complex and accurate functionals, including those based on neural networks. We devise such an approach and apply it to reparameterize the heavily fitted and popular M06-2X functional on its original training set. The resulting physics-informed functionals piM06-2X and piM06-2X-DL approached the accuracy of M06-2X in thermochemical tasks and the accuracy of PBE0 in electron densities, taking the best out of both worlds. Surprisingly, we find that a very similar performance can be achieved directly by using the PBE-2X functional without any fitting. The proposed approach should be indispensable for training future neural-network-based functionals.

Assessing Computational Methods to Calculate the Binding Energies of Dimers of Five-Membered Heterocyclic Molecules

Computational electronic structure methods, including ab initio and density functional theory (DFT), have been assessed in calculating the binding energies of 14 five-membered heterocyclic dimers. The configurations were generated using classical molecular dynamics before optimization at the MP2/aug-cc-pVTZ. Benchmark binding energies are calculated at the CCSD(T)/CBS level of theory. Among the ab initio methods, the DLPNO-CCSD(T)/CBS method has the best performance, reproducing CCSD(T)/CBS with a mean absolute deviation (MAD) of 0.17 kcal/mol. In addition, a schematic CCSD(T)/CBS approach perfectly reproduces the canonical CCSD(T)/CBS with a mean absolute error of 0.08 kcal/mol. Regarding DFT functionals, it has been found that counterpoise corrections have negligible effects on the accuracy of the functionals. Furthermore, including the D3 empirical dispersion considerably enhances the accuracy of the DFT functionals. As a result, outstanding performance is noted for the double hybrid functional B2K-PLYP, with a mean absolute error of 0.25 kcal/mol. In addition to the B2K-PLYP double hybrid functional, M05-D3, B97D, M05-2X-D3, M05-2X, M06-HF, M08-HX, M11, TPSSh-D3, and RSX-0DH-D3(BJ) have MAD values lower than 0.5 kcal/mol. These functionals are recommended for further investigations of five-membered heterocyclic clusters.

A Benchmark Study of DFT-Computed p-Block Element Lewis Pair Formation Enthalpies Against Experimental Calorimetric Data

The quantification of Lewis acidity is of fundamental and applied importance in chemistry. While the computed fluoride ion affinity (FIA) is the most widely accepted thermodynamic metric, only sparse experimental values exist. Accordingly, a benchmark of methods for computing Lewis pair formation enthalpies, also with a broader set of Lewis bases against experimental data, is missing. Herein, we evaluate different density functionals against a set of 112 experimentally determined Lewis acid/base binding enthalpies and gauge influences such as solvation correction in structure optimization. From that, we can recommend r2SCAN-3c for robust quantification of this omnipresent interaction.

Spectroscopic Insight on Neodymium Solvation in Lithium Borohydride-Supported Electrolyte

Borohydride-based electrolytes have recently emerged as promising media for the electrodeposition of electropositive metals, including rare earth (RE) elements. While the presence of supporting alkali metal cations and RE counteranions provides essential electrochemical conductivity for achieving fast metal electrodeposition, interactions between the host ligand and solvated neodymium (Nd) complexes remain unclear. This study provides insights into the coordination structure of a concentrated and directly solvated Nd salt in a lithium borohydride-supported electrolyte. Our spectroscopic results indicate that the RE coordination environment is significantly influenced by the solvation mechanism, which can vary between metathesis and complexation pathways, primarily dictated by stoichiometric factors. Under dilute conditions, nearly complete metathesis of anions leads to a high coordination number for the host ligand (borohydride), consistent with the previously reported solvated Nd speciation in chlorine-free electrolytes. In contrast, concentrated dissolution of the Nd salt in the supported electrolyte is dominated by a complexation pathway featuring a Li-ion-paired complex with a low coordination number of the host ligand. Density functional theory (DFT) calculations indicated that the observed blue shift in the borohydride vibration was the result of an increase in electron density drawn into the terminal B-H interbond region from the hydride as the coordination changed from Li to Nd. In conjunction with DFT results, vibrational analyses allowed correlation of the experimental shifts associated with changes in Nd ligation and coordination spheres, further consolidating the prevalence of highly chloride-coordinated species under concentrated conditions. The outcomes of this work illuminate the distinctive and heterogeneous coordination structures that the electroactive RE species can adopt at high concentrations in lithium borohydride-supported electrolytes, as a key step to comprehend the reported metal electrodeposition performance in these media.

Acceleration without Disruption: DFT Software as a Service

Density functional theory (DFT) has been a cornerstone in computational chemistry, physics, and materials science for decades, benefiting from advancements in computational power and theoretical methods. This paper introduces a novel, cloud-native application, Accelerated DFT, which offers an order of magnitude acceleration in DFT simulations. By integrating state-of-the-art cloud infrastructure and redesigning algorithms for graphic processing units (GPUs), Accelerated DFT achieves high-speed calculations without sacrificing accuracy. It provides a user-friendly and scalable solution for the increasing demands of DFT calculations in scientific communities. The implementation details, examples, and benchmark results illustrate how Accelerated DFT can significantly expedite scientific discovery across various domains.

Data Quality in the Fitting of Approximate Models: A Computational Chemistry Perspective

Empirical parametrization underpins many scientific methodologies including certain quantum-chemistry protocols [e.g., density functional theory (DFT), machine-learning (ML) models]. In some cases, the fitting requires a large amount of data, necessitating the use of data obtained using low-cost, and thus low-quality, means. Here we examine the effect of using low-quality data on the resulting method in the context of DFT methods. We use multiple G2/97 data sets of different qualities to fit the DFT-type methods. Encouragingly, this fitting can tolerate a relatively large proportion of low-quality fitting data, which may be attributed to the physical foundations of the DFT models and the use of a modest number of parameters. Further examination using "ML-quality" data shows that adding a large amount of low-quality data to a small number of high-quality ones may not offer tangible benefits. On the other hand, when the high-quality data is limited in scope, diversification by a modest amount of low-quality data improves the performance. Quantitatively, for parametrizing DFT (and perhaps also quantum-chemistry ML models), caution should be taken when more than 50% of the fitting set contains questionable data, and that the average error of the full set is more than 20 kJ mol-1. One may also follow the recently proposed transferability principles to ensure diversity in the fitting set.

Delocalization error poisons the density-functional many-body expansion

The many-body expansion is a fragment-based approach to large-scale quantum chemistry that partitions a single monolithic calculation into manageable subsystems. This technique is increasingly being used as a basis for fitting classical force fields to electronic structure data, especially for water and aqueous ions, and for machine learning. Here, we show that the many-body expansion based on semilocal density functional theory affords wild oscillations and runaway error accumulation for ion-water interactions, typified by F-(H2O) N with N ≳ 15. We attribute these oscillations to self-interaction error in the density-functional approximation. The effect is minor or negligible in small water clusters, explaining why it has not been noticed previously, but grows to catastrophic proportion in clusters that are only moderately larger. This behavior can be counteracted with hybrid functionals but only if the fraction of exact exchange is ≳50%, whereas modern meta-generalized gradient approximations including ωB97X-V, SCAN, and SCAN0 are insufficient to eliminate divergent behavior. Other mitigation strategies including counterpoise correction, density correction (i.e., exchange-correlation functionals evaluated atop Hartree-Fock densities), and dielectric continuum boundary conditions do little to curtail the problematic oscillations. In contrast, energy-based screening to cull unimportant subsystems can successfully forestall divergent behavior. These results suggest that extreme caution is warranted when the many-body expansion is combined with density functional theory.

Disclosing novel melanogenesis pathways: Formation of unexpected biphenyl-type dimers through radical-radical coupling by solid-state oxidation of the melanin biosynthetic precursor 5,6-dihydroxyindole

Investigation of the oxidation pathway of 5,6-dihydroxyindole (DHI), one of the main biosynthetic precursors of the brown-to-black skin and hair melanin pigments, represents a promising approach for the elucidation of the structure of these pigments in biological systems. We report herein the exploration of DHI oxidation chemistry under conditions so far poorly investigated, i.e. solid-state mechanochemical conditions, mimicking those that could be found in vivo in melanosomes, where melanin growth takes place in a confined space on a solid proteinaceous matrix, that allowed for the isolation and characterization of new dimers. Mechanistic experiments allowed to propose radical-radical coupling as the main dimerization pathway under solid-state conditions preventing ionic polymerization of the 5,6-dihydroxyindole system, indicating that the oxidation chemistry of this melanogenic precursor strongly depends on the reaction environment. The relevance for melanogenesis of the DHI oxidation pathway, disclosed herein, was also demonstrated by ad hoc experiments in which the solid-state reaction was carried out in the presence of proteins. Finally, the chromophores of the species generated by oxidation of the new dimers were investigated with a view to expanding the knowledge on the functional properties of melanin pigments, including mainly photoprotection.

Stability of [10-12]cycloparaphenylene complexes with pristine fullerenes C76,78,84 and endohedral metallofullerenes M3N@C78,80

[n]Cycloparaphenylenes ([n]CPPs) are strained macrocycles, comprising only sp2-hybridized carbon atoms. In recent years, [n]CPPs have become of great research interest in the field of supramolecular chemistry since their special structure enables the formation of novel host-guest complexes. In this work, we investigate the gas-phase chemistry of noncovalent complexes of [10-12]CPP with the pristine fullerenes C76/78/84 and the endohedral metallofullerenes (EMFs) Sc3N@D3h-C78, Sc3N@D5h-C80 and M3N@Ih-C80 (M = Sc, Y, Lu, Gd). The [1 : 1] complexes with [10-12]CPP are detected as radical cations. The stability and charge distributions of these complexes are studied using energy-resolved collision-induced dissociation (ER-CID). Our results assess the size complementarity, the influence of fullerene symmetry and size as well as the role of the metal size inside the EMF on the binding affinity and complex stability. Two main trends in complex stability have been found: First, [10-12]CPP form more stable complexes with EMFs than with pristine fullerenes and second, all complexes of EMFs with the C80 skeleton show similar stability despite the different metal clusters encapsulated. Another major finding is the fact that [11]CPP is generally the most suitable host for fullerenes with a C76/78/80/84 skeleton. Considering the charge distributions, we observe the existence of two different fragmentation channels for complexes with EMFs where the radical cation is either located at the CPP or at the EMF: (1) [n]CPP+˙ + EMF and (2) [n]CPP + EMF+˙. This behavior allows a clear distinction of the cage isomers ([11]CPP⊃Sc3N@Ih-C80)+˙ and ([11]CPP⊃Sc3N@D5h-C80)+˙ in the MS2 experiment. The experimental results are accompanied by density functional theory (DFT) calculations of ionization potentials (IPs) and fragmentation energies. The computational results fully confirm the measured order of complex stabilities and explain the prevalence of EMF or CPP signals in the spectra by the trend in ionization potentials.

Catching the π-Stacks: Prediction of Aggregate Structures of Porphyrin

π-π interactions decisively shape the supramolecular structure and functionality of π-conjugated molecular semiconductor materials. Despite the customizable molecular building blocks, predicting their supramolecular structure remains a challenge. Traditionally, force field methods have been used due to the complexity of these structures, but advances in computational power have enabled ab initio approaches such as density functional theory (DFT). DFT is particularly suitable for finding energetically favorable structures of dye aggregates, which are determined by a large number of different interactions, but a systematic aggregate search can still be very challenging due to the large number of possible geometries. In this work, we show ways to overcome this challenge. We investigate how finely translational and rotational lattices must be structured to identify all energetic minima of π-stack structures, focusing on porphyrins as a prototype challenge. Our approach involves single-point DFT calculations of systematically varied dimer geometries, identification of local energy minima, hierarchical grouping of geometrically similar structures, and optimization of the energetically favorable representatives of each geometric family. This ab initio method provides a general framework for the systematic prediction of aggregate structures and reveals geometrically diverse and energetically favorable dimers.

Enhanced quantum efficiency of dicyano BODIPYs over difluoro BODIPYs: A DFT approach

The modified BODIPY (pyrromethene) dyes with cyano (-CN), substituting usual fluorine (-F), at the 4-position may give enhanced photochemical stability and quantum yield of fluorescence (QYF) when compared to the corresponding fluoro derivative. We have investigated and discussed comparatively the structural parameters of the ground (S0) and excited (S1) state geometries of a few widely used BODIPY dyes, both 4-cyano and 4-fluoro pyrromethene (PM), through DFT and TD-DFT studies and established the reasons for improved QYF of the cyano derivatives. The electrophilicity index indicates the stability of the excited geometry of the cyanated BODIPY and the calculated transition dipole moments reveal a longer lifetime of the excited state (S1) for the cyano BODIPY. The higher singlet and triplet gap in cyanated BODIPY accounts for higher QYF due to restricted transition from singlet to triplet state. This suggests that a population inversion, crucial for laser action, is easier to build up for cyano derivative than for the commonly used fluoro analogue while other gain/loss parameters of the PM dye lasers remain similar. Hence, 4-cyano derivatives of the PM dyes may be useful for more efficient lasing applications. The non-linear optical properties of the PM dyes are also investigated.

Promoting Apoptosis in MCF-7 Cells via ROS Generation by Quinolino-triazoles Derived from One-Pot Telescopic Synthesis

Inhibition of vascular endothelial growth factor receptor 2 (VEGFR-2) facilitates potent antiangiogenic and anticancer responses. In this regard, the development of effective pharmacophores, i.e., quinoline-based triazole derivatives 6a-j, by a one-pot telescopic approach is our focus. Among all of them, 6f, possessing amide and cyanide substituents, displayed the highest binding ability with VEGFR-2, having high affinity of -8.9 kcal/mol. Further, 6f and 6g (containing amide and bromo groups) exhibited a wide spectrum of anticancer activities due to the presence of active oxidative stress inducers, with cytotoxicity values of 10 ± 0.2 and 12 ± 0.6 μM, respectively. Apoptosis analysis demonstrated the involvement of 6f and 6g in mitochondrial damage and the loss of mitochondrial membrane potential (ΔΨm). Intercellular localization of 6f/6g in MCF-7 revealed the presence of 6g in the cytoplasm along with an increase in ROS production and a reduction in MMP, proving the ability of 6g to target mitochondria.

The Paradox of Global Multireference Diagnostics

Modern computational chemistry methods are a useful tool for modeling many chemical systems, but they are challenged by multireference species (e.g., transition metals). A variety of diagnostics have been formulated to identify such cases. They are typically developed by analyzing multireference characters of small molecules, and many provide an average picture of the entire system. We caution the use of such diagnostics for large systems because large systems may include parts with varying degrees of multireference characters. Specifically, a small but highly multireference component may yield a large error in absolute terms, which may be masked in an average value over the entire molecule. As the calculation of molecular relative energies often concerns errors in absolute terms, such a false sense of safety may be detrimental. A prospective means to tackle this challenge is to use fractional occupation density to identify potentially problematic components in a system and then examine this moiety with higher-level computations on appropriately constructed smaller models.

"Best" Iterative Coupled-Cluster Triples Model? More Evidence for 3CC

To follow up on the unexpectedly good performance of several coupled-cluster models with approximate inclusion of 3-body clusters [Rishi, V.; Valeev, E. F. J. Chem. Phys. 2019, 151, 064102.] we performed a more complete assessment of the 3CC method [Feller, D. . J. Chem. Phys. 2008, 129, 204105.] for accurate computational thermochemistry in the standard HEAT framework. New spin-integrated implementation of the 3CC method applicable to closed- and open-shell systems utilizes a new automated toolchain for derivation, optimization, and evaluation of operator algebra in many-body electronic structure. We found that with a double-ζ basis set the 3CC correlation energies and their atomization energy contributions are almost always more accurate (with respect to the CCSDTQ reference) than the CCSDT model as well as the standard CCSD(T) model. The mean absolute errors in cc-pVDZ {3CC, CCSDT, and CCSD(T)} electronic (per valence electron) and atomization energies relative to the CCSDTQ reference for the HEAT data set [Tajti, A. . J. Chem. Phys. 2004, 121, 11599-11613.], were {24, 70, 122} μEh/e and {0.46, 2.00, 2.58} kJ/mol, respectively. The mean absolute errors in the complete-basis-set limit {3CC, CCSDT, and CCSD(T)} atomization energies relative to the HEAT model reference, were {0.52, 2.00, and 1.07} kJ/mol, The significant and systematic reduction of the error by the 3CC method and its lower cost than CCSDT suggests it as a viable candidate for post-CCSD(T) thermochemistry applications, as well as the preferred alternative to CCSDT in general.

Smoother Semiclassical Dispersion for Density Functional Theory via D3S: Understanding and Addressing Unphysical Minima in the D3 Dispersion Correction Model

One of the most widely used and computationally efficient models that accounts for London dispersion interactions within density functional theory (DFT) is the D3 dispersion correction model. In this work, we demonstrate that this model can induce the appearance of unphysical minima on the potential energy surface (PES) when the coordination number of atoms changes. Optimizing to these artifactual structures can lead to significant errors in determining the interaction energy between two molecules and in estimating the thermodynamic properties of the system. In several specific examples, such as Kuratowski-type H2-NiKur and H2-PdKur clusters, these local minima exhibited extremely high PES curvature, resulting in incorrect estimations of harmonic frequencies and significant overestimations of zero-point energy and enthalpy values. Although such erroneous behavior of the D3 model is relatively rare, it can occur across a wide range of chemical species, including molecules like the [Li(C6H6)]+ complex and the dispiro(acridan)-substituted pyracene (DSAP) molecule. Our analysis reveals that the root of the problem lies in the definition of the AB atomic-pair dependent C6AB coefficients in the D3 model. To address this issue, we propose a reparameterization of the D3 model by introducing a modified C6AB functional form that now depends on the specific pair of considered atoms. This new model, termed D3-Smooth (or D3S for short), is designed to smooth out the PES associated with the dispersion correction. By doing so, we demonstrate that D3S eliminates unphysical local minima while maintaining the quite satisfactory accuracy of the parent D3 method in interaction energy benchmark sets. For example, the RMS difference between using the D3(BJ) correction to B3LYP and the D3S(BJ) correction across the large MGCDB84 data set of nearly 5000 data points is only 0.12 kJ/mol. Similar results are obtained for every other D3-corrected functional tested. Consistent with this result, no significant improvement could be obtained for the B3LYP-D3S(0) correction by reoptimizing the damping function.

An Efficient RI-MP2 Algorithm for Distributed Many-GPU Architectures

Second-order Møller-Plesset perturbation theory (MP2) using the Resolution of the Identity approximation (RI-MP2) is a widely used method for computing molecular energies beyond the Hartree-Fock mean-field approximation. However, its high computational cost and lack of efficient algorithms for modern supercomputing architectures limit its applicability to large molecules. In this paper, we present the first distributed-memory many-GPU RI-MP2 algorithm explicitly designed to utilize hundreds of GPU accelerators for every step of the computation. Our novel algorithm achieves near-peak performance on GPU-based supercomputers through the development of a distributed memory algorithm for forming RI-MP2 intermediate tensors with zero internode communication, except for a single O ( N 2 ) asynchronous broadcast, and a distributed memory algorithm for the O ( N 5 ) energy reduction step, capable of sustaining near-peak performance on clusters with several hundred GPUs. Comparative analysis shows our implementation outperforms state-of-the-art quantum chemistry software by over 3.5 times in speed while achieving an 8-fold reduction in computational power consumption. Benchmarking on the Perlmutter supercomputer, our algorithm achieves 11.8 PFLOP/s (83% of peak performance) performing and the RI-MP2 energy calculation on a 314-water cluster with 7850 primary and 30,144 auxiliary basis functions in 4 min on 180 nodes and 720 A100 GPUs. This performance represents a substantial improvement over traditional CPU-based methods, demonstrating significant time-to-solution and power consumption benefits of leveraging modern GPU-accelerated computing environments for quantum chemistry calculations.

Assessment of the usefulness of β-cyclodextrin in the removal of progesterone from the environment

The paper presents the results and interpretation of theoretical calculations for the progesterone-β-cyclodextrin (P@β-CD; G4MP2) and progesterone-β-cyclodextrin-β-cyclodextrin (P@β-CD-β-CD; G2) systems. The geometry of the progesterone molecule was optimized on basis of the DFT theory using the B3LYP, PBE1PBE and M06-2X functionals, for selected Pople basis sets [6-31G, 6-31++G, 6-31++G(d,p), 6-311G, 6-311++G, 6-311++G(d,p)] and the Dunning basis set (aug-cc-pVDZ). Presented results of theoretical calculations provide insight into the mechanism of formation of supramolecular systems of progesterone and β-cyclodextrin, allowing us to understand the impact of differences in the polarizability of specific fragments of the "guest" molecule, through the analysis of the Mulliken population distribution, on the tendency for equilibrium inclusion by "host" molecules characterized by selective affinity towards hydrophilic and hydrophobic molecular systems. The comparison of model structures of "guest-host" systems with 1:1 and 1:2 stoichiometry allows us to assess the contribution of a given type of non-covalent interactions (hydrogen bonds, van der Waals interactions, London dispersion forces) in the formation of supramolecular complexes. Due to the complexity of the real research object, including interactions between large molecules in solution, in this work it was decided to choose an approximation that reflects only the key effects. The results presented in this paper constitute a starting point for both theoretical research on analogous supramolecular systems based on β-cyclodextrin derivatives, as well as instrumental studies (NMR, FT-IR, HPLC) of preparations of real inclusion complexes. The approach adopted now can contribute to a better understanding of the phenomenon used in the development of water purification technologies.

Comparing coupled cluster and composite quantum chemical methods for computing activation energies and reaction enthalpies of radical propagation reactions

Accurate determination of activation energies and reaction enthalpies is essential for understanding the propagation step in free radical polymerization, as it significantly affects polymer chain length and structure. In this study, we compare DLPNO-CCSD(T) to canonical CCSD(T) for 17 radical addition activation energies and 18 reaction enthalpies from Radom and Fischer's test set. Additionally, we compare the computationally efficient composite methods G3(MP2)-RAD and CBS-RAD against CCSD(T)/aug-cc-pVTZ and DLPNO-CCSD(T)/CBS methods. Compared to the CCSD(T)/aug-cc-pVTZ reference, our results indicate that DLPNO-CCSD(T)/CBS with unrestricted Hartree-Fock (UHF) or UB3LYP reference orbitals and NormalPNO parameters consistently achieves chemical accuracy, with mean absolute deviations of 3.5 kJ mol-1 for activation energies and 1.5 kJ mol-1 for reaction enthalpies. Comparing the two composite methods shows that CBS-RAD agrees most closely with coupled cluster reaction enthalpies, while G3(MP2)-RAD tracks the activation energies most closely.

Sodium Alkyl(trimethylsilyl)amides: Substituent- and Solvent-dependent Solution Structures and Reactivities

The preparation of sodium isopropyl(trimethylsilyl)amide (NaPTA), sodium (1-phenylethyl)(trimethylsilyl)amide (NaPETA), sodium tert-butyl(trimethylsilyl)amide (NaBTA), and isotopologues [15N]NaPTA and [15N]NaBTA are described. Solution structural studies using a combination of 29Si NMR spectroscopy, the Method of Continuous Variations, and density functional theory computations provided insights into aggregation and solvation in a range of solvents including toluene, N,N-dimethylethylamine, triethylamine, MTBE, THF, 1,2-dimethoxyethane (DME), diglyme, N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'-tetramethylcyclohexanediamine (TMCDA), N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDTA). 12-crown-4, 15-crown-5, and 18-crown-6 revealed solvent- and substituent-dependent dimer-monomer mixtures with affiliated solvation numbers. Complexation of the three crown ethers documented both crown and substituent dependencies. Qualitative studies of reactivity showed a variety of reactions of NaPETA. Aminolysis of methyl benzoate with dialkylamines mediated by NaPTA afforded high yields of benzamides. Quantitative rate studies of aminolysis of methyl benzoate by NaPTA revealed a 47,000-fold range of rates. Detailed rate studies in toluene and THF showed dimer-based mechanisms. The role of primary- and secondary-shell solvation by THF is discussed, including nuances of methods used to separate the two contributions. PMDTA-solvated NaPTA monomer reacts as a monomer whereas bis-diglyme solvated monomer reacts as a dimer. Rate studies exploring the structure-reactivity correlations of the three crown ethers show mono- and bis-crown-based pathways in which 15-crown-5─the crown ether often said to be of choice for sodium─was decidedly inferior as an accelerant.

Spiers Memorial Lecture: Quantum chemistry, classical heuristics, and quantum advantage

We describe the problems of quantum chemistry, the intuition behind classical heuristic methods used to solve them, a conjectured form of the classical complexity of quantum chemistry problems, and the subsequent opportunities for quantum advantage. This article is written for both quantum chemists and quantum information theorists. In particular, we attempt to summarize the domain of quantum chemistry problems as well as the chemical intuition that is applied to solve them within concrete statements (such as a classical heuristic cost conjecture) in the hope that this may stimulate future analysis.

Adsorption and vibrational spectroscopy of CO on the surface of MgO from periodic local coupled-cluster theory

The adsorption of CO on the surface of MgO has long been a model problem in surface chemistry. Here, we report periodic Gaussian-based calculations for this problem using second-order perturbation theory (MP2) and coupled-cluster theory with single and double excitations (CCSD) and perturbative triple excitations [CCSD(T)], with the latter two performed using a recently developed extension of the local natural orbital approximation to problems with periodic boundary conditions. The low cost of periodic local correlation calculations allows us to calculate the full CCSD(T) binding curve of CO approaching the surface of MgO (and thus the adsorption energy) and the two-dimensional potential energy surface (PES) as a function of the distance from the surface and the CO stretching coordinate. From the PES, we obtain the fundamental vibrational frequency of CO on MgO, whose shift from the gas phase value is a common experimental probe of surface adsorption. We find that CCSD(T) correctly predicts a positive frequency shift upon adsorption of +14.7 cm-1, in excellent agreement with the experimental shift of +14.3 cm-1. We use our CCSD(T) results to assess the accuracy of MP2, CCSD, and several density functional theory (DFT) approximations, including exchange correlation functionals and dispersion corrections. We find that MP2 and CCSD yield reasonable binding energies and frequency shifts, whereas many DFT calculations overestimate the magnitude of the adsorption energy by 5-15 kJ mol-1 and predict a negative frequency shift of about -20 cm-1, which we attribute to self-interaction-induced delocalization errors that are mildly ameliorated with hybrid functionals. Our findings highlight the accuracy and computational efficiency of the periodic local correlation for the simulation of surface chemistry with accurate wavefunction methods.

Best-of-both-worlds computational approaches to difficult-to-model dissociation reactions on metal surfaces

The accurate modeling of dissociative chemisorption of molecules on metal surfaces presents an exciting scientific challenge to theorists, and is practically relevant to modeling heterogeneously catalyzed reactive processes in computational catalysis. The first important scientific challenge in the field is that accurate barriers for dissociative chemisorption are not yet available from first principles methods. For systems that are not prone to charge transfer (for which the difference between the work function of the surface and the electron affinity of the molecule is larger than 7 eV) this problem can be circumvented: chemically accurate barrier heights can be extracted with a semi-empirical version of density functional theory (DFT). However, a second important challenge is posed by systems that are prone to (full or partial) electron transfer from the surface to the molecule. For these systems the Born-Oppenheimer approximation breaks down, and currently no method of established accuracy exists for modeling the resulting effect of non-adiabatic energy dissipation on the dissociative chemisorption reaction. Because two problems exist for this class of reactions, a semi-empirical approach to computing barrier heights, which would demand that computed and experimental dissociative chemisorption probabilities match, is unlikely to work. This Perspective presents a vision on how these two problems may be solved. We suggest an approach in which parameterized density functionals are used as in the previous semi-empirical approach to DFT, but in which the parameters are based on calculations with first principles electronic structure methods. We also suggest that the diffusion Monte-Carlo (DMC) and the random phase approximation (RPA) probably are the best two first principles electronic structure methods to pursue in the framework of the approach that we call first-principles based DFT (FPB-DFT) - providing DMC and the RPA with a steppingstone towards benchmarking and future applications in computational catalysis. Probably the FPB density functional is best based on screened hybrid exchange in combination with non-local van der Waals correlation. We also propose a new electronic friction method called scattering potential friction (SPF) that could combine the advantages and avoid the disadvantages of the two main existing electronic friction approaches for describing non-adiabatic effects: by extracting an electronic scattering potential from a DFT calculation for the full molecule-metal surface system, it might be possible to compute friction coefficients from scattering phase shifts in a computationally convenient and robust fashion. Combining the FPB-DFT and SPF methods may eventually result in barrier heights of chemical accuracy for the difficult-to-model class of systems that are prone to charge transfer. This should also enable the construction of a representative database of barrier heights for dissociative chemisorption on metal surfaces. Such a database would allow testing new density functionals, or, more generally, new electronic structure approaches on a class of reactions that is of huge importance to the chemical industry. Additionally, the difficult-to-model sub-class of systems we focus on is essential to sustainable chemistry and important for a sustainable future. Adding the database envisaged to large databases already existing but mostly addressing gas phase chemistry will enable testing density functionals that have a claim to universality, i.e., to be good for all chemical systems of importance. We also make a suggestion for how to develop such a generally applicable functional, which should have the correct asymptotic dependence of the exchange contribution to the energy in both the gas phase and the metal. Finally we suggest some improvements in the representation of potential energy surfaces and in dynamics methods that would help with the validation of the proposed methods.

Exploring Thermal Stability, Vibrational Properties, and Biological Assessments of Dichloro(l-histidine)copper(II): A Combined Theoretical and Experimental Study

Dichloro(l-histidine)copper(II) crystal ([Cu(l-His)Cl2] complex) was obtained by the slow evaporation method and characterized concerning its thermal stability, phase transformations, and electronic and vibrational properties. X-ray diffraction (XRPD) confirmed that this complex crystallizes with an orthorhombic structure (P212121 space group). Thermal analyses (TG and DTA) demonstrate stability from ambient temperature up to 460 K, followed by a phase transition from the orthorhombic structure to the amorphous form around 465 K, as confirmed by temperature-dependent XRPD studies. The active modes in Fourier transform infrared (FT-IR) and Raman spectroscopy spectra were suitably assigned via density functional theory (DFT) calculations. Additionally, Hirshfeld surface analysis uncovered the prominence of Cl···H, O···H, and H···H interactions as the primary intermolecular forces within the crystal structure. The antimicrobial activity of the [Cu(l-His)Cl2] complex was investigated, demonstrating significant efficacy against Gram-positive bacteria (Staphylococcus aureus), Gram-negative bacteria (Pseudomonas aeruginosa), and fungi (Candida albicans). The minimum inhibitory concentration and cell viability tests showed that the complex inhibits the growth of S. aureus bacteria at a concentration of 1.5 μM without causing damage to the human cell line. The pharmacokinetic parameters corroborate the other tested parameters and highlight the [Cu(l-His)Cl2] complex as a promising alternative for future clinical trials and medicinal applications. The alignment of the pharmacokinetic parameters with other tested criteria highlights the potential of the [Cu(l-His)Cl2] complex as a promising candidate for future clinical studies.

A comparative study on the interaction of M3+(H2O)5-6 ions (M = Fe, Ru, and Os) with the hydroxy group

CONTEXT

The heavy metal ions are the typical carcinogenic agents. Up to now, the interaction mechanism of toxic metal ions with the biomolecules such as carbohyrate have not been elucidated and reported in the detail. In this research work, the adjacent dissociation Gibbs energy (EAB) of M3+(H2O)5(R-OH) complexes depended significantly on the molecular volume of primary alcohols and the inductive effects of substituent R in primary alcohols (R = CH3, CH3CH2, CH3CH2CH2, CH3CH2CH2CH2, Cl-CH2, F-CH2) as well as the length of linear cellulose. The affinity of M3+(H2O)5 ions with the sixth water molecule in gas phase reduced in the order as follows: Fe3+  > Ru3+  > Os3+, which were determined by the EAB values and bond lengths of M-O. The water solvent made the EAB values of Fe3+(H2O)6 ions and Fe3+(H2O)5(CH3OH) ions changed completely in the case of the polarizable continuum model, while the Onsager model gave the good agreement with the gas phase model.

METHODS

The nature of interaction between hydrated Fe3+(H2O)5 ion and the hydroxy groups of primary alcohols were investigated using density functional theory method at the B3LYP/6-311 + G** level, the PBEPBE/6-311 + G** level. The influence of water solvent was evaluated using the Onsager model and the polarizable continuum model. The two-layer ONIOM approach and the local softness analysis were employed for the hydroxy groups of linear cellulose at the B3LYP/6-311 + G**:HF/6-31G* level. The affinity of M3+(H2O)5 ions (M = Fe, Ru, and Os) with the sixth water molecule were probed at the B3LYP/QZVPP/6-311 + G** level (QZVPP basis set for the metal atoms).

Smooth Dispersion Is Physically Appropriate: Assessing and Amending the D4 Dispersion Model

The addition of dispersion corrections to density functionals is essential for accurate energy and geometry predictions. Among them, the D4 scheme is popular due to its low computational cost and high accuracy. However, due to its design, the D4 correction can occasionally lead to anomalies, such as unphysical curvature and bumps in the potential energy surface. We find these anomalies are common in the D4 model, although observable consequences are rarer than in the D3 model for reasons we explain. Nevertheless, we uncover instances of unphysical local minima and stationary points with the D4 scheme and propose two solutions that yield smoother dispersion energy as a function of nuclear position. One is trivial to implement, based on a smoother reparametrization of Gaussian weighting (D4S) to find the effective coordination number. The other replaces Gaussian weighting with soft linear interpolation (D4SL). These new approaches usually remove artificial extremum points, while maintaining accuracy.

Decomposition and Growth Pathways for Ammonium Nitrate Clusters and Nanoparticles

Understanding the formation and decomposition mechanisms of aerosolized ammonium nitrate species will lead to improvements in modeling the thermodynamics and kinetics of aerosol haze formation. Studying the sputtered mass spectra of cation and anion ammonium nitrate clusters can provide insights as to which growth and evaporation pathways are favored in the earliest stages of nucleation and thereby guide the development and use of accurate models for intermolecular forces for these systems. Simulated annealing Monte Carlo optimization followed by density functional theory optimizations can be used reliably to predict minimum-energy structures and interaction energies for the cation and anion clusters observed in mass spectra as well as for neutral nanoparticles. A combination of translational and rotational mag-walking and sawtooth simulated annealing methods was used to find optimum structures of the various heterogeneous clusters identifiable in the mass spectra. Following these optimizations with ωB97X-D3 density functional theory calculations made it possible to rationalize the pattern of peaks in the mass spectra through computation of the binding energies of clusters involved in various growth and dissociation pathways. Testing these calculations against CCSD(T) and MP2 predictions of the structures and binding energies for small clusters demonstrates the accuracy of the chosen model chemistry. For the first time, the peaks corresponding with all detectable species in both the positive and negative ion mass spectra of ammonium nitrate are identified with their corresponding structures. Thermodynamic control of particle growth and decomposition of ions due to loss of ammonia or nitric acid molecules is indicated. Structures and interaction energies for larger (NH4NO3)n nanoparticles are also presented, including the prediction of new particle morphologies with trigonal pyramidal character.

Very-Large-Scale GPU-Accelerated Nuclear Gradient of Time-Dependent Density Functional Theory with Tamm-Dancoff Approximation and Range-Separated Hybrid Functionals

Modern graphics processing units (GPUs) provide an unprecedented level of computing power. In this study, we present a high-performance, multi-GPU implementation of the analytical nuclear gradient for Kohn-Sham time-dependent density functional theory (TDDFT), employing the Tamm-Dancoff approximation (TDA) and Gaussian-type atomic orbitals as basis functions. We discuss GPU-efficient algorithms for the derivatives of electron repulsion integrals and exchange-correlation functionals within the range-separated scheme. As an illustrative example, we calculate the TDA-TDDFT gradient of the S1 state of a full-scale green fluorescent protein with explicit water solvent molecules, totaling 4353 atoms, at the ωB97X/def2-SVP level of theory. Our algorithm demonstrates favorable parallel efficiencies on a high-speed distributed system equipped with 256 Nvidia A100 GPUs, achieving >70% with up to 64 GPUs and 31% with 256 GPUs, effectively leveraging the capabilities of modern high-performance computing systems.

Role of Intermolecular Interactions in Deep Eutectic Solvents for CO2 Capture: Vibrational Spectroscopy and Quantum Chemical Studies

Recent research and reviews on CO2 capture methods, along with advancements in industry, have highlighted high costs and energy-intensive nature as the primary limitations of conventional direct air capture and storage (DACS) methods. In response to these challenges, deep eutectic solvents (DESs) have emerged as promising absorbents due to their scalability, selectivity, and lower environmental impact compared to other absorbents. However, the molecular origins of their enhanced thermal stability and selectivity for DAC applications have not been explored before. Therefore, the current study focuses on a comprehensive investigation into the molecular interactions within an alkaline DES composed of potassium hydroxide (KOH) and ethylene glycol (EG). Combining Fourier transform infrared (FT-IR) and quantum chemical calculations, the study reports structural changes and intermolecular interactions induced in EG upon addition of KOH and its implications on CO2 capture. Experimental and computational spectroscopic studies confirm the presence of noncovalent interactions (hydrogen bonds) within both EG and the KOH-EG system and point to the aggregation of ions at higher KOH concentrations. Additionally, molecular electrostatic potential (MESP) surface analysis, natural bond orbital (NBO) analysis, quantum theory of atoms-in-molecules (QTAIM) analysis, and reduced density gradient-noncovalent interaction (RDG-NCI) plot analysis elucidate changes in polarizability, charge distribution, hydrogen bond types, noncovalent interactions, and interaction strengths, respectively. Evaluation of explicit and hybrid models assesses their effectiveness in representing intermolecular interactions. This research enhances our understanding of molecular interactions in the KOH-EG system, which are essential for both the absorption and desorption of CO2. The study also aids in predicting and selecting DES components, optimizing their ratios with salts, and fine-tuning the properties of similar solvents and salts for enhanced CO2 capture efficiency.

A Critical Evaluation of the Hybrid KS DFT Functionals Based on the KS Exchange-Correlation Potentials

We have developed a critical methodology for the evaluation of the quality of hybrid exchange-correlation (XC) density functional approximations (DFAs) based on very fundamental quantities, i.e., Kohn-Sham (KS) XC potentials, self-consistent electron densities, first ionization potentials (IPs), and total energies. Since the XC potentials, the primary objects in the current study, are not directly accessible for the hybrids, we calculate them by inverting the KS electron densities. Utilizing this methodology, we tested 155 hybrid DFAs available in the LIBXC library using FCI and CCSD(T) methods as a reference. We have found that a group of functionals produces very decent XC potentials, mainly those with a large mixture of Hartree-Fock exchange. Moreover, the value of IP strongly depends on the XC potential quality. On the other hand, we show that the XC energy is dominated by functional-driven error, which in some cases leads to substantial errors in electronic densities. The study shows new directions for constructing more accurate XC functionals within the KS-DFT framework.

Accurately Predicting Barrier Heights for Radical Reactions in Solution Using Deep Graph Networks

Quantitative estimates of reaction barriers and solvent effects are essential for developing kinetic mechanisms and predicting reaction outcomes. Here, we create a new data set of 5,600 unique elementary radical reactions calculated using the M06-2X/def2-QZVP//B3LYP-D3(BJ)/def2-TZVP level of theory. A conformer search is done for each species using TPSS/def2-TZVP. Gibbs free energies of activation and of reaction for these radical reactions in 40 common solvents are obtained using COSMO-RS for solvation effects. These balanced reactions involve the elements H, C, N, O, and S, contain up to 19 heavy atoms, and have atom-mapped SMILES. All transition states are verified by an intrinsic reaction coordinate calculation. We next train a deep graph network to directly estimate the Gibbs free energy of activation and of reaction in both gas and solution phases using only the atom-mapped SMILES of the reactant and product and the SMILES of the solvent. This simple input representation avoids computationally expensive optimizations for the reactant, transition state, and product structures during inference, making our model well-suited for high-throughput predictive chemistry and quickly providing information for (retro-)synthesis planning tools. To properly measure model performance, we report results on both interpolative and extrapolative data splits and also compare to several baseline models. During training and testing, the data set is augmented by including the reverse direction of each reaction and variants with different resonance structures. After data augmentation, we have around 2 million entries to train the model, which achieves a testing set mean absolute error of 1.16 kcal mol-1 for the Gibbs free energy of activation in solution. We anticipate this model will accelerate predictions for high-throughput screening to quickly identify relevant reactions in solution, and our data set will serve as a benchmark for future studies.

Charting the coordinative landscape of the 18F-Sc/44Sc/177Lu triad with the tri-aza-cyclononane (tacn) scaffold

The widely established PET isotope 18F does not have a therapeutic partner. We have recently established that the Sc-F bond can be formed under aqueous, high yielding conditions, paving the way to providing 18F as diagnostic partners to 47Sc and 177Lu radiotherapeutics. Here, we synthesized a library of tacn-based chelators comprised of 10 structurally unique permutations incorporating acetate, methyl-benzylamide and picolinate donor arms. The chelator library encompasses chelators ranging from 6- to 9-dentate, and produces complex changes ranging from +3 to -1. The corresponding Sc-F/Sc and Lu chelate complexes were characterized using computational, spectroscopic and potentiometric methods, followed by optimization of radiolabeling with 18F, 44Sc and 177Lu and concluded by in vivo validation. We identify characterization benchmarks that chart the coordinative landscape of radiochelation approaches for this unusual triad. Our screening identifies two ligand systems, H2L111 and H3L201 as ideal, readily functionalizable constructs for prospective, targeted theranostic applications with 18F/44Sc/177Lu.

Theoretical Kinetics of Radical-Radical Reaction NH2ṄH + ṄH2 and Its Implications for Monomethylhydrazine Pyrolysis Mechanism

Significant discrepancies were observed between the experiments and the simulations for ṄH2 time-histories in monomethylhydrazine pyrolysis with the robust mechanism proposed by Pascal and Catoire. The rate of formation analyses for ṄH2 indicated the significance of the reaction NH2ṄH + ṄH2 = H2NN + NH3, which has not been well-defined. In this study, ab initio calculations were performed for the theoretical description of the NH2ṄH + ṄH2 chemistry. Most stationary points on the potential energy surface were quantified at the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ level, and the multireference methods were employed for barrier-less reaction and some transition states. The temperature- and pressure-dependent rate coefficients were determined using classical and microcanonical variational transition state theories. Four primary reaction channels were identified as competitive: 1) The H atom abstraction reaction yielding N2H2(T) + NH3, dominating at 1350-3000 K across the 0.001-100 atm pressure range. 2) The H atom abstraction reaction forming N2H2(S) + NH3, dominating at 800-1350 K and competing with the processes of chemical activation and collisional stabilization below 800 K. 3) The chemical-activated reaction resulting in H2NN(S) + NH3, dominating below 800 K at 0.001 atm. 4) The collisional-stabilized recombination reaction leading to N3H5, becoming significant as pressure increases and dominating below 600 and 650 K at 1 and 100 atm, respectively. The implications of newly calculated NH2ṄH + ṄH2 kinetics for the monomethylhydrazine pyrolysis mechanism were evaluated, and updates were implemented. Sensitivity analyses indicated the necessity of additional research efforts to comprehend the dynamics of CH3NH2 unimolecular and N2H2 + ṄH2 reaction systems. The rate coefficients presented in this study can be employed to develop the chemical kinetic model of nitryl-containing systems.

DFT and TD-DFT studies to elucidate the configurational isomers of ferric aerobactin, ferric petrobactin, and their ferric photoproducts

Iron-chelating siderophores such as aerobactin and petrobactin are produced by marine bacteria to sequester iron under low iron stress. Those that contain a citrate moiety undergo light-catalyzed ligand-to-metal charge transfer, inducing decarboxylation and formation of photoproducts. In this work, we employed density functional theory to obtain the optimized geometries and determine the relative energies and geometric parameters of different configurations of Fe(III)-coordinated aerobactin, petrobactin, and their photoproducts. Time-dependent density functional theory was then used to compute the UV-Vis absorption spectra of these species, and the comparison against experimental spectra further elucidated the structural configurations most likely to be adopted by these compounds. Frequency calculations provided Fe-O force constants on the same order as other siderophores. The relative energies and predicted spectra support the cis-cis C-fac configuration for ferric aerobactin and the cis-trans C-mer configuration for its photoproduct, while only mild support is found for specific configurations of the ferric petrobactin structures (meta-mer and meta-fac for the precursor, cis-cis para-fac for the photoproduct). The predicted ferric petrobactin spectra are found to be fairly insensitive to the configuration of the ferric complex.

Exploring non-covalent interactions in excited states: beyond aromatic excimer models

Time-dependent density functional theory (TD-DFT) offers a relatively accurate and inexpensive approach for excited state calculations. However, conventional TD-DFT may suffer from the same poor description of non-covalent interactions (NCIs) which is known from ground-state DFT. In this work we present a comprehensive benchmark study of TD-DFT for excited-state NCIs. This is achieved by calculating dissociation curves for excited complexes ('exciplexes'), whose binding strength depends on excited-state NCIs including electrostatics, Pauli repulsion, charge-transfer, and London dispersion. Reference dissociation curves are calculated with the reasonably accurate wave function method SCS-CC2/CBS(3,4) which is used to benchmark a range of TD-DFT methods. Additionally, we test the effect of ground-state dispersion corrections, DFT-D3(BJ) and VV10, for exciplex binding. Overall, we find that TD-DFT methods generally under-bind exciplexes which can be explained by the missing dispersion forces. Underbinding errors reduce going up the rungs of Jacob's ladder. Further, the D3(BJ) dispersion correction is essential for good accuracy in most cases. Likewise, the VV10-type non-local kernel yields relatively low errors and has comparable performance in either its fully self-consistent implementation or as a post-SCF additive correction, but its impact is solely on ground-state energies and not on excitation energies. From our analysis, the most robust TD-DFT methods for exciplexes with localised excitations in their equilibrium and non-equilibrium geometries are the double hybrids B2GP-PLYP-D3(BJ) and B2PLYP-D3(BJ). Their range-separated versions ωB2(GP-)PLYP-D3(BJ) or the spin-opposite scaled, range-separated double hybrid SOS-ωB88PP86 can be recommended when charge transfer plays a role in the excitations. We also identify the need for a state-specific dispersion correction as the next step for improved TD-DFT performance.

Nature of Charge Transfer Effects in Complexes of Dopamine Derivatives Adsorbed on Graphene-Type Nanostructures

Continuing the investigation started for dopamine (DA) and dopamine-o-quinone (DoQ) (see, the light absorption and charge transfer properties of the dopamine zwitterion (called dopamine-semiquinone or DsQ) adsorbed on the graphene nanoparticle surface is investigated using the ground state and linear-response time-dependent density functional theories, considering the ωB97X-D3BJ/def2-TZVPP level of theory. In terms of the strength of molecular adsorption on the surface, the DsQ form has 50% higher binding energy than that found in our previous work for the DA or DoQ cases (-20.24 kcal/mol vs. -30.41 kcal/mol). The results obtained for electronically excited states and UV-Vis absorption spectra show that the photochemical behavior of DsQ is more similar to DA than that observed for DoQ. Of the three systems analyzed, the DsQ-based complex shows the most active charge transfer (CT) phenomenon, both in terms of the number of CT-like states and the amount of charge transferred. Of the first thirty electronically excited states computed for the DsQ case, eleven are purely of the CT type, and nine are mixed CT and localized (or Frenkel) excitations. By varying the adsorption distance between the molecule and the surface vertically, the amount of charge transfer obtained for DA decreases significantly as the distance increases: for DoQ it remains stable, for DsQ there are states for which little change is observed, and for others, there is a significant change. Furthermore, the mechanistic compilation of the electron orbital diagrams of the individual components cannot describe in detail the nature of the excitations inside the complex.

Optimal balance: alkali metal-doped boron carbide nanosheets achieve superior stability and nonlinear optical responsiveness

Nonlinear optical (NLO) materials play a vital role in various technological domains, including optoelectronics and photonic devices. Designing NLO materials, particularly inorganic ones, that strike a compromise between nonlinear optical sensitivity and stability has always been a difficult task. In order to improve the stability and NLO responsiveness, we propose and examine alkali metal-doped boron carbide nanosheets (M@BCNs) in this study. Calculated interaction energies (E int), which span from -65.5 to -94.9 kcal mol-1, show the stability of the M@BCN complexes. The first hyperpolarizability value has also increased, to a maximum of 3.11 × 105 au, indicating improved nonlinear optical characteristics. QTAIM (quantum theory of atoms in molecules) and NCI (non-covalent interactions) analyses demonstrate the validity of the interactions. According to NBO (natural bond orbital) analysis, the alkali metals gain almost +1 charge. Due to the low transition energies and considerable charge transfer between the alkali metals and nanosheet, the nonlinear optical response is significantly improved. The M@BCN complexes also show transparency in the ultraviolet region, with absorption maxima ranging from 917 to 2788 nm. This study proposes a viable approach for developing alkali metal-doped boron carbide nanosheets with improved NLO response and stability.

"Hydridic Hydrogen-Bond Donors" Are Not Hydrogen-Bond Donors

Herein, we dismiss a recent proposal by Civiš, Hobza, and co-workers to modify the IUPAC definition of hydrogen bonds in order to expand the scope from protonic Y-Hδ+ to hydridic Y-Hδ- hydrogen-bond donor fragments [J. Am. Chem. Soc. 2023, 145, 8550]. Based on accurate Kohn-Sham molecular orbital (KS-MO) analyses, we falsify the conclusion that interactions involving protonic and hydridic hydrogens are both hydrogen bonds; they are not. Instead, our quantitative KS-MO, energy decomposition, and Voronoi deformation density analyses reveal two fundamentally different bonding mechanisms for protonic Y-Hδ+ and hydridic Y-Hδ- fragments which go with charge transfer in opposite directions. On one hand, we confirm the IUPAC definition for regular hydrogen bonds in the case of protonic Y-Hδ+ fragments. On the other hand, complexes involving Y-Hδ- fragments are, in fact, acceptors in other well-known families of Lewis-acid/base interactions, such as halogen bonds, chalcogen bonds, and pnictogen bonds. These mechanisms lead to the same spectroscopic phenomenon in both the Y-Hδ+ and Y-Hδ- fragments, that is, the redshift in the Y-H stretching frequency, which is, thus, not an exclusive indicator for hydrogen bonding.

The interplay of density functional selection and crystal structure for accurate NMR chemical shift predictions

Ab initio chemical shift prediction plays a central role in nuclear magnetic resonance (NMR) crystallography, and the accuracy with which chemical shifts can be predicted relative to experiment impacts the confidence with which structures can be assigned. For organic crystals, periodic density functional theory calculations with the gauge-including projector augmented wave (GIPAW) approximation and the PBE functional are widely used at present. Many previous studies have examined how using more advanced density functionals can increase the accuracy of predicted chemical shifts relative to experiment, but nearly all of those studies employed crystal structures that were optimized with generalized-gradient approximation (GGA) functionals. Here, we investigate how the accuracy of the predicted chemical shifts in organic crystals is affected by replacing GGA-level PBE-D3(BJ) crystal geometries with more accurate hybrid functional PBE0-D3(BJ) ones. Based on benchmark data sets containing 132 13C and 35 15N chemical shifts, plus case studies on testosterone, acetaminophen, and phenobarbital, we find that switching from GGA-level geometries and chemical shifts to hybrid-functional ones reduces 13C and 15N chemical shift errors by ∼40-60% versus experiment. However, most of the improvement stems from the use of the hybrid functional for the chemical shift calculations, rather than from the refined geometries. In addition, even with the improved geometries, we find that double-hybrid functionals still do not systematically increase chemical shift agreement with experiment beyond what hybrid functionals provide. In the end, these results suggest that the combination of GGA-level crystal structures and hybrid-functional chemical shifts represents a particularly cost-effective combination for NMR crystallography in organic systems.

Computational Design of Ligands for the Ir-Catalyzed C5-Borylation of Indoles through Tuning Dispersion Interactions

The indole moiety is ubiquitous in natural products and pharmaceuticals. C-H borylation of the benzenoid moiety of indoles is a challenging task, especially at the C5 position. We have combined computational and experimental studies to introduce multiple noncovalent interactions, especially dispersion, between the substrate and catalytic ligand to realize C5-borylation of indoles with high reactivity and selectivity. The successful computational predictions of new ligands should be suitable for ligand design in other transition-metal catalyzed reactions.

Structure and Intercalation of Cysteine-Asparagine-Serine Peptide into Montmorillonite as an Anti-Inflammatory Agent Preparation-A DFT Study

Peptides are receiving significant attention in pharmaceutical sciences due to their applications as anti-inflammatory drugs; however, many aspects of their interactions and mechanisms at the molecular level are not well-known. This work explores the molecular structure of two peptides-(i) cysteine (Cys)-asparagine (Asn)-serine (Ser) (CNS) as a molecule in the gas phase and solvated in water in zwitterion form, and (ii) the crystal structure of the dipeptide serine-asparagine (SN), a reliable peptide indication whose experimental cell parameters are well known. A search was performed by means of atomistic calculations based on density functional theory (DFT). These calculations matched the experimental crystal structure of SN, validating the CNS results and useful for assignments of our experimental spectroscopic IR bands. Our calculations also explore the intercalation of CNS into the interlayer space of montmorillonite (MNT). Our quantum mechanical calculations show that the conformations of these peptides change significantly during intercalation into the confined interlayer space of MNT. This intercalation is energetically favorable, indicating that this process can be a useful preparation for therapeutic anti-inflammatory applications and showing high stability and controlled release processes.

Massively Parallel Computational Chemistry with the Super Instruction Architecture and ACES4

The task of developing high-performing parallel software must be made easier and more cost-effective in order to fully exploit existing and emerging large-scale computer systems for the advancement of science. The Super Instruction Architecture (SIA) is a parallel programming platform geared toward applications that need to manage large amounts of data stored in potentially sparse multidimensional arrays during calculations. The SIA platform was originally designed for the quantum chemistry software package ACESIII. More recently, the SIA was reimplemented to overcome the limitations in the original ACESIII program. It has now been successfully employed in the new ACES4 quantum chemistry software package. This paper describes the SIA and ACES4 and illustrates their capabilities with some difficult quantum chemistry open-shell coupled-cluster benchmark calculations.

Use of Multigrids to Reduce the Cost of Performing Interpolative Separable Density Fitting

In this article, we present an interpolative separable density fitting (ISDF)-based algorithm to calculate the exact exchange in periodic mean field calculations. In the past, decomposing the two-electron integrals into the tensor hypercontraction (THC) form using ISDF was the most expensive step of the entire mean field calculation. Here, we show that by using a multigrid-ISDF algorithm, both the memory and the CPU cost of this step can be reduced. The CPU cost is brought down from cubic scaling to quadratic scaling with a low computational prefactor which reduces the cost by almost 2 orders of magnitude. Thus, in the new algorithm, the cost of performing ISDF is largely negligible compared to other steps. Along with the CPU cost, the memory cost of storing the factorized two-electron integrals is also reduced by a factor of up to 35. With the current algorithm, we can perform Hartree-Fock calculations on a diamond supercell containing more than 17,000 basis functions and more than 1500 electrons on a single node with no disk usage. For this calculation, the cost of constructing the exchange matrix is only a factor of 4 slower than the cost of diagonalizing the Fock matrix. Augmenting our approach with linear scaling algorithms can further speed up the calculations.

Naphthalimide-Based Amphiphiles: Synthesis and DFT Studies of the Aggregation and Interaction of a Simplified Model System with Water Molecules

Systems containing amphiphilic/pathic molecules have the tremendous capacity to self-assemble under appropriate conditions to form morphologies with well-defined structural order (systematic arrangement), nanometer-scale dimensions, and unique properties. In this work, the synthesis of novel naphthalimide-based amphiphilic probes that have 1,8-naphthalimide as the fluorescence signal reporting group, octyl as hydrophobic head, and PEG as hydrophilic tail, is described. These designed molecules represent a new class of self-assembling structures with some promising features. The lack of literature data on the use of 1,8-naphthalimides with cyclic and acyclic hydrophilic PEG fragments as self-assembling structures gives us the opportunity to initiate a new field in materials science. The successful synthesis of such structures is fundamental to synthetic chemistry, and computational studies of the aggregation and binding of water molecules shed light on the ability of these new systems to function as membrane water channels. This study not only expands the list of 1,8-naphthalimide derivatives but may also serve as a new platform for the development of membrane additives based on PEG-functionalized naphthalimides.

Theoretical Study of Metal-Ligand Interactions in Lead Complexes with Radiopharmaceutical Interest

The 203Pb and 212Pb lead radioisotopes are attracting growing interest as they can aid in the development of personalized, targeted radionuclide treatment for advanced and currently untreatable cancers. In the present study, the bonding interactions of Pb2+ with twelve macrocyclic ligands, having an octa and nona coordination, were assessed using Density Functional Theory (DFT) calculations. The molecular structures in an aqueous solution were computed utilizing the polarized continuum model. The preference for the twisted square antiprismatic (TSAP) structure was confirmed for ten out of the eleven cyclen-based complexes. The characteristics of the bonding were assessed using a Natural Energy Decomposition Analysis (NEDA). The analysis revealed a strong electrostatic character of the bonding in the complexes, with minor variations in electrical terms. The charge transfer (CT) had a comparable energetic contribution only in the case of neutral ligands, while in general, it showed notable variations regarding the various donor groups. Our data confirmed the general superiority of the carboxylate O and aromatic N donors. The combination of the selected efficient pendant arms pointed out the superiority of the acetate pendant arms and the lack of significant cooperation between the different pendant arms in the probed ligands. Altogether, the combination led only to a marginal enhancement in the total CTs in the complexes.

Local Second Order Mo̷ller-Plesset Theory with a Single Threshold Using Orthogonal Virtual Orbitals: A Distributed Memory Implementation

In order to alleviate the computational burden associated with superlinear compute scalings with molecular size in electron correlation methods, researchers have developed local correlation methods that wisely treat relatively small contributions as zeros but still yield accurate energy approximation. Such local correlation techniques can also be combined with parallel computing resources to obtain further efficiency and scalability. This work focuses on the distributed memory parallel implementation of a local correlation method for second order Mo̷ller-Plesset (MP2) theory. This method also only has a single threshold to control the dropping of terms and accuracy of different computing kernels in the algorithm. The process partitioning strategy and distributed parallel implementation with the message passing interface (MPI) are discussed. In particular, the algorithm relies on a fixed sparsity pattern matrix multiplication and a corresponding distributed conjugate gradient solver, which exhibits almost linear scaling in both strong and weak scaling analyses. Numerical experiments on a range of molecules, including linear chains and molecules with 2 and 3-dimensional characters, are reported. For example, with only 32 MPI ranks, this MP2 implementation can calculate the correlation energy of vancomycin in def2-TZVP basis within 0.003% accuracy (10-6.5 threshold) in half an hour, where the same problem is unfeasible to solve with sequential or pure shared memory implementations.

Is There an Adduct of Pyridine N-Oxide and Boron Trifluoride in the Gaseous State? Gas Electron Diffraction vs Mass Spectrometry

A study of saturated vapor over the pyridine N-oxide-boron trifluoride (PyO-BF3) adduct was carried out at T = 448(5) K by a synchronous gas electron diffraction/mass spectrometry (GED/MS) experiment. Due to the absence of ions in the mass spectrum, indicating the presence of a structure with an O-B dative bond, several models of vapor composition were tested by the GED method. It was found that the dominant molecular form (up to 100%) in vapor is the PyO-BF3 adduct. Using the DFT/M06-2X/aug-cc-pVTZ method, geometric optimization of the molecular ion [PyO-BF3]+ was carried out, which showed its intrinsic instability and dissociation into a [PyO]+ cation and a BF3 molecule. This study certainly demonstrates the significant advantage of the GED method to determine the qualitative and quantitative gas-phase composition of dative-bonded adducts and other noncovalent complexes as well, whereas the interpretation of mass spectra may be ambiguous due to the possible intrinsic instability of ions containing a dative bond. The nature of the O-B bond is discussed in terms of the natural bond orbitals (NBOs) and the quantum theory of atoms in molecules (QTAIM). A comparison of structural and energetic parameters for PyO-BF3 and the previously studied BF3 adducts allows the theoretical comprehension of the nature of the O-B bond to be extended and to explain the different thermal stabilities of these compounds.