Dispersion-Corrected Mean-Field Electronic Structure Methods

Antioxidant effect, DNA-binding, and transport of the flavonoid acacetin influenced by the presence of redox-active Cu(II) ion: Spectroscopic and in silico study

Acacetin (AC) is a natural polyphenol from the group of flavonoids. It is well established that the behavior of flavonoids depends on the presence of redox-active substances; therefore, we aim to investigate their biological activity following the interaction with Cu(II) ion. Our study demonstrates that AC can effectively bind Cu(II) ions, as confirmed by UV-Vis and EPR spectroscopy as well as DFT calculations. AC appears as a potent scavenger against the model ABTS radical cation by itself, but this ability is significantly limited upon Cu(II) coordination. The possible mild synergistic effect of AC in the presence of vitamin C and glutathione was also shown by the ABTS•+ test. In contrast, an inhibitory effect was observed in the presence of Cu(II) ions. The equimolar addition of AC to the model Fenton-like system containing Cu(II) did not have a noticeable effect on the concentration of hydroxyl radicals produced, but in its excess the formation of •OH decreased, as proved by EPR spin trapping. Absorption titrations and gel electrophoresis revealed effective binding to calf thymus (CT)-DNA with a stronger interaction for the Cu(II)-AC complex. The detailed mode of binding to biomolecules was described using molecular docking and molecular dynamics. Obtained results indicate that the double helix of DNA unwinds after interaction with the Cu(II)-AC complex. Fluorescence spectroscopy, employing human serum albumin (HSA), suggested a potential transport capacity for both AC and its Cu(II) complex.

Computationally efficient machine-learned model for GST phase change materials via direct and indirect learning

Phase change materials such as Ge2Sb2Te5 (GST) are ideal candidates for next-generation, non-volatile, solid-state memory due to the ability to retain binary data in the amorphous and crystal phases and rapidly transition between these phases to write/erase information. Thus, there is wide interest in using molecular modeling to study GST. Recently, a Gaussian Approximation Potential (GAP) was trained for GST to reproduce Density Functional Theory (DFT) energies and forces at a fraction of the computational cost [Zhou et al., Nat. Electron. 6, 746 (2023)]; however, simulations of large length and time scales are still challenging using this GAP model. Here, we present a machine-learned (ML) potential for GST implemented using the Atomic Cluster Expansion (ACE) framework. This ACE potential shows comparable accuracy to the GAP potential but performs orders of magnitude faster. We train the ACE potentials both directly from DFT and also using a recently introduced indirect learning approach where the potential is trained instead from an intermediate ML potential, in this case, GAP. Indirect learning allows us to consider a significantly larger training set than could be generated using DFT alone. We compare the directly and indirectly learned potentials and find that both reproduce the structure and thermodynamics predicted by the GAP and also match experimental measures of GST structure. The speed of the ACE model, particularly when using graphics processing unit acceleration, allows us to examine repeated transitions between crystal and amorphous phases in device-scale systems with only modest computational resources.

Equipartitioning of Molecular Degrees of Freedom in MD Simulations of Gaseous Systems via an Advanced Thermostatization Strategy

This work introduces a dedicated thermostatization strategy for molecular dynamics simulations of gaseous systems. The proposed thermostat is based on the stochastic canonical velocity rescaling approach by Bussi and co-workers and is capable of ensuring an equal distribution of the kinetic energy among the translational, rotational, and vibrational degrees of freedom. The outlined framework ensures the correct treatment of the kinetic energy in gaseous systems, which is typically not the case in standard approaches due to the limited number of collisions between particles associated with a large free mean path. Additionally, an efficient strategy to effectively correct for intramolecular contributions to the virial in quantum mechanical simulations is presented. The equipartitioning thermostat was successfully tested by the determination of pV diagrams for carbon dioxide and methane at the density functional tight binding level of theory. The results unequivocally demonstrate that the equipartitioning thermostat can effectively achieve an equal distribution of the kinetic energy among the different degrees of freedom, thereby ensuring correct pressure in gaseous systems. Furthermore, RDF calculations show the capability of the proposed method to accurately depict the structure of gaseous systems, as well as enable an adequate treatment of gas molecules under confinement, as exemplified by an MD simulation of (CO2)50@MOF-5.

Donor/Acceptor Ligands Based on an o-Terphenyl Motif to Achieve Thermally Activated Delayed Fluorescence in Zn(II) Complexes

The photophysical properties of six new luminescent tetrahedral Zn(II) complexes are presented that survey two electronic donor moieties (phenolate and carbazolate) and three electronic acceptors (pyridine, pyrimidine, and pyrazine). A unique ligand based on an o-terphenyl motif forms an eight-membered chelate, which enhances through-space charge-transfer (CT) interactions by limiting through-bond conjugation between the donor and acceptor. A single isomeric product was obtained in yields up to 90%. Single-crystal X-ray diffraction structures of Zn complexes incorporating either donor show complementary interligand π-π interactions. All of the Zn complexes display long-lived luminescence in the solid state consistent with emission involving the triplet state. The phenolate-based complexes show evidence of CT emission in the solid state only with the strongest (pyrazinyl) acceptor. In contrast, all carbazolate-based complexes show evidence of thermally activated delayed fluorescence (TADF) in the solid and solution state, with photoluminescent quantum yields of up to 39%. These ligands represent a new family of Zn coordination compounds demonstrating TADF/phosphorescent properties that expand upon and elucidate design principles in the pursuit of photoactive earth-abundant metal complexes.

The Noncovalent Interaction in Dinuclear Bridged Gold(I) Complexes: A Theoretical Study

We present a study of the cooperative nature of the forces dominating the interaction between gold atoms and aryl-aryl stacking. For this purpose, we modeled a series of complexes of the type dpm(AuR)2 (dpm= bis(phoshino)methane; R = -C6H5, -C6F5, -C6Cl5, and -Cl). The models were calculated at the MP2, CCSD(T), and DFT-D3(BJ) (PBE and TPSS) levels of theory. The results show Au-Au and aryl-aryl stacking distances associated with noncovalent interactions. Also, the Wiberg indices, NBO, NCI, and QTAIM analyses exposed a low-density character between the gold atoms and aryl-aryl stacking, revealing that this contribution explains the stability of the complexes via dispersive interactions. Finally, the absorption spectra obtained are comparable with the experimental ones, and the orbitals obtained demonstrate that after the transitions, the orbitals are delocalized between the gold atoms and the vertex atoms of the molecules.

Spatial Signatures of Electron Correlation in Least-Squares Tensor Hypercontraction

Least-squares tensor hypercontraction (LS-THC) has received some attention in recent years as an approach to reduce the significant computational costs of wave function-based methods in quantum chemistry. However, previous work has demonstrated that LS-THC factorization performs disproportionately worse in the description of wave function components (e.g., cluster amplitudes T̂2) than Hamiltonian components (e.g., electron repulsion integrals (pq|rs)). This work develops novel theoretical methods to study the source of these errors in the context of the real-space T̂2 kernel, and reports, for the first time, the existence of a "correlation feature" in the errors of the LS-THC representation of the "exchange-like" correlation energy EX and T̂2 that is remarkably consistent across ten molecular species, three correlated wave functions, and four basis sets. This correlation feature portends the existence of a "pair point kernel" missing in the usual LS-THC representation of the wave function, which critically depends upon pairs of grid points situated close to atoms and with interpair distances between one and two Bohr radii. These findings point the way for future LS-THC developments to address these shortcomings.

Shape-responsive host-guest chemistry: metal-free tetracationic porphyrin nonplanarity promoted by clay mineral interactions assessed by theoretical simulations

Distortions in the porphyrin core from planarity can trigger a unique structure-property relationship, imparting its basicity, chemical stability, redox potential, and excited-state energetics, among other properties. The colour change promoted by such distortion is signed by red shifts in its electronic absorption spectra. The adsorption of guest meso-substituted free-base porphyrin species onto inorganic hosts, such as clay minerals (layered aluminium or magnesium silicates), is known to further promote colour changes. However, the origin of these changes remains a subject of debate without a clear consensus. In this work, an extensive theoretical study was conducted using density functional theory (DFT) to model the interactions between tetracationic porphyrins, specifically meso-substituted groups N-methyl-4-pyridyl (p-TMPyP) and N-methyl-3-pyridyl (m-TMPyP), and montmorillonite (MMT) with the ideal formula [(Al1.67Mg0.33)Si4O10(OH)2]-0.33. The following conditions were evaluated: (i) adsorption or intercalation of p-TMPyP into MMT host structure, (ii) intercalation of m-TMPyP into MMT, and (iii) the influence of water on the intercalation process. The electrostatic interactions between the porphyrins and the MMT siloxane surface induced conformational changes in p-TMPyP, characterized by rotation of the substituent groups at the macrocycle periphery and a twist of the porphyrin plane. The nonplanarity of the intercalated p-TMPyP guest produced robust Brønsted basic sites capable of abstracting H+ ions from intercalated water molecules, resulting in the formation of a dication. The macrocycle distortion was found to decrease π-conjugation, thereby enhancing the localisation of the lone pair on the imine nitrogen atom. On the other hand, m-TMPyP exhibited slight core macrocycle deformations and minor changes in the dihedral angles of its meso-substituent groups compared to its isomer, with no observed protonation reaction upon intercalation. These findings highlight the clay microenvironment as a promising strategy for inducing conformational alterations in porphyrins, promoting nonplanarity, and exemplifying a shape-responsive system within the framework of guest-host chemistry.

Hydride and halide abstraction reactions behind the enhanced basicity of Be and Mg clusters with nitrogen bases

In this study, we investigate the protonation effects on the structure, relative stability and basicity of complexes formed by the interaction of monomers and dimers of BeX2 and MgX2 (X = H, F) with NH3, CH2NH, HCN, and NC5H5 bases. Calculations were performed using the M06-2X/aug-cc-pVTZ formalism, along with QTAIM, ELF and NCI methods for electron density analysis and MBIE and LMO-EDA energy decomposition analyses for interaction enthalpies. The protonation of the MH2- and M2H4-Base complexes occurs at the negatively charged hydrogen atoms of the MH2 and M2H4 moieties through typical hydride abstraction reactions, while protonation at the N atom of the base is systematically less exothermic. The preference for the hydride transfer mechanism is directly associated with the significant exothermicity of H2 formation through the interaction between H- and H+, and the high hydride donor ability of these complexes. The basicity of both, MH2 and M2H4 compounds increases enormously upon association with the corresponding bases, with the increase exceeding 40 orders of magnitude in terms of ionization constants. Due to the smaller exothermicity of HF formation, the basicity of fluorides is lower than that of hydrides. In Be complexes, the protonation at the N atom of the base dominates over the fluoride abstraction mechanism. However, for the Mg complexes the fluoride abstraction mechanism is energetically the most favorable process, reflecting the greater facility of Mg complexes to lose F-.

Assessment of electron-proton correlation functionals for vibrational spectra of shared-proton systems by constrained nuclear-electronic orbital density functional theory

Proton transfer plays a crucial role in various chemical and biological processes. A major theoretical challenge in simulating proton transfer arises from the quantum nature of the proton. The constrained nuclear-electronic orbital (CNEO) framework was recently developed to efficiently and accurately account for nuclear quantum effects, particularly quantum nuclear delocalization effects, in quantum chemistry calculations and molecular dynamics simulations. In this paper, we systematically investigate challenging proton transfer modes in a series of shared-proton systems using CNEO density functional theory (CNEO-DFT), focusing on evaluating existing electron-proton correlation functionals. Our results show that CNEO-DFT accurately describes proton transfer vibrational modes and significantly outperforms conventional DFT. The inclusion of the epc17-2 electron-proton correlation functional in CNEO-DFT produces similar performance to that without electron-proton correlations, while the epc17-1 functional yields less accurate results, comparable with conventional DFT. These findings hold true for both asymmetrical and symmetrical shared-proton systems. Therefore, until a more accurate electron-proton correlation functional is developed, we currently recommend performing vibrational spectrum calculations using CNEO-DFT without electron-proton correlation functionals.

Computational Modeling of Reticular Materials: The Past, the Present, and the Future

Reticular materials rely on a unique building concept where inorganic and organic building units are stitched together giving access to an almost limitless number of structured ordered porous materials. Given the versatility of chemical elements, underlying nets, and topologies, reticular materials provide a unique platform to design materials for timely technological applications. Reticular materials have now found their way in important societal applications, like carbon capture to address climate change, water harvesting to extract atmospheric moisture in arid environments, and clean energy applications. Combining predictions from computational materials chemistry with advanced experimental characterization and synthesis procedures unlocks a design strategy to synthesize new materials with the desired properties and functions. Within this review, the current status of modeling reticular materials is addressed and supplemented with topical examples highlighting the necessity of advanced molecular modeling to design materials for technological applications. This review is structured as a templated molecular modeling study starting from the molecular structure of a realistic material towards the prediction of properties and functions of the materials. At the end, the authors provide their perspective on the past, present of future in modeling reticular materials and formulate open challenges to inspire future model and method developments.

The Competition Between Cation-Anion and Cation-Triglyme Interaction in Solvate Ionic Liquids Probed by Far Infrared Spectroscopy and Molecular Dynamics Simulations

Glyme-based electrolyte solutions provide new concepts for developing suitable lithium-ion batteries. The so-called solvate ionic liquids (SILs) are promising electrolytes. They are most efficient in equimolar mixtures of lithium bis(trifluoromethanesulfonyl)imide ([Li][NTf2]) and glyme, wherein the [Li]+ cation is supposedly fully solvated by glyme molecules. Here, we performed far (FIR) and mid (MIR) infrared spectroscopy for probing the solvation and local structures around the [Li]+ ions. In particular, we studied the competition between the triglyme molecule (G3) and the salt anions for the coordination to the lithium cations with increasing [Li][NTf2] concentration. The formation of nano structures in the [Li][NTf2]:G3 mixtures is discussed in terms of contact (CIP) and solvent-separated (SIP) ion pairs in solution. At low salt concentrations, the [Li]+ cations are solvated by two triglyme molecules resulting in SIPs only. With increasing salt concentration, [Li]+ is predominantly solvated by one triglyme molecule as [Li(triglyme)1]+ but still remains in contact to one of the four oxygen atoms of the [NTf2]- anion. Molecular dynamics (MD) simulations provide a molecular picture of the [Li][NTf2]:G3 mixtures that supports the conclusions drawn from the experimental findings.

An efficient and flexible approach for local distortion: distortion distribution analysis enabled by fragmentation

Distortion can play crucial roles in influencing structures and properties, as well as enhancing reactivity or selectivity in many chemical and biological systems. The distortion/interaction or activation-strain model is a popular and powerful method for deciphering the origins of activation energies, in which distortion and interaction energies dictate an activation energy. However, decomposition of local distortion energy at the atomic scale remains less clear and straightforward. Knowing such information should deepen our understanding of reaction processes and improve reaction design. Herein, an efficient, general and flexible fragmentation-based approach was proposed to evaluate local distortion energies for various chemical and biological molecules, which can be obtained computationally and/or experimentally. Moreover, our distortion analysis is readily applicable to multiple structures from molecular dynamics (or the minimum energy path) as well as can be evaluated by different computational chemistry methods. Our systematic analysis shows that our approach not only aids computational and experimental chemists in visualizing (relative) distortion distributions within molecules (distortion map) and identifies the key distorted pieces, but also offers deeper understanding and insights into structures, reaction mechanisms and dynamics in various chemical and biological systems. Furthermore, our analysis offers indices of local distortion energy, which can potentially serve as a new descriptor for multi-linear regression (MLR) or machine learning (ML) modelling.

The V30 benchmark set for anharmonic vibrational frequencies of molecular dimers

Intermolecular vibrations are extremely challenging to describe but are the most crucial part for determining entropy and hence free energies and enable, for instance, the distinction between different crystal-packing arrangements of the same molecule via THz spectroscopy. Herein, we introduce a benchmark dataset-V30-containing 30 small molecular dimers with intermolecular interactions ranging from exclusively van der Waals dispersion to systems with hydrogen bonds. All the calculations are performed with the gold standard of quantum chemistry CCSD(T). We discuss vibrational frequencies obtained via different models starting with the harmonic approximation over independent Morse oscillators up to second-order vibrational perturbation theory (VPT2), which allows a proper anharmonic treatment including coupling of vibrational modes. However, large amplitude motions present in many low-frequency intermolecular modes are problematic for VPT2. In analogy to the often used treatment for internal rotations, we replace such problematic modes by a simple one-dimensional hindered rotor model. We compare selected dimers to the available experimental data or high-level calculations of potential energy surfaces and show that VPT2 in combination with hindered rotors can yield a very good description of fundamental frequencies for the discussed subset of dimers involving small and semi-rigid molecules.

Synthesis, XRD and DFT studies on Pb[ChCN]2 (Ch = O, S, Se) and Pb[SeCN][OH]

We report on the synthesis of Pb[ChCN]2 (Ch = O, S, Se) and Pb[SeCN][OH] and their hitherto unknown crystal structures. All products were fully characterized by single-crystal and powder X-ray diffraction. Bulk analysis was performed by Rietveld refinement, elemental analysis, differential scanning calorimetry-thermogravimetric analysis (DSC-TGA), and solid-state Raman spectroscopy. Quantum-mechanical calculations based on the density functional theory allowed optimization of the structural parameters of these lead-based compounds, as well as assessment of their electronic structures and detailed assignment and interpretation of the vibrational spectra. In addition, the origin of bands related to difficulties in assigning the exact position of H atoms in the structures was resolved.

Steric Selection of Anion Binding Sites by Organoantimony(V) Pnictogen Bond Donors: An Experimental and Computational Study

Catecholatostiboranes have emerged as useful Lewis acids in several applications. To better understand the factors that control the properties of these species, we examined the Lewis acidities of (o-C6Cl4O2)Sb(o-Tol)3 (2, Tol = tolyl) and (o-C6Cl4O2)Sb(p-Tol)3 (3), two triarylcatecholatostiboranes that differ by the nature of the aryl substituent. Fluoride anion binding studies indicate that 3 is more Lewis acidic than 2, a factor readily assigned to the steric crowding around antimony in the case of the o-tolyl derivative. But, while 3 binds F- trans to a Sb-Caryl bond as is typical of catecholatostiboranes, 2 prefers binding trans to a Sb-O bond. Computational analyses of 2 and 3 reveal the existence of several σ holes, and an activation strain analysis is employed to elucidate the origin of these stiboranes' anion-binding geometry preferences.

Pyrolytic conversion of glucose into hydroxymethylfurfural and furfural: Benchmark quantum-chemical calculations

Quantum chemical methods have been intensively applied to study the pyrolytic conversion of glucose into hydroxymethylfurfural (HMF) and furfural (FF). Herein, we collect the most relevant mechanistic proposals from the recent literature and organize them into a single reaction network. All the transition structures (TSs) and intermediates are characterized using highly accurate ab initio methods and the possible reaction pathways are assessed in terms of the Gibbs energies of the TSs and intermediates with respect to β-glucopyranose, selecting a 2D ideal-gas standard state at 773 K to represent the pyrolysis conditions. Several pathways can lead to the formation of both HMF and FF passing through rate-determining TSs that have ΔG‡ values of ~49-50 kcal/mol. Both water-assisted mechanisms and nonspecific environmental effects have a minor impact on the Gibbs energy profiles. We find that the HMF → FF + CH2O fragmentation has a small ΔrxnG value and an accessible ΔG‡ barrier. Our computational results, which are in consonance with the kinetic parameters derived from lumped models, the results of isotopic labeling experiments and the reported HMF/FF molecular ratios, could be useful for modeling studies including on nonequilibrium kinetic effects that may render more information about product yields and the relevance of the various pathways.

ConfRank: Improving GFN-FF Conformer Ranking with Pairwise Training

Conformer ranking is a crucial task for drug discovery, with methods for generating conformers often based on molecular (meta)dynamics or sophisticated sampling techniques. These methods are constrained by the underlying force computation regarding runtime and energy ranking accuracy, limiting their effectiveness for large-scale screening applications. To address these ranking limitations, we introduce ConfRank, a machine learning-based approach that enhances conformer ranking using pairwise training. We demonstrate its performance using GFN-FF-generated conformer ensembles, leveraging the DimeNet++ architecture trained on pairs of 159 760 uncharged organic compounds from the GEOM data set with r2SCAN-3c reference level. Instead of predicting only on single molecules, this approach captures relative energy differences between conformers, leading to a significant improvement of the overall conformational ranking, outperforming GFN-FF and GFN2-xTB. Thereby, the pairwise RMSD of the relative energy difference of two conformers can be reduced from 5.65 to 0.71 kcal mol-1 on the test data set, allowing to correctly identify up to 81% of all lowest lying conformers correctly (GFN-FF: 10%, GFN2-xTB: 47%). The ConfRank approach is cost-effective, allowing for scalable deployment on both CPU and GPU, achieving runtime accelerations by up to 2 orders of magnitude compared to GFN2-xTB. Out-of-sample investigations on CREST-generated conformer ensembles from the QM9 data set and conformers taken from an extended GMTKN55 data set show promising results for the robustness of this approach. Thereby, ranking correlation coefficient such as Spearman can be improved to 0.90 (GFN-FF: 0.39, GFN2-xTB: 0.84) reducing the probability of an incorrect sign flip in pairwise energy comparison from 32 to 7%. On the extended GMTKN55 subsets the pairwise MAD (RMSD) could be reduced on almost all subsets by up to 62% (58%) with an average improvement of 30% (29%). Moreover, an exemplary case study on vancomycin shows similar performance, indicating applicability to larger (bio)molecular structures. Furthermore, we motivate the usage of the pairwise training approach from a theoretical perspective, highlighting that while pairwise training can lead to a decline in single sample prediction of absolute energies for ML models, it significantly enhances conformer ranking performance. The data and models used in this study are available at https://github.com/grimme-lab/confrank.

Computational Insights into Tunable Reversible Network Materials: Accelerated ReaxFF Kinetics of Furan-Maleimide Diels-Alder Reactions for Self-Healing and Recyclability

In this study, ReaxFF molecular dynamics simulations were benchmarked and used to study the relative kinetics of the retro Diels-Alder reaction between furan and N-methylmaleimide. This reaction is very important for the creation of polymer networks with self-healing and recyclable properties, since they can be used as reversible linkers in the network. So far, the reversible Diels-Alder reaction has not yet been studied by using reactive molecular dynamics simulations. This work is, thus, the first step in simulating a covalent adaptable network (CAN) using Diels-Alder reactions as reversible linkers. For both endo and exo, the bond breaking in 40 product molecules was simulated using the bond boost method and the endo/exo ratio was evaluated. This ratio was benchmarked against density functional theory (DFT) and experimental results for a changing set of bond boost parameters. Given their importance to understand how the CAN performs, the effect of the addition of a polymer backbone and the effect of temperature were successfully simulated using our newly parametrized reactive force field.

Synthesis of Antimicrobial Norlabdane Compounds with Rearranged Cycle B and Molecular Docking Studies

The synthesis of tetra- and pentanorlabdane compounds with rearranged cycle B based on commercially available (+)-sclareolide is reported. Desired compounds were prepared from intermediate ketones via Baeyer-Villiger oxidation. The structures of synthesized compounds were confirmed by spectral IR, 1D (1H, 13C, and DEPT), and 2D (H-COSY, H,C-HSQC, H,C-HMBC, H,N-HMBC, NOESY) NMR analyses, mass-spectrometry and single crystal X-rays diffraction. Two out of the four synthesized compounds showed high antifungal and antibacterial activities comparable to and exceeding standard antifungal (caspofungin) and antibacterial (kanamycin) agents. DFT calculations show that in gas and DCM, compound 4 is more stable than 3 with a difference in the Gibbs free energy of 23.3 kJ/mol and 20.7 kJ/mol, respectively. In water and methanol, compound 3 is slightly more stable, by 2.4 kJ/mol and 2.78 kJ/mol, respectively. Molecular docking to four targets DNA gyrase from E. coli (1KZN), Fabz from P. aeruginosa (1U1Z), dihydrofolate reductase from C. albicans (3QLS) and MurB from E. coli (2Q85) showed good agreement with the results of in vitro evaluation and confirmed the biological activity of compounds 3 and 4, with binding affinities comparable and for some targets exceeding that of Caspofungin and Kanamycin.

Advancing Non-Atom-Centered Basis Methods for More Accurate Interaction Energies: Benchmarks and Large-Scale Applications

Recent advances in local electron correlation approaches have enabled the relatively routine access to CCSD(T) [that is, coupled cluster (CC) with single, double, and perturbative triple excitations] computations for molecules of a hundred or more atoms. Here, approaching their complete basis set (CBS) limit becomes more challenging due to extensive basis set superposition errors, often necessitating the use of large atomic orbital (AO) basis sets with diffuse functions. Here, we study a potential remedy in the form of non-atom-centered or floating orbitals (FOs). FOs are still rarely employed even for small molecules due to the practical complication of defining their position, number, exponents, etc. The most frequently used FO method thus simply places a single FO center with a large number of FOs toward the middle of noncovalent dimers; however, a single FO center for larger complexes can soon become insufficient. A recent alternative uses a grid of FO centers around the monomers with a single s function per center, which is currently applicable only for H, C, N, and O atoms. Here, we build on the above advantages and mitigate some drawbacks of previous FO approaches by using a layer of FO centers and 4-9 FOs/center for each monomer. Thus, a double layer of FOs is placed between the interacting subsystems. When extending the double-ζ AO basis with this double layer of FOs, the quality of conventional augmented double-ζ or conventional triple-ζ AO bases can be reached or surpassed with less orbitals, leading to few tenths of a kcal/mol basis set errors for medium-sized dimers. This good performance extends to larger molecules (shown here up to 72 atoms), as efficient local natural orbital (LNO) CCSD(T) computations with only double-ζ AO and 4 FOs/center FO bases match our LNO-CCSD(T)/CBS reference within ca. 0.1 kcal/mol. These developments introduce FO methods to the accurate modeling of large molecular complexes without limitations to atom types by further accelerating efficient correlation calculations, like LNO-CCSD(T).

How to Assess and Predict Electrical Double Layer Properties. Implications for Electrocatalysis

The electrical double layer (EDL) plays a central role in electrochemical energy systems, impacting charge transfer mechanisms and reaction rates. The fundamental importance of the EDL in interfacial electrochemistry has motivated researchers to develop theoretical and experimental approaches to assess EDL properties. In this contribution, we review recent progress in evaluating EDL characteristics such as the double-layer capacitance, highlighting some discrepancies between theory and experiment and discussing strategies for their reconciliation. We further discuss the merits and challenges of various experimental techniques and theoretical approaches having important implications for aqueous electrocatalysis. A strong emphasis is placed on the substantial impact of the electrode composition and structure and the electrolyte chemistry on the double-layer properties. In addition, we review the effects of temperature and pressure and compare solid-liquid interfaces to solid-solid interfaces.

Iron Impurity Impairs the CO2 Capture Performance of MgO: Insights from Microscopy and Machine Learning Molecular Dynamics

Magnesium oxide (MgO) is a promising sorbent for direct air capture (DAC) of carbon dioxide. Iron (Fe) is a common impurity in naturally occurring MgO and minerals used to produce MgO, yet a molecular-scale understanding of Fe-doping effects on carbonation is lacking. Here, we observed reduced carbonation performance in Fe-doped MgO experimentally. The energetics of adsorbing a (bi)carbonate ion on pristine and Fe-doped MgO(001) surfaces were further investigated using ab initio and machine learning potential molecular dynamics coupled with metadynamics simulations. Both pristine and Fe-doped surfaces exhibited a basic (OH-) hydration layer, where the (bi)carbonate ion adsorption is thermodynamically favorable. However, the dissolution of surface Fe had smaller energy barriers and was more favorable than Mg. Leached Fe likely neutralized the near-surface basicity, yielding reduced reactivity on Fe-doped MgO. Our observations offer critical insights for material selection and emphasize the importance of evaluating the geologic origin of earth materials used for DAC.

MoSe2-Layered Nanosheet Decorated SnO2 Hollow Nanofiber-Based Highly Sensitive and Selective Room Temperature H2S Gas Sensor

In this work, we successfully demonstrated a MoSe2@SnO2 nanocomposite-based room temperature H2S gas sensor. A sensing mechanism was proposed based on experimental results and density functional theory calculations. The FESEM micrographs of the heterostructure formed by hydrothermally grown MoSe2-layered nanosheets and SnO2-hollow nanofiber result in a high surface area for H2S gas adsorption. On exposure to calcination, the electro-spun PVP/SnO2 nanofiber undergoes the Kirkendall phenomenon, resulting in 94.6 nm thick hollow nanofibers. The combination of TMD@SMO shows an abundance of charge transfer, resulting in an excellent response toward H2S gas. The MoSe2@SnO2 detects a low concentration of 500 ppb with a relative response of ∼19.9% at room temperature (RT). The simulation, using density functional theory (DFT), discloses that the adsorption energies ranged from -0.3645 to -0.5193 eV, indicating reduced bond lengths and significant H2S interactions. The sensor proves an excellent sensitivity toward H2S gas, ranging from 100 ppm to 500 ppb, with a LoD of ∼15 ppb at RT. As the sensor worked at RT with accuracy and reliability, consistent performance was observed upon exposure to various humidity levels, making it suitable for exhaled breath gas sensors. The sensor, as developed, also exhibited a good selectivity toward H2S gas in contrast to other gases as well as stability and longevity over time.

Tailoring superstructure units for improved oxygen redox activity in Li-rich layered oxide battery's positive electrodes

The high-voltage oxygen redox activity of Li-rich layered oxides enables additional capacity beyond conventional transition metal (TM) redox contributions and drives the development of positive electrode active materials in secondary Li-based batteries. However, Li-rich layered oxides often face voltage decay during battery operation. In particular, although Li-rich positive electrode active materials with a high nickel content demonstrate improved voltage stability, they suffer from poor discharge capacity. Here, via physicochemical and electrochemical measurements, we investigate the correlation between oxygen redox activity and superstructure units in Li-rich layered oxides, specifically the fractions of LiMn6 and Ni4+-stabilized LiNiMn5 within the TM layer. We prove that an excess of LiNiMn5 hinders the extraction/insertion of lithium ions during Li metal coin cell charging/discharging, resulting in incomplete oxygen redox activity at a cell potential of about 3.3 V. We also demonstrate that lithium content adjustment could be a beneficial approach to tailor the superstructure units. Indeed, we report an improved oxygen redox reversibility for an optimized Li-rich layered oxide with fewer LiNiMn5 units.

Cation-lone Pair Interaction in Alkali/Alkaline Earth Metal Ion-Heavier Borazine Analogue Complexes

The present study is the first report on the formation of alkali/alkaline earth metal ion-heavier borazine analogue complexes via cation-lone pair interaction. Density functional calculations are performed in scrutinizing the complex formation between alkali (Li+, Na+, K+)/alkaline earth (Be2+, Mg2+, Ca2+) metal ions and heavier borazine analogues (HBA) viz. B3P3H6, Al3N3H6, Al3P3H6, Al3As3H6, and Ga3P3H6. The complexes are found to be stable in gas phase with stabilization energies within the range 26.40-324.74 kcal mol-1. The stability can be attributed to the polarizing power of the involved metal ions. Presence of solvent phase exerted notable impact on the stability of the complexes; stability is reduced significantly with the increase in solvent polarity. The process of complexation is exothermic and spontaneous. QTAIM analysis indicated the presence of both ionic and covalent interaction between HBAs and metal ions. HOMO energy, Wiberg bond index, NCI-isosurface and RDG plot analysis revealed the major role of cation-lone pair interaction in the complexation process.

Light-Controlled Anticancer Activity and Cellular Uptake of a Photoswitchable Cisplatin Analogue

A photoactive analogue of cisplatin was synthesized with two arylazopyrazole ligands, able to undergo trans-cis/cis-trans photoisomerizations. The cis photoisomer showed a dark half-life of 9 days. The cytotoxicities of both photoisomers of the complex were determined in several cancer and normal cell lines and compared to that of cisplatin. The trans photoisomer of the complex was much more cytotoxic than both the cis photoisomer and cisplatin, and was more toxic for cancer (4T1) than for normal (NMuMG) murine breast cells. 4T1 cell death occurred through necrosis. Photoisomerization of the trans and cis photoisomers internalized by the 4T1 cells increased and decreased their viability, respectively. The cellular uptake of the trans photoisomer was stronger than that of both the cis photoisomer and cisplatin. Both photoisomers interacted with DNA faster than cisplatin. The trans photoisomer was bound stronger by bovine serum albumin and induced a greater decrease in cellular glutathione levels than the cis photoisomer.

A Gravitational-like Relationship of Dispersion Interactions is Exhibited by 40 Pairs of Molecules and Noble Gas Atoms

We present computational results of many-body dispersion (MBD) interactions for 40 pairs of molecular and atomic species: hydrocarbons, silanes, corresponding fluorinated derivatives, pairs which have multiple H---H contacts between the molecules, as well as pairs having π-π interactions, and pairs of noble gases. The calculations reveal that the MBD stabilization energy (EDISP,MBD) obeys a global relationship, which is gravitational-like. It is proportional to the product of the masses of the two molecules (M1M2) and inversely proportional to the corresponding distances between the molecular centers-of-mass (RCOM-COM) or the H---H distances of the atoms mediating the interactions of the two molecules (RH-H). This relationship reflects the interactions of instantaneous dipoles, which are formed by the ensemble of bonds/atoms in the interacting molecules. Using the D4-corrected dispersion energy (EDISP,D4), which accounts for three-body interactions, we find that the EDISP,MBD and EDISP,D4 data sets are strongly correlated. Based on valence-bond modeling, the dispersion interactions occur primarily due to the increased contributions of the oscillating-ionic VB structures which maintain favorable electrostatic interactions; the [Sub─C+:H-+H:C-─Sub] and [Sub─C:-+H -H:C+─Sub] structures; Sub symbolizes general residues. This augmented contribution is complemented by simultaneously diminished-weights of the destabilizing pair of structures, [Sub─C+:H--H:C+─Sub] and [Sub─:C- H++H:C-─Sub]. The local charges are propagated to the entire ensemble of bonds/atoms by partially charging the Sub residues, thus bringing about the "gravitational-like" dependence of dispersion.

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.

Ab Initio Molecular Dynamics Investigation of Water and Butanone Adsorption on UiO-66 with Defects

Volatile organic compounds (VOCs) are harmful chemicals that are found in minute quantities in the atmosphere and are emitted from a variety of industrial and biological processes. They can be harmful to breathe or serve as biomarkers for disease detection. Therefore, capture and detection of VOCs is important. Here, we have examined if the Zr-based UiO-66 metal-organic framework (MOF) can be used to capture butanone─a well-known VOC. Toward that end, we have performed Born-Oppenheimer ab initio molecular dynamics (AIMD) at 300 and 500 K to probe the energetics and molecular interactions between butanone [CH3C(O)CH2CH3] and open-cage Zr-UiO-66. Such interactions were systematically interrogated using three MOF structures: defective MOF with a missing 1,4-benzene-dicarboxylate linker and two H2O; pristine MOF with two H2O; and pristine dry MOF. These structures were loaded with one and four molecules of butanone to examine the effect of concentration as well. One-molecule loading interacted favorably with the defective structure at 300 K, only. In comparison, interactions with four-molecule loading were energetically favorable for all conditions. Persistent hydrogen bonds between the O atom of butanone, H2O, and μ3-OH hydroxyl attachments at Zr nodes substantially contributed to the intermolecular interactions. At higher loadings, butanone also showed a pronounced tendency to diffuse into the adjoining cages of Zr-UiO-66. The effect of such movement on interaction energies was rationalized using simple statistical mechanics-based models of interacting and noninteracting gases. Broadly, we learn that the presence of prior moisture within the interstitial cages of Zr-UiO-66 significantly impacts the adsorption behavior of butanone.

Robust Computation and Analysis of Vibrational Spectra of Layered Framework Materials Including Host-Guest Interactions

Layered framework materials, a rapidly advancing class of porous materials, are composed of molecular components stitched together via covalent bonds and are usually synthesized through wet-chemical methods. Computational infrared (IR) and Raman spectra are among the most important characterization tools for this material class. Besides the a priori known spectra of the molecular building blocks and the solvent, they allow for in situ monitoring of the framework formation during synthesis. Therefore, they need to capture the additional peaks from host-guest interactions and the bands from emerging bonds between the molecular building blocks, verifying the successful synthesis of the desired material. In this work, we propose a robust computational framework based on ab initio molecular dynamics (AIMD), where we compute IR and Raman spectra from the time-correlation functions of dipole moments and polarizability tensors, respectively. As a case study, we apply our methodology to a covalent organic framework (COF) material, COF-1, and present its AIMD-computed IR and Raman spectra with and without 1,4-dioxane solvent molecules in its pores. To determine robust settings, we meticulously validate our model and explore how stacking disorder and different methods for computing dipole moments and polarizabilities affect IR and Raman intensities. Using our robust computational protocol, we achieve excellent agreement with experimental data. Furthermore, we illustrate how the computed spectra can be dissected into individual contributions from the solvent molecules, the molecular building blocks of COF-1, and the bonds connecting them.

Luminescence Thermochromism of a Noncluster Copper Iodide Complex

Hybrid copper(I) halide materials are currently attracting significant attention due to their exceptional luminescence properties, offering great potential for the development of multifunctional emissive materials with, in addition, eco-friendly features. A binuclear copper iodide complex, based on the [Cu2I2L4] motif with phosphite derivatives as ligands, has been synthesized and structurally characterized. Photophysical investigations indicate that this complex displays luminescence thermochromic properties, which are characterized by a temperature-dependent change in the relative intensity of two emission bands. The high-contrast luminescence thermochromism, with an important color variation from purple to cyan, is ascribed to the thermal equilibrium of two different excited states. While thermochromism is relatively known for multimetallic complexes, the perfectly controlled thermochromism of the studied compound is unprecedented for a binuclear complex. From theoretical investigations, this original feature is due to the coordination of phosphite ligands, which induces a specific energy layout of the complex, presenting vacant orbitals of varying nature. This single-component, dual-emissive binuclear complex, displaying relevant sensitivity temperature response, presents great potential for luminescence ratiometric thermometry applications. This study underlines the relevance of the ligand engineering strategy in developing original, emissive, and sustainable copper-based materials.

Mechanism for Site-Selective Hydroboration of C70 Fullerene with Borane by DFT-D3 Study

We studied the hydroboration of the C70 fullerene using both B3LYP-D3(BJ)/6-311G(d,p) and M06-2X-D3/6-311G(d,p) levels of theory, incorporating the empirical dispersion interaction, and Fukui index calculations. Potential energy surfaces (PESs) and Gibbs free energy surfaces (GFESs) were calculated for the pathways from four BH3 adducts (located at the AB, CC, D, and E sites) on the C70 to eight products formed by the 1,2-addition of BH3 across the four [6,6]-ring fused bonds (AB, CC, DE, and EE) and across the two [5,6]-ring fused bonds (AA and DD). These pathways are two-step consecutive reactions. We denoted the positions on the fullerene cage as A through E, from the pole to the equator, based on the D5h symmetry of the C70 fullerene. In the first step reaction, the product ratios for the four adduct intermediates should be as the primary intermediate BH3(D), the secondary intermediate BH3(AB), the tertiary intermediate BH3(CC), and the minor intermediate BH3(E), based on the Fukui indices. In addition, in the second step reaction, transition states (TSs) from four adduct intermediates to eight product isomers, namely, BH2(A)H (B) to BH2(E)H (E), were obtained using the QST2 method. The calculated reaction coordinates showed exothermic reactions for all bonds except the EE bond. We also confirmed the transition states by frequency calculations and intrinsic reaction coordinate (IRC) analyses. The PESs and GFESs suggest spontaneous processes for the four isomers, of which the primary products are BH2(A)H (B) and its isomer BH2(B)H (A), the secondary product is BH2(C)H (C), and the tertiary product is BH2(D)H (D), all formed through adduct intermediates. Therefore, through the hydroboration reaction of C70, we could predict and design the site selectivity of C70 by controlling the energy barrier of the transition state in the second step of the reaction. This implies that we could selectively synthesize mainly BH2(B)H (A) isomers across the AB-[6,6]-ring fused bond and also design BH2(D)H(D) isomers across the DD-[5,6]-ring fused bond. Also, the calculations of formation rate constants can well simulate the experimental ratio of two C70H2 isomers by the hydrolysis of BH2(A)H(B), BH2(B)H(A), and BH2(C)H(C) products at room temperature.

Computational predictions of cocrystal formation: A benchmark study of 28 assemblies comparing five methods from high-throughput to advanced models

Cocrystals are assemblies of more than one type of molecule stabilized through noncovalent interactions. They are promising materials for improved drug formulation in which the stability, solubility, or biocompatibility of the active pharmaceutical ingredient (API) is improved by including a coformer. In this work, a range of density functional theory (DFT) and density functional tight binding (DFTB) models are systematically compared for their ability to predict the lattice enthalpy of a broad range of existing pharmaceutically relevant cocrystals. These range from cocrystals containing model compounds 4,4'-bipyridine and oxalic acid to those with the well benchmarked APIs of aspirin and paracetamol, all tested with a large set of alternative coformers. For simple cocrystals, there is a general consensus in lattice enthalpy calculated by the different DFT models. For the cocrystals with API coformers the cocrystals, enthalpy predictions depend strongly on the DFT model. The significantly lighter DFTB models predict unrealistic values of lattice enthalpy even for simple cocrystals.

Perovskite/silicon tandem solar cells with bilayer interface passivation

Two-terminal monolithic perovskite/silicon tandem solar cells demonstrate huge advantages in power conversion efficiency compared with their respective single-junction counterparts1,2. However, suppressing interfacial recombination at the wide-bandgap perovskite/electron transport layer interface, without compromising its superior charge transport performance, remains a substantial challenge for perovskite/silicon tandem cells3,4. By exploiting the nanoscale discretely distributed lithium fluoride ultrathin layer followed by an additional deposition of diammonium diiodide molecule, we have devised a bilayer-intertwined passivation strategy that combines efficient electron extraction with further suppression of non-radiative recombination. We constructed perovskite/silicon tandem devices on a double-textured Czochralski-based silicon heterojunction cell, which featured a mildly textured front surface and a heavily textured rear surface, leading to simultaneously enhanced photocurrent and uncompromised rear passivation. The resulting perovskite/silicon tandem achieved an independently certified stabilized power conversion efficiency of 33.89%, accompanied by an impressive fill factor of 83.0% and an open-circuit voltage of nearly 1.97 V. To the best of our knowledge, this represents the first reported certified efficiency of a two-junction tandem solar cell exceeding the single-junction Shockley-Queisser limit of 33.7%.

Dispersion leading potential energy surface of N2·NbN12-: Anion photoelectron spectroscopy and theoretical studies

In order to understand the dispersion interactions between molecules and to provide information about the potential energy surface of geometry evolutions, NbN12- and N2·NbN12- complexes were investigated by using photoelectron spectroscopy and ab initio calculations. The experimental adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of NbN12- were both measured to be 2.129 ± 0.030 eV. The experimental ADE and VDE of N2·NbN12- were measured to be 2.17 ± 0.05 and 2.23 ± 0.05 eV, respectively, which are slightly higher than those of NbN12-. The structures of NbN12-/0 were confirmed to be hexacoordinated octahedrons. The investigation of N2·NbN12- structures shows that it is stable for N2 to bind to the face or vertex site of octahedron NbN12-; the face-side-on structure has the lowest energy. The calculations based on symmetry-adapted perturbation theory suggest that the dispersion term is predominant and leads to the stability of N2·NbN12- complexes.

Machine learning-driven investigation of the structure and dynamics of the BMIM-BF4 room temperature ionic liquid

Room-temperature ionic liquids are an exciting group of materials with the potential to revolutionize energy storage. Due to their chemical structure and means of interaction, they are challenging to study computationally. Classical descriptions of their inter- and intra-molecular interactions require time intensive parametrization of force-fields which is prone to assumptions. While ab initio molecular dynamics approaches can capture all necessary interactions, they are too slow to achieve the time and length scales required. In this work, we take a step towards addressing these challenges by applying state-of-the-art machine-learned potentials to the simulation of 1-butyl-3-methylimidazolium tetrafluoroborate. We demonstrate a learning-on-the-fly procedure to train machine-learned potentials from single-point density functional theory calculations before performing production molecular dynamics simulations. Obtained structural and dynamical properties are in good agreement with computational and experimental references. Furthermore, our results show that hybrid machine-learned potentials can contribute to an improved prediction accuracy by mitigating the inherent shortsightedness of the models. Given that room-temperature ionic liquids necessitate long simulations to address their slow dynamics, achieving an optimal balance between accuracy and computational cost becomes imperative. To facilitate further investigation of these materials, we have made our IPSuite-based training and simulation workflow publicly accessible, enabling easy replication or adaptation to similar systems.

Dissociation Energies via Embedding Techniques

Due to the large number of interactions, evaluating interaction energies for large or periodic systems results in time-consuming calculations. Prime examples are liquids, adsorbates, and molecular crystals. Thus, there is a high demand for a cheap but still accurate method to determine interaction energies and gradients. One approach to counteract the computational cost is to fragment a large cluster into smaller subsystems, sometimes called many-body expansion, with the fragments being molecules or parts thereof. These subsystems can then be embedded into larger entities, representing the bigger system. In this work, we test several subsystem approaches and explore their limits and behaviors, determined by calculations of trimer interaction energies. The methods presented here encompass mechanical embedding, point charges, polarizable embedding, polarizable density embedding, and density embedding. We evaluate nonembedded fragmentation, QM/MM (quantum mechanics/molecular mechanics), and QM/QM (quantum mechanics/quantum mechanics) embedding theories. Finally, we make use of symmetry-adapted perturbation theory utilizing density functional theory for the monomers to interpret the results. Depending on the strength of the interaction, different embedding methods and schemes prove favorable to accurately describe a system. The embedding approaches presented here are able to decrease the interaction energy errors with respect to full system calculations by a factor of up to 20 in comparison to simple/unembedded approaches, leading to errors below 0.1 kJ/mol.

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.

Structural and energetic properties of cluster models of anatase-supported single late transition metal atoms: a density functional theory benchmark study

CONTEXT

Single-atom catalytic systems constitute an intriguing research topic due to their inherently different chemical behavior as compared to classic heterogeneous catalysts. In this study, cluster systems representing single late transition metal atoms adsorbed on anatase were constructed starting from previously generated periodic models and subjected to a density functional theory (DFT) benchmark study. The ability of different density functional approximations representing all rungs of the Jacob's Ladder classification to accurately describe bond lengths and adsorption energies was assessed for these clusters with the aim of revealing the functional that allows to retain the structural characteristics of the initial periodic system, while also delivering reliable energetics. In this regard, our results indicate that optimisation of the clusters with the meta-GGA functionals TPSS or RevTPSS provides the lowest mean unsigned error and root-mean-square deviations with respect to the periodic models. Moreover, these functionals and, to a slightly lesser degree, PW91 were also found to provide adsorption energies that are statistically the least deviating from the CCSD(T) reference data. More complex hybrid functionals appear to be performing less well.

METHODS

Cluster geometries were determined at the Kohn-Sham DFT level using the LANL2DZ basis set for the transition metals and the Pople 6-31G(d) basis set for O and H. The density functional approximations considered were SVWN, PBE, BP86, BLYP, PW91, TPSS, RevTPSS, M06L, M11L, B3LYP, PBE0, M06, M06-2X, MN15, ωB97X-D, CAM-B3LYP, M11, and MN12-SX. Reference adsorption energies of the metals on the support cluster were obtained at the CCSD(T)/LANL2TZ (transition metals)/6-311 +  + G(d,p)//RevTPSS/LANLD2DZ (transition metals)/6-31G*. Besides the above-mentioned functionals, energy calculations using the double-hybrid functionals, DSDPBEP86, PBE0-DH, and B2PLYP, were also performed. All adsorption energy calculations were carried out on the RevTPSS geometries.

Charge transfer characteristics in rhodopsin mimics during photoexcitation

To gain insights into the light-harvesting capabilities of the chromophores, it is essential to understand their molecular and electronic structures within their natural chemical or biological contexts. Rhodopsins display varied absorption characteristics due to the interaction between the chromophore retinal and its surrounding protein environments. In this study, we employed a quantum mechanics/molecular mechanics approach to examine a series of artificially designed rhodopsin mimics based on human cellular retinol acid binding protein 2 (hCRABP II). We elucidated the electron transfer within the all-trans protonated Schiff base upon light excitation, and our calculated absorption spectra show well consistency with the experimental result. Furthermore, the interaction mechanisms between the chromophore and the protein were investigated, and the relationship between the blueshifts and redshifts in the absorption spectra was analyzed. Our calculation demonstrates that the blueshifts and redshifts in the rhodopsin mimics correlate well with attractive (such as the hydrogen bonds or electrostatic interactions) and repulsive interactions (such as the steric effects) between the chromophore and the protein environment, respectively. These findings could provide hints for designing rhodopsin with absorption spectra at different wavelengths.

A formally exact theory to construct nonreactive forcefields using linear regression to optimize bonded parameters

This article derives theoretical foundations of force field functional theory (FFFT). FFFT studies topics related to the functional representation of nonreactive forcefields to achieve various desirable properties such as: (a) formal exactness of the forcefield's energy functional under certain conditions, (b) a formally exact ansatz separating the bonded potential energy from the nonbonded potential energy within a bonded cluster in a way that enables bonded parameters to be optimized using linear regression instead of requiring nonlinear regression, (c) the potential energy's continuous differentiability to various orders with respect to energetically accessible internal coordinate displacements within a subdomain defined by one electronic ground state, (d) forcefield design that guarantees the reference ground-state geometry is exactly reproduced as an equilibrium structure on the forcefield's potential energy landscape, (e) reasonably accurate and broadly applicable frugal model potentials, (f) computationally efficient embedded feature selection that identifies and removes unimportant forcefield terms, (g) well-designed methods to parameterize the forcefield from quantum-mechanically-computed and (optionally) experimental reference data, and (h) forcefields that approximately reproduce experimentally-measured properties. This article also introduces: (1) an angle-bending model potential that more accurately describes physical dynamics and is continuously differentiable to all orders with respect to internal coordinate displacements even when the bond angle is linear (i.e., θ = π (180°)) and (2) a first-principles-derived stretch potential that accurately describes short-range Pauli repulsion and the long-range bond dissociation energy. This new angle-bending potential gave good agreement to CCSD quantum-chemistry calculations for CaH2, CO2, H2O, HNO, Li2O, NO2, NS2, SF2, SiH2, and SO2 molecules. This new bond-stretch potential reproduced the first 12+ and 30+ vibrational energy levels of H2 and O2 molecules, respectively, within a few percent of experimental values. Studying the C-F bond stretch in C6F6 as an example, the new ansatz (item (b) above) reduced sensitivity of the optimized force constant's value to choice of nonbonded interaction parameters by an order of magnitude compared to the old ansatz. Normal mode analysis of optimized flexibility models for CO2, H2O, HNO, and SO2 molecules yielded vibrational transition frequencies within a few percent of experimental values. These results demonstrate advantages of this new approach.

Efficient Selective CO2 Composite Sorbent from Amino Acid Ionic Liquids and Silica Gel: 2H NMR Spectroscopy Provides Insight on the CO2-Binding Mechanism and in-Pore Microscopic Viscosity

A promising CO2 sorbent based on the [Emim][Gly] (1-ethyl-3-methylimidazolium glycinate)/silica gel composite has been studied. CO2 sorption experiments have shown that the optimum loading of [Emim][Gly] ionic liquid in silica gel is 40 wt.%. The 2-step process CO2 binding mechanism in [Emim][Gly] has been proposed based on the results of sorption experiments, 2H NMR spectroscopy and ab-initio calculations. The impact of CO2 on the microscopic viscosity and the dynamical melting of ionic liquid has been thoroughly investigated. 2H NMR spectroscopy has revealed that CO2 strongly binds cation and anion in [Emim][Gly], forcing them to move in a correlated fashion.

Frustrated Al/M Heterobimetallic Complexes (M = Cr, Mo, W) That Exhibit Both Lewis and Radical Pair Behavior

Exploration of new heterobinuclear Al/M combinations is relevant to contemporary strategies for cooperative bond activation. Here, we report the synthesis and characterization of six new Al/M heterobimetallic complexes (M = Cr, Mo, W) that exhibit end-on "isocarbonyl"-type Al─O═C═M bridges with metalloketene character rather than featuring Al─M─C≡O motifs with metal-metal bonding. The new compounds were characterized experimentally by nuclear magnetic resonance and infrared spectroscopies and theoretically using density functional theory, natural bond orbital, and quantum theory of atoms in molecules calculations. Factors influencing Al─O═C═M vs Al─M─C≡O isomerism were probed both experimentally and computationally. Crossover experiments between different group VI Al/M derivatives and regioselective epoxide ring opening indicate that the Al/M complexes act as masked frustrated Lewis pairs in solution under certain conditions. However, crossover experiments between group VI Al/M complexes and a previously studied Al-Fe complex, as well as computational modeling, imply that the same complexes can also reasonably act as masked frustrated radical pairs (FRPs). FRP reactivity with the group VI Al/M complexes was achieved under photochemical conditions, producing unsaturated metal-carbonyl dimers [(CpCr)2(CO)3]2- and [Mn2(CO)8]2-, which would otherwise be unstable under standard conditions but that are isolable here due to Al(III) coordination. The metal-metal bonding in these unsaturated metal-carbonyl dimers was also analyzed theoretically.

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.

Investigating Molecular Adsorption on Graphene-Supported Platinum Subnanoclusters: Insights from DFT + D3 Calculations

Platinum (Pt) subnanoclusters have become pivotal in nanocatalysis, yet their molecular adsorption mechanisms, particularly on supported versus unsupported systems, remain poorly understood. Our study employs detailed density functional theory (DFT) calculations with D3 corrections to investigate molecular adsorption on Pt subnanoclusters, focusing on CO, NO, N2, and O2 species. Gas-phase and graphene-supported scenarios are systematically characterized to elucidate adsorption mechanisms and catalytic potential. Gas-phase Pt n clusters are first analyzed to identify stable configurations and assess size-dependent reactivity. Transitioning to graphene-supported Pt n clusters, both periodic and nonperiodic models are employed to study interactions with graphene substrates. Strong adsorbate interactions predominantly occur at single top sites, revealing distinct adsorption geometries and stabilization effects for specific molecules on Pt6 clusters. Energy decomposition analysis highlights the paramount role of graphene substrates in enhancing stability and modulating cluster-adsorbate interactions. The interaction energy emerges as a critical criterion within the Sabatier principle, crucial for distinguishing between physisorption and chemisorption. Hybridization indices and charge density flow tendencies establish direct relationships with stabilization processes, underscoring graphene's influence in stabilizing highly reactive subnanoclusters. This comprehensive investigation provides critical insights into molecular adsorption mechanisms and the catalytic potential of graphene-supported Pt nanoclusters. Our findings contribute to a deeper understanding of nanocatalysis, emphasizing the essential role of substrates in optimizing catalytic performance for industrial applications.

Overcoming Challenges in O-Nitration: Selective Alcohol Nitration Deploying N,6-Dinitrosaccharin and Lewis Acid Catalysis

Nitrate esters hold pivotal roles in pharmaceuticals, energetic materials, and atmospheric processes, motivating the development of efficient synthesis routes. Here, we present a novel catalytic method for the synthesis of nitrates via the direct O-nitration of alcohols, addressing limitations of current traditional methods. Leveraging bench-stable and recoverable N,6-dinitrosaccharin reagent, our catalytic strategy employs magnesium triflate to achieve mild and selective O-nitration of alcohols, offering broad substrate scope and unprecedentedly large functional group tolerance (e.g. alkenes, alkynes, carbonyls). DFT mechanistic studies reveal a dual role of the magnesium catalyst in the activation of both the nitrating reagent and the alcohol substrate. They also unveil a barrierless proton transfer upon formation of a widely-accepted - yet elusive in solution - nitrooxonium ion intermediate. Overall, our work contributes to the development of mild, selective, and sustainable approaches to nitrates synthesis, with potential applications in drug discovery, materials science, and environmental chemistry.

A Density Functional Benchmark for Dehydrogenation and Dehalogenation Reactions on Coinage Metal Surfaces

The on-surface synthesis of low-dimensional organic nanostructures has been extensively investigated through both experimental and theoretical methods, particularly by density functional theory (DFT). However, the complex mixture of interactions often poses challenges within the DFT framework, and there is a knowledge-gap regarding how the choice of DFT approach affects the computed results. Here, five different approaches including vdW interactions, i. e., PBE+D3, PBE+vdWsurf, rev-vdWDF2, r2SCAN+rVV10 and BEEF-vdW, are employed to describe three prototypical on-surface reactions; dehydrogenation of benzene, debromination of bromobenzene, and deiodination of iodobenzene on the (111) facets of the coinage metals. Overall, rev-vdW-DF2 outperforms the other methods in describing benzene adsorption, whereas BEEF-vdW falls short. For dehydrogenation and debromination on Cu(111), all functionals except BEEF-vdW give reasonable activation energies compared to experiments. A similar trend is observed for Ag(111) and Au(111), with BEEF-vdW yielding significantly higher activation and reaction energies. For dehalogenation, all the five vdW approaches correctly capture the reactivity trend - Cu(111)>Ag(111)>Au(111) - and the expected hierarchy between bromobenzene desorption and carbon-bromine activation. Only BEEF-vdW fails to predict the faster kinetics of deiodination than the iodobenzene desorption. Our work forms a basis for evaluating density functionals in describing chemical reactions on surfaces.

A practical post-Hartree-Fock approach describing open-shell metal cluster-support interactions. Application to Cu3 adsorption on benzene/coronene

Current advances in synthesizing and characterizing atomically precise monodisperse metal clusters (AMCs) at the subnanometer scale have opened up fascinating possibilities in designing new heterogeneous (photo)catalysts as well as functional interfaces between AMCs and biologically relevant molecules. Understanding the nature of AMC-support interactions at molecular-level is essential for optimizing (photo)catalysts performance and designing novel ones with improved properties. Møller-Plesset second-order perturbation theory (MP2) is one of the most cost-efficient single-reference post-Hartree-Fock wave-function-based theories that can be applied to AMC-support interactions considering adequate molecular models of the support, and thus complementing state-of-the-art dispersion-corrected density functional theory. However, the resulting AMC-support interaction is typically overestimated with the MP2 method and must be corrected. The coupled MP2 (MP2C) scheme replacing the uncoupled Hartree-Fock dispersion energy by a coupled dispersion contribution, has been proven to describe accurately van-der-Waals (vdW)-dominated interactions between closed-shell AMCs and carbon-based supports. In this work, the accuracy of a MP2C-based scheme is evaluated in modelling open-shell AMC-cluster interactions that imply charge transfer or other strong attractive energy contributions beyond vdW forces. For this purpose, we consider the interaction of Cu3 with molecular models of graphene of increasing size (benzene and coronene). In this way, it is shown that subchemical precision (within 0.1 kcal mol-1) is achieved with the modified MP2C scheme, using the explicitly correlated coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)-F12] as a benchmark method. It is also revealed that the energy difference between uncoupled and coupled dispersion terms closely follows benchmark values of the repulsive intramonomer correlation contribution. The proposed open-shell MP2C-based approach is expected to be of general applicability to open-shell atomic or molecular species interacting with coronene for regions of the potential landscape where single-reference electronic structure descriptions suffice.

Supramolecular architecture of theophylline polymorphs, monohydrate and co-crystals with iodine: study from the energetic viewpoint

The regularities of crystal structure organization were thoroughly studied in all to date known polymorphic modifications of theophylline (THP) using an energetic approach. The monohydrate and a co-crystal of theophylline with one half equivalent of an iodine molecule were similarly investigated. The calculations of pairwise interaction energies have showed that the crystals studied can be divided into two groups according to their basic structural motifs: columnar-layered or columnar. The energetic approach also allows the role of different interactions in the crystal structure formation to be estimated. It was found that strong N-H⋯N, N-H⋯O hydrogen bonds and stacking interactions play the most important roles in polymorphic modifications of THP and the THP monohydrate. In the case of the co-crystal with iodine, N-H⋯O hydrogen bond participates in the dimeric building unit formation. However, instead of a stacking interaction the π⋯π interaction between carbonyl groups of neighboring molecules plays the highest role in the supramolecular architecture of this crystal. The lattice energies calculations in periodic conditions for polymorphic structures have shown that polymorph with the most anisotropic energetic structure may be considered as stable and all others forms metastable. In the polymorphic modification 1 of THP a zwitter-ionic resonance form is predominant, which affects significantly the solubility and the intermolecular interactions of this modification.