Unveiling next-generation organic photovoltaics: Quantum mechanical insights into non-fullerene donor-acceptor compounds

Organic photovoltaics (OPVs) have improved greatly in recent years in pursuit for efficient and sustainable energy conversion methods. Specifically, utilizing quantum chemistry approaches such as density functional theory (DFT), the electronic structures, energy levels, and charge transport characteristics of donor-π-acceptor (D-π-A) systems based on non-fullerene donor and acceptor molecules have been examined and synthesized. Non-fullerene acceptors offer several advantages over traditional fullerene-based materials, such as enhanced light absorption, modifiable energy levels, and reduced recombination losses. Quantum mechanical simulations are helpful in the design and development of these materials because they can accurately predict the energy level alignment, molecule interactions, and charge transport properties needed for the high-efficiency of OPVs. The research begins through the selection of electron-donating and electron-accepting non-fullerene polymeric molecules using the unique properties of non-fullerene derivatives and non-fullerene acceptors. The theory uses the B3LYP-D3 method with a 6-31+G (d,p) basis set. PY-IT is used as the reference molecule, and eight molecules PY-IT01-PY-IT08, has been created by changing the end caps of the acceptor units. The created compound has superior photovoltaic characteristics. Focus has been specifically given to the frontier molecular orbitals (FMOs), natural bond order (NBO) analysis, reorganization energies (RE), and absorption spectra in order to assess the viability of charge separation and efficient light absorption. Finally, the molecular electrostatic potential (MEP) analysis, transition density matrix (TDM) analysis, and improved open circuit voltage (Voc) all have been computed. The results of the findings provide new insight to design organic solar cells (OSCs) with improved photovoltaic and solar energy conversion capabilities, which has great potential for the future development of more dependable and efficient OSCs.

Structural characterization of cage clusters assembled borophene and implication for cathode electrocatalysts in Li-O2 batteries

The successful fabrication of quasi-freestanding bilayer borophene in experiments, combined with its superior metallic character, has propelled it to a rising star among two-dimensional materials, making it highly promising for applications in micro-electronic devices. Using first-principles calculations, we comprehensively explore and characterize cage cluster assembled borophenes through various methods for experimental references. The simulated scanning tunneling microscope (STM) images under diverse bias voltages exhibit distinct morphologies and closely associated with the partial densities of states (PDOS) of the surface boron atoms. High-resolution and large-scale simulated transmission electron microscope (TEM) images are investigated to detect the internal crystal structures, facilitating better identification of non-monolayer borophenes. The partial densities of states, electronic localization functions and Mulliken bond populations have been calculated to analyze the differences of morphology in STM and TEM images. Furthermore, simulated X-ray diffraction (XRD), Raman, and infrared (IR) spectra are characterized to further assist in distinguishing the phases of borophene. In light of ultrahigh stability and excellent metallic character, cluster assembled borophene of P3¯m1 symmetry act as cathode materials of Li-O2 battery with lower overpotential in oxygen evolution reaction (OER) than oxygen reduction reaction (ORR) processes. The overpotential is closely related to the adsorption strength of LiO2 and Li2O2 intermediates on surface of boron sheets. These theoretical results offer crucial guidance for the experimental identification of borophenes and suggest that the new type of cluster assembled systems might be suitable for the cathode materials of future Li-O2 batteries.

Computational detangling chalcogen elements substitutions associated ESDPT mechanism for oxazolinyl-substituted hydroxyfluorene derivatives

In view of the distinguished photochemical and photobiological characteristics of oxazolinyl-substituted hydroxyfluorene and its derivatives, herein, we mainly focus on probing into excited state behaviors of the novel 9,9-dimethyl-3,6-dihydroxy-2,7-bis(4,5-dihydro-4,4-dimethyl-2-oxazolyl) fluorene (Oxa-OH) derivatives. In light of the significant effects resulting from substituting oxygen elements, three Oxa-OH derivatives (i.e., Oxa-OO, Oxa-SS and Oxa-SeSe fluorophores) are considered in this work. For these three different fluorophores, we detangle the effects of atomic electronegativity and charge recombination related to oxygen elements in excited state double proton transfer (ESDPT) processes. Because of the low potential energy barriers, we confirm the ESDPT happens by the sequential type. Based on heterosubstituted Oxa-OS and Oxa-OSe compounds, we further verify the chalcogen atomic-electronegativity-regulated stepwise ESDPT mechanism. We sincerely wish our work could provide a theoretical reference for proving this novel mechanism of ESDPT experimentally.

Laser-Induced Alignment of Nanoparticles and Macromolecules for Coherent-Diffractive-Imaging Applications

Laser-induced alignment of particles and molecules was long envisioned to support three-dimensional structure determination using "single-molecule diffraction" with X-ray free-electron lasers [PRL 92, 198102 (2004)]. However, the alignment of isolated macromolecules has not yet been demonstrated also because quantitative modeling is very expensive. We computationally demonstrated that the alignment of nanorods and proteins is possible with a standard laser technology. We performed a comprehensive analysis on the dependence of the degree of alignment on molecular properties and experimental details, e.g., particle temperature and laser-pulse energy. Considering the polarizability anisotropy of about 150,000 proteins, our analysis revealed that most of these proteins can be aligned using realistic experimental parameters.

Rapid Octadecylphosphonic Acid Self-Assembled Monolayer Formation on Cu for Etch Inhibition: Characterizations Using Sum Frequency Generation Vibrational Spectroscopy

Self-assembled monolayers (SAMs) can be used to modify surface properties in a large area, which have wide applications ranging from corrosion inhibition, electronic device fabrication, oil/water separation, to biosensors. In industry, it is required to deposit a monolayer on copper substrate for etch inhibition within a short period of time. This study developed a simple method to satisfy such a need in industry. The SAM was deposited by using octadecylphosphonic acid (ODPA) solution. The quality of the prepared ODPA SAM on copper was compared to that of the SAM prepared using octadecanethiol (ODT) on copper. Sum frequency generation (SFG) vibrational spectroscopy was applied to characterize the deposited SAMs. It was found that ODPA SAMs prepared with 2 min of deposition time using ODPA solutions with concentrations of 0.05%, 0.1%, and 0.2% only have small numbers of gauche defects, with 80% or more methyl surface coverages compared to ODT SAMs. The deduced methyl group orientations of such ODPA SAMs are similar to that of the ODT SAM methyl groups. This study successfully demonstrated the feasibility of preparing relatively good quality ODPA SAMs on copper using a short deposition time.

Metal-ligand and hydrogen bonding in the active site of Fe(III)-, Mn(III)- and Co(III)-myoglobins

We investigated in this work the strength of metal-ligand bonding in complexes formed between Fe(III)-, Mn(III)- and Co(III)-myoglobin and methanol, water, nitrite, and azide, serving as neutral and ionic prototype ligands, for the ε and δ protonation forms of the myoglobin distal histidine. In total, 24 complexes and 12 associated gas phase models were investigated combining a QM/MM protocol with our local vibrational mode analysis at the PBE0/6-31G(d,p)/AMBER level of theory. According to our results, complexes with methanol and water ligands form weaker metal-ligand bonds than those with nitrite and azide ligands. Furthermore, the strength of the metal-ligand bonds depends on the protonation form of the distal histidine. Among the three metals investigated in this study, Fe, the metal found in native myoglobin, turned out to be the most versatile candidate, providing the broadest range of metal-ligand bond strengths. We also analyzed potential hydrogen bonds formed between the ligand and the distal histidine of the heme pocket. The ε tautomer of histidine forms weaker O⋯H type hydrogen bonds whereas the δ tautomer forms stronger N⋯H type hydrogen bonds. Overall, our findings identify the strength of both metal-ligand and hydrogen bonds (fully captured by our local vibrational mode analysis) as a key parameter determining the catalytic activity and function of myoglobins. This is particularly relevant when considering neutral versus ionic ligands and other metals such as Mn or Co as alternatives to Fe. The insights gained through our investigation offer valuable guidance for strategically fine-tuning existing artificial myoglobins and designing new, versatile variants. We hope that our QM/MM - local mode analysis protocol will become a valuable addition to the research community's toolkit.

Exploring Covalency in f-Element Complexes: Dithiocarbamate Ligands Reveal Differences Between Heavy Actinides and Lanthanides

Covalence in f-elements plays a pivotal role in distinguishing the fundamental properties of actinides and lanthanides. In this study, trivalent and tetravalent actinide (U-Fm) and lanthanide (Nd-Er) complexes with dithiocarbamate (S2CNH2-) ligands were systematically analyzed. Various methodologies were employed, notably Slater-Condon parameters, metrics in bond critical points (BCP) under the quantum theory of atoms in molecules (QTAIM) framework, and natural localized molecular orbitals (NLMOs). The multiconfigurational nature of the systems and the scalar relativistic and spin-orbit coupling effects were incorporated into the methods used. The findings reveal important differences in covalence between heavy actinides and lanthanides, where a higher covalence is observed in complexes containing metal ions with a higher oxidation state. According to QTAIM results, covalence in heavy actinides is energy-degeneracy driven rather than orbital overlap. Additionally, this suggests that donor atoms softer than oxygen, such as sulfur, promote covalence in heavy actinides, distinguishing them from their lanthanide counterparts and establishing them as softer Lewis acids.

What is the Exchange Repulsion Energy? Insight by Partitioning into Physically Meaningful Contributions

It is shown that the exchange repulsion energy, Exr, can be rationalized by partitioning the respective energy expression for two systems with Hartree-Fock orbitals into physically meaningful contributions. A division of Exr into a positive kinetic and a negative potential part is possible, but these contributions correlate only poorly with the actual exchange repulsion energy. A more meaningful partitioning is derived, where all kinetic energy contributions are collected in a term that vanishes for exact Hartree-Fock orbitals due to their stationarity conditions. The remaining terms can be distinguished into an exchange integral contribution as well as contributions to the repulsion energy with two, three and four orbital indices. The forms, relationships and absolute sizes of these terms suggest an intuitive partitioning of the exchange repulsion energy into Molecular Orbital Pair Contributions to the Exchange repulsion energy (MOPCE). Insight into the analytic form and quantitative size of these contributions is provided by considering the3 Σ u + ( 1 σ g 1 σ u ) ${^3 \Sigma _u^+ (1\sigma _g 1\sigma _u )}$ state of the H2 molecule, the water dimer, as well as an argon atom interacting with Cl2 and N2.

The role of water molecules in the dissociation of an electron-molecule contact pair

The hydrated electron, e-(aq), is a potent reducing agent and a prototypical quantum solute. Reactions of e-(aq) often involve a contact pair comprised of a molecule and electron that are hydrated within a single sphere. However, a molecular-level understanding of the solvent-driven coordinate that links the contact pair to the free dissociated e-(aq) remains elusive. Here, we study this coordinate by kinetically trapping representative metastable intermediates as gas-phase clusters and probing them using photoelectron spectroscopy. We apply this methodology to uracil-water anion clusters, where key intermediates are identified with supporting quantum chemical calculations. Just a single water molecule drives the parent molecule and non-valence electron apart, thereby inhibiting geminate recombination to form the more stable valence-bound uracil anion. The electron-water binding is akin to bare water cluster anions, highlighting the link to larger clusters and e-(aq). Our results provide a molecular-level view of quantum solute hydration and, more broadly, of how water-driven electron-transfer reactions proceed.

pts-Type Aluminoborate with Nonlinear Optical Properties

A noncentric 3D aluminoborate (ABO), NaCs2[AlB5O10]·HCOO·H2O (1), has been constructed through the solvothermal technique. The framework of 1 is formed by the alternation of AlO4 tetrahedra and B5O10 clusters, featuring 7 types of channels. 1 belongs to the "10,10-linkage", which features an unprecedented pts topology in the ABO field. The measurement of second-harmonic generation (SHG) shows that 1 displays an SHG value roughly 1.1 times that of KH2PO4 (KDP). The UV-vis diffuse reflectance spectrum suggests potential applications for 1 in the deep ultraviolet (DUV) field.

Lithium Borate-Squarate: An Organic-Inorganic Groups-Mixed Nonlinear Optical Crystal with Large Birefringence

To design new nonlinear optical (NLO) crystals efficiently, mixing two or more types of functional groups is a favored strategy. Herein, by combining two types of planar π-conjugate groups, triangular (BO3)3- and square (C4O4)2-, the new lithium borate-squarate composite NLO crystal Li2(C4O4)(H3BO3)(H2O)4·H3BO3 was synthesized, featuring a layered structure. This crystal exhibits a moderate second harmonic generation (SHG) response of 1.1 × KDP and a large birefringence of 0.267@1064 nm. Theoretical calculations demonstrate that the synergistic effect of the two types of groups is responsible for its optical performance. This work also enriches the currently scarce borate-squarate composite compound system.

Legion: A Platform for Gaussian Wavepacket Nonadiabatic Dynamics

Nonadiabatic molecular dynamics is crucial in investigating the time evolution of excited states in molecular systems. Among the various methods for performing such dynamics, those employing frozen Gaussian wavepacket propagation, particularly the multiple spawning approach, offer a favorable balance between computational cost and reliability. It propagates on-the-fly trajectories used to build and propagate the nuclear wavepacket. Despite its potential, efficient, flexible, and easily accessible software for Gaussian wavepacket propagation is less common compared to other methods, such as surface hopping. To address this, we present Legion, a software that facilitates the development and application of classical-trajectory-guided quantum wavepacket methods. The version presented here already contains a highly flexible and fully functional ab initio multiple spawning implementation, with different strategies to improve efficiency. Legion is written in Python for data management and NumPy/Fortran for numerical operations. It is created under the umbrella of the Newton-X platform and inherits all of its electronic structure interfaces beyond other direct interfaces. It also contains new approximations that allow it to circumvent the computation of the nonadiabatic coupling, extending the electronic structure methods that can be used for multiple spawning dynamics. We test, validate, and demonstrate Legion's functionalities through multiple spawning dynamics of fulvene (CASSCF and CASPT2) and DMABN (TDDFT).

Cavity-enhanced energy transport in molecular systems

Molecules are the building blocks of all of nature's functional components, serving as the machinery that captures, stores and releases energy or converts it into useful work. However, molecules interact with each other over extremely short distances, which hinders the spread of energy across molecular systems. Conversely, photons are inert, but they are fast and can traverse large distances very efficiently. Using optical resonators, these distinct entities can be mixed with each other, opening a path to new architectures that benefit from both the active nature of molecules and the long-range transport obtained by the coupling with light. In this Review, we present the physics underlying the enhancement of energy transfer and energy transport in molecular systems, and highlight the experimental and theoretical advances in this field over the past decade. Finally, we identify several key questions and theoretical challenges that remain to be resolved via future research.

Femtosecond Raman-induced Kerr effect spectroscopic study of the intermolecular dynamics in aqueous solutions of imidazolium hydrochloride, imidazole, sodium triazolide, and triazole: concentration dependence

In this study, we employed femtosecond Raman-induced Kerr effect spectroscopy to analyze the concentration-dependent intermolecular dynamics in positively or negatively charged aromatics and their neutral analogous aromatics (imidazolium hydrochloride (ImHCl), imidazole (Im), sodium triazolide (NaTr), and triazole (Tr)) in aqueous solutions at 293 K. We also measured their liquid properties, such as density, viscosity, and surface tension, at 293 K, and compared them with their dynamic properties. Furthermore, we performed the quantum chemistry calculations of the target aromatics and some clusters to elucidate their optimized structures, interaction energies, charge populations, and Raman-active normal modes. We characterized the Kerr transients over 2 ps using a triexponential function. The results revealed that the aqueous solutions' intermediate and slow relaxation time constants were linearly proportional to the viscosities. The slopes of the time constants to the viscosity of the aqueous ImHCl solutions were steeper than those of the aqueous Im solutions, whereas the slopes of the aqueous NaTr solutions were milder than those of the aqueous Tr solutions. These findings indicated that the charge of the aromatics in the aqueous solutions affected the coupling parameter between the solute and solvent in the orientational dynamics with different ways. The first moment (M1) of the low-frequency band (< 200 cm-1), coming from the intermolecular vibrations, in the difference spectra between the aqueous aromatic solutions and neat water shifted to the high-frequency region as the concentration increased. The M1 slope to the concentration for the aqueous ImHCl solutions was steeper than that for the aqueous Im solutions. Conversely, the concentration dependence of M1 for the aqueous NaTr solutions was similar to that for the aqueous Tr solutions. We used the local structures of the target aromatics based on the quantum chemistry calculations to rationally clarify their concentration-dependent intermolecular dynamics in the aqueous solutions.

Selective determination of metal chlorocomplexes in saline waters by magnetic ionic liquid-based dispersive liquid-liquid microextraction

In this work, we explore a new dispersive liquid-liquid microextraction (DLLME) method to selectively separate chemical species of Cd and Zn in saline waters. It is based on the use of the magnetic ionic liquid (MIL) methyltrioctylammonium tetrachloroferrate ([N1,8,8,8+][FeCl4-]), which allows an efficient and environmentally friendly extraction of the target species. In addition, the paramagnetic component in the MIL simplifies the separation step required in DLLME, allowing for fast separation and recovery of the extracted species with a magnet, without a centrifugation step. The optimum conditions for the separation by MIL-DLLME were 3.3 mg mL-1 MIL, sample pH = 8, and an extraction time of 30 min. Under these conditions, metal chlorocomplexes (99.7% and 81.0% of total metal concentration for Cd and Zn, respectively) were quantitatively separated, remaining the free cations in the aqueous samples. In a second step, the extracted metal species were back-extracted with 1 mol L-1 HNO3 and a re-extraction time of 15 min. For cadmium, this acidic solution separated the neutral complex CdCl2 (60.5%), while CdCl+ (21.5%) and CdCl3- (18.1%) remained in the organic phase. For Zn, the anionic complex ZnCl3- (17.3%) was retained by the organic reagent, while ZnCl2 (45.7%) and ZnCl+ (37.0%) were re-extracted by the nitric acid solution. The separation of the chemical species of metals along the three liquid phases used allowed their quantification in several samples of real seawater and a certified reference material.

Recent developments and applications of selected ion flow tube mass spectrometry (SIFT-MS)

Selected ion flow tube mass spectrometry (SIFT-MS) is now recognized as the most versatile analytical technique for the identification and quantification of trace gases down to the parts-per-trillion by volume, pptv, range. This statement is supported by the wide reach of its applications, from real-time analysis, obviating sample collection of very humid exhaled breath, to its adoption in industrial scenarios for air quality monitoring. This review touches on the recent extensions to the underpinning ion chemistry kinetics library and the alternative challenge of using nitrogen carrier gas instead of helium. The addition of reagent anions in the Voice200 series of SIFT-MS instruments has enhanced the analytical capability, thus allowing analyses of volatile trace compounds in humid air that cannot be analyzed using reagent cations alone, as clarified by outlining the anion chemistry involved. Case studies are reviewed of breath analysis and bacterial culture volatile organic compound (VOC), emissions, environmental applications such as air, water, and soil analysis, workplace safety such as transport container fumigants, airborne contamination in semiconductor fabrication, food flavor and spoilage, drugs contamination and VOC emissions from packaging to demonstrate the stated qualities and uniqueness of the new generation SIFT-MS instrumentation. Finally, some advancements that can be made to improve the analytical capability and reach of SIFT-MS are mentioned.

Barrierless reactions of C2 Criegee intermediates with H2SO4 and their implication to oligomers and new particle formation

The formation of oligomeric hydrogen peroxide triggered by Criegee intermediate maybe contributes significantly to the formation and growth of secondary organic aerosol (SOA). However, to date, the reactivity of C2 Criegee intermediates (CH3CHOO) in areas contaminated with acidic gas remains poorly understood. Herein, high-level quantum chemical calculations and Born-Oppenheimer molecular dynamics (BOMD) simulations are used to explore the reaction of CH3CHOO and H2SO4 both in the gas phase and at the air-water interface. In the gas phase, the addition reaction of CH3CHOO with H2SO4 to generate CH3HC(OOH)OSO3H (HPES) is near-barrierless, regardless of the presence of water molecules. BOMD simulations show that the reaction at the air-water interface is even faster than that in the gas phase. Further calculations reveal that the HPES has a tendency to aggregate with sulfuric acids, ammonias, and water molecules to form stable clusters, meanwhile the oligomerization reaction of CH3CHOO with HPES in the gas phase is both thermochemically and kinetically favored. Also, it is noted that the interfacial HPES- ion can attract H2SO4, NH3, (COOH)2 and HNO3 for particle formation from the gas phase to the water surface. Thus, the results of this work not only elucidate the high atmospheric reactivity of C2 Criegee intermediates in polluted regions, but also deepen our understanding of the formation process of atmospheric SOA induced by Criegee intermediates.

Indoor bioaerosols and asthma: Overview, implications, and mitigation strategies

Aerosolized particles with a biological origin are called bioaerosols. Bioaerosols from plants, animals, fungi, bacteria, and viruses are an important class of environmental exposures that are clinically relevant to asthma. However, there are important differences in the pathways by which various bioaerosols affect asthma. Additionally, differences in individual susceptibility to different bioaerosols affect exposure reduction and mitigation strategies. Strategies to reduce exposures to potential triggers of asthma are routinely considered as part of standard clinical care and asthma management guidelines. Ventilation standards in buildings may reduce bioaerosol exposure for everyone, but they are not necessarily designed specifically to protect patients with asthma. Direct measurement of a bioaerosol is not generally necessary for practical applications where the relevant source of the bioaerosol has been identified. Different types of bioaerosols can be controlled with similar strategies that prioritize source control (eg, reducing resuspension, integrated pest management, controlling moisture), and these can be supplemented by enhancing air filtration. The goal of this review is to summarize the latest information on bioaerosols, including allergens, fungi, bacteria, and viruses, that have been associated with adverse asthma outcomes and to discuss mitigation options.

Gas-phase, conformer-specific infrared spectra of 3-chlorophenol and 3-fluorophenol

Conformational isomerism of phenol derivatives has been a subject of extensive spectroscopic study. Combining the capabilities of the widely tuneable infrared free-electron laser FELIX with molecular beam technologies allows for revisiting existing data and gaining additional insights into far-IR spectroscopy of halogenated phenols. Here we present conformer-resolved infrared spectra of the syn and anti conformers of 3-chlorophenol and 3-fluorophenol recorded via IR-UV ion-dip spectroscopy. The experimental work is complemented by density functional theory calculations to aid in assignment of the observed bands. The experimental spectra for the two conformers of each molecule show overall a great similarity, but also include some distinct conformer-specific bands in the spectral range investigated. Our spectra confirm previously reported OH torsional mode frequencies for the syn and anti conformers of 3-chlorophenol (3CP) at 315 cm-1, (Manocha et al., J. Phys. Chem., 1973, 77, 2094) but reverse their assignment of the 311 and 319 cm-1 bands for 3-fluorophenol. 1D torsional mode calculations were performed for 3CP to help assign possible OH torsion overtones.

MOLPIPx: An end-to-end differentiable package for permutationally invariant polynomials in Python and Rust

In this work, we present MOLPIPx, a versatile library designed to seamlessly integrate permutationally invariant polynomials with modern machine learning frameworks, enabling the efficient development of linear models, neural networks, and Gaussian process models. These methodologies are widely employed for parameterizing potential energy surfaces across diverse molecular systems. MOLPIPx leverages two powerful automatic differentiation engines-JAX and EnzymeAD-Rust-to facilitate the efficient computation of energy gradients and higher-order derivatives, which are essential for tasks such as force field development and dynamic simulations. MOLPIPx is available at https://github.com/ChemAI-Lab/molpipx.

The universal vibrational dynamics of water bound to tertiary amines: more than just Fermi resonance

Amines with three alkyl substituents are shown to be strongly microsolvated by water molecules, unless the steric hindrance of the alkyl groups overcompensates the increase in basicity of the N atom by alkylation. The hydrogen bond interaction of the first water molecule is so strong that the softened OH vibration shares its intensity with up to three largely dark states involving quanta of intramolecular bending or stretching and intermolecular stretching vibration. A combination of FTIR, Raman, isotope and chemical substitution spectroscopy in supersonic jet expansions establishes the existence, character and extent of the underlying anharmonic coupling. The observed resonance pattern is remarkably systematic and allows to extract physically plausible, effective normal mode coupling constants which are relevant for the initial energy flow out of the excited OH oscillator. A remaining ambiguity in the coupling pattern for the weakest transition invites detailed anharmonic quantum dynamics studies, but it still allows for robust deperturbed positions of the uncoupled oscillators for 8 amine monohydrates, which are valuable as experimental benchmarks for databases and for the training phase of theory blind challenges on microhydration. The more isolated hydrogen-bonded OH stretching vibration of a second water molecule is also assigned to widen the scope of a future theory challenge addressing the wavenumber of hydrogen-bonded OH groups. Such blind challenges thus remain accessible not only to fully anharmonic, but also to scaled harmonic and machine learning approaches which may try to average over the anharmonic details.

Simulating Vibrational Dynamics on Bosonic Quantum Devices

Bosonic quantum devices, which utilize harmonic oscillator modes to encode information, are emerging as a promising alternative to conventional qubit-based quantum devices, especially for the simulation of vibrational dynamics and spectroscopy. We present a framework for digital quantum simulation of vibrational dynamics under anharmonic potentials on these bosonic devices. In our approach, the vibrational Hamiltonian is decomposed into solvable fragments that can be used for Hamiltonian simulation on currently available bosonic hardware. Specifically, we have extended the Cartan subalgebra approach [Yen, T.C.; Izmaylov, A. F. PRX Quantum 2, 2021; 040320]- a method for decomposing quantum Hamiltonians into solvable parts- to bosonic operators, enabling us to construct anharmonic Hamiltonian fragments that can be efficiently diagonalized using Bogoliubov transforms. The approach is tested using a simulation of tunneling dynamics in a model two-dimensional double-well potential and calculations of vibrational eigenenergies for small molecules. Our fragmentation scheme provides a new approach for digital quantum simulations on bosonic quantum hardware for multimode anharmonic vibrational dynamics.

Theoretical Study of Spectroscopy and Photodynamics of Decatetraene as a Representative Dimethylated Polyene

The photodynamics and UV spectroscopy of decatetraene following excitation to the bright 1Bu state are studied theoretically, based on ab initio computations of the underlying potential energy (PE) surfaces. Both photophysical and photochemical aspects are investigated. The former involves smaller amplitude displacements, and - in addition to determining multidimensional PE surfaces - also a quantal treatment of the ensuing nuclear dynamics. The inclusion of the 1Bu-2Ag vibronic interaction allows to compute the vibrational structure of the 1Ag-1Bu UV spectral band and the femtosecond 1Bu-2Ag internal conversion (population transfer). The results are compared with analogous features of octatetraene and octatriene. The photochemical aspects involving larger-amplitude displacements are investigated from a quantum-chemical point of view, focusing on the stationary points and the seams of conical intersections that are involved. A comparison of decatetraene with octatetraene reveals the contrasting features of their 2Ag and 1Bu state minima, where the latter is more stable in the dimethylated system. The small barrier connecting these two states lies between 0.06 and 0.11 eV. The nonradiative decay channels originating from these minima are characterized by comparatively higher barriers in decatetraene and influence the outcome of the radiative processes in a different manner in comparison to that of octatetraene.

Theoretical monitoring of aromaticity induction from noble gases to Borole structure

Density functional theory (DFT) calculations were conducted to examine the inductive charge transferring from noble gas (Ng) atoms to borole structure. The calculations indicate that all noble gas atoms especially heavier ones can induce charge to the B atom of the borole structure and decrease its antiaromaticity nature. In-depth, Ng∙∙∙B interaction analyses reveal that the noble gas atoms serve as donor fragments in the formation of Ng∙∙∙B donor-acceptor non-covalent interactions. It has been demonstrated that noble gas atoms can successively form aromaticity induction via interacting with B atom in the borole structure.

Overview of Developments in the MRCC Program System

mrcc is a versatile suite of quantum chemistry programs designed for accurate ab initio and density functional theory (DFT) calculations. This contribution outlines the general features and recent developments of the package. The most popular features include the open-ended coupled-cluster (CC) code, state-of-the-art CC singles and doubles with perturbative triples [CCSD(T)], second-order algebraic-diagrammatic construction, and combined wave function theory-DFT approaches. Cost-reduction techniques are implemented, such as natural orbital (NO), local NO (LNO), and natural auxiliary function approximations, which significantly decrease the computational demands of these methods. This paper also details the method developments made over the past five years, including efficient schemes to approach the complete basis set limit for CCSD(T) and the extension of our LNO-CCSD(T) method to open-shell systems. Additionally, we discuss the new approximations introduced to accelerate the self-consistent field procedure and the cost-reduction techniques elaborated for analytic gradient calculations at various levels. Furthermore, embedding techniques and novel range-separated double-hybrid functionals are presented for excited-state calculations, while the extension of the theories established to describe core excitations and ionized states is also discussed. For academic purposes, the program and its source code are available free of charge, and its commercial use is also facilitated.

High-Resolution Photoelectron Imaging of Cryogenically-Cooled B8- and CB7- Clusters: From Borozene to Carborozene

The closed-shell B73-, B82-, and B9- species are recognized recently to be electron-precise molecular wheels with three delocalized π-bonds reminiscent of benzene, giving rise to the concept of "borozene". The B82- borozene is especially stable because the B7 ring has the right size to host a central boron atom. Replacing a B atom by C yields a highly stable closed-shell CB7-, which is isoelectronic to B82-. Here we use high-resolution cryogenic photoelectron imaging to probe B8- and CB7-, revealing rich vibrational information about B8 and CB7 and the vibrational modes responsible for the structure changes from the anions to the neutrals. Surprisingly, a minor isomer is also observed for B8- and found to be due to Jahn-Teller splitting, analogous to the Jahn-Teller effect in the C6H6+ benzene cation. The transformation from the B82- borozene to the CB7- carborozene is similar to that from the B12H122- borane to the CB11H12- carborane.

Influence of Water on the NO3 + HO2 Reaction

The reaction between NO3 and HO2 is one of the most important reaction in nighttime atmospheric chemistry. There are two pathways for this reaction: one leading to the formation of HNO3, and the other resulting in the formation of the OH radical. Recent experimental and theoretical studies suggest that this reaction occurs through only the OH radical pathway. In this work, we have investigated the fate of this reaction in the presence of water using high-level quantum chemical and kinetics calculations over the temperature range of 213-400 K. Our investigation suggests that even in the presence of a water monomer, the reaction predominantly produces OH radicals.

Dynamics Study of the CaC (X3∑-) + C(3Pg) → Ca+C2 (∑v) Reaction: Based on a Full-Dimensional Neural Network Potential Energy Surface of CaC2

The CaC2 molecule, as an interstellar species that has already been detected, has attracted significant attention. To date, studies on the potential energy surface (PES) and the reaction dynamics of CaC2 are largely lacking. In this work, ab initio energy values were obtained for 3877 configurations using the icMRCI+Q method, and these energies were subsequently fitted using a neural network approach. During parameter optimization, the trust region framework (TRF) method, which has superior performance compared to the previously used Levenberg-Marquardt (LM) method, was used. The root-mean-squared error (RMSE) for both the training and testing sets meets the requirement for chemical accuracy (error less than 1 kcal/mol). Using the neural network PES, we identified one stable structure and two metastable structures for the ground state (X̃1A') of CaC2. The stable structure is T-shaped, while the two metastable structures are linear. The potential well depths of the stable structure and the two metastable structures are -10.98, -9.75, and -4.70 eV, respectively. Based on the obtained full-dimensional neural network PES, we investigated the CaC(X3Σ-) + C(3Pg) → Ca + C2 (Σv) reaction dynamics under different initial conditions. Under the condition that all other parameters remain unchanged, the reaction cross section and rate constant were found to be largest when the initial condition was v = 0 and j = 0. These findings indicate that the reaction rate is fastest when the CaC molecule is in its ground state.

Dual-Level Parametrically Managed Neural Network Method for Learning a Potential Energy Surface for Efficient Dynamics

A general difficulty with machine-learned potential energy surfaces is their unreliability in regions with little or no training data. The goal of the present work is to remedy this by a low-cost method for incorporating well understood features of potential energy surfaces into an efficient data-driven machine learning algorithm. Our focus is on regions where conventional surface fitting does not need large amounts of accurate data, in particular, geometries with large separations of subsystems-where it is well recognized that the potential should reach its asymptotic form-and geometries with very close atoms-where the potential should be repulsive enough to prevent trajectories from reaching classically inaccessible regions but need not be highly quantitative. The new method involves a neural network (NN) with a parametrically managed activation function (PMAF) and two levels of electronic structure, a higher level (HL) and a lower level (LL). The resulting NN is called a dual-level parametrically managed neural network (DL-PMNN). For the present example, the HL is an accurate density functional method (CF22D/may-cc-pVTZ), and the LL is an inexpensive density functional method (MPW1K/MIDIY). We use the LL to ensure correct behavior of the potential at large and small distances; the goal is to reach HL accuracy for dynamics without making HL calculations in regions where the LL can guide the fit. To illustrate the new method, we fit the potential energy surface for dissociation of the S-H bond of ortho-fluorothiophenol in the ground electronic state, and we show that the method yields a good fit and efficient trajectory calculations without crashes.

Bulk Anion Recognition Kinetically Holds Back Interfacial Adsorption

The competition between bulk and interfacial phenomena underlies many key processes in complex chemical phenomena and transport. While competitive processes are often framed in a thermodynamic context, opportunities to leverage transient species found away from equilibrium can provide a kinetic handle to achieve unconventional reaction outcomes. In this work, we outfit an iminoguanidinium headgroup capable of selective SO42- complexation with alkyl tails of varying complexity to probe competitive bulk and interfacial reaction pathways and tune kinetic pathways for selective chemical separations. Using sum frequency generation (SFG) vibrational spectroscopy we unexpectedly find that adsorption of ligands to the air-aqueous interface was dramatically slowed down for species with increasingly hydrophobic tails. Underlying this phenomenon, we show that the formation of bulk colloidal species with differing propensities for SO42- inhibited surface adsorption via a kinetic bottleneck in the exchange of molecular extractants with colloidal aggregates. This kinetic effect could open up avenues to access unconventional selectivity via complexation of strongly coordinating species in the bulk phase, allowing for more weakly coordinating species to transport via interfacial mechanisms. This work broadly probes nonequilibrium phenomena in chemical separations that arise through unexpected interfacial events that are neglected in traditional equilibrium descriptions.

Trapping intermediates of the NO2 hydrolysis reaction on ice

Using molecular beam methods, a mixture of stable NO2, O2NNO2, and up to 30% relative abundance of metastable t-ONONO2, a potential heterogeneous hydrolysis reaction intermediate, was prepared by heating the quasi-effusive molecular beam nozzle to 600 K. The chemical speciation of hot nitrogen dioxide vapours was established using reflection-absorption IR spectroscopy (RAIRS) at very high (i.e., 1 : 1000) dilution by exploiting selective enhancement in absorbance features due to electric field standing waves (EFSW). Mode-selective shifts in the NO stretching vibrational frequencies of these species are observed upon their adsorption to the surface of amorphous solid water (ASW) at 40 K compared to their value in a crystalline solid argon matrix. Their sensitivities to hydration were assessed by computational chemistry methods using clusters of up to ten water molecules. This revealed that the shifts in the vibrational frequency of the terminal NO stretching mode and of the asymmetric ONO stretching mode of the terminal -NO2 group of t-ONONO2 upon its adsorption onto the surface of ASW signal that its ON-ONO2 bond is significantly polarized. Upon thermal annealing of the sample to 130 K, spectral signatures attributed to adsorbed nitrate anions can be observed suggesting that the activation barrier to heterogenous hydrolysis of the ON+·-ONO2 zwitterionic reaction intermediate is sufficiently small to be overcome at cryogenic temperatures. Facile NO2 hydrolysis on aqueous interfaces could contribute to their acidification and to elevated nitrous acid emission fluxes to the lower troposphere.

Photoswitching Molecules Functionalized with Optical Cycling Centers Provide a Novel Platform for Studying Chemical Transformations in Ultracold Molecules

A novel molecular structure that bridges the fields of molecular optical cycling and molecular photoswitching is presented. It is based on a photoswitching molecule azobenzene functionalized with one and two CaO- groups, which can act as optical cycling centers (OCCs). This paper characterizes the electronic structure of the resulting model systems, focusing on three questions: (1) how the electronic states of the photoswitch are impacted by a functionalization with an OCC; (2) how the states of the OCC are impacted by the scaffold of the photoswitch; and (3) whether the OCC can serve as a spectroscopic probe of isomerization. The experimental feasibility of the proposed design and the advantages that organic synthesis can offer in the further functionalization of this molecular scaffold are also discussed. This work brings into the field of molecular optical cycling a new dimension of chemical complexity intrinsic to only polyatomic molecules.

Connecting the complexity of stereoselective synthesis to the evolution of predictive tools

Synthetic methods have seemingly progressed to an extent where there is an apparent and increasing need for predictive models to navigate the vast chemical space. Methods for anticipating and optimizing reaction outcomes have evolved from simple qualitative pictures generated from chemical intuition to complex models constructed from quantitative methods like quantum chemistry and machine learning. These toolsets are rooted in physical organic chemistry where fundamental principles of chemical reactivity and molecular interactions guide their development and application. Here, we detail how the evolution of these methods is a successful outcome and a powerful response to the diverse synthetic challenges confronted and the innovative selectivity concepts introduced. In this review, we perform a periodization of organic chemistry focusing on strategies that have been applied to guide the synthesis of chiral organic molecules.

Computational studies on the clusters of HONO•(H2O)n(n = 1-7): structures and enthalpy of formation

CONTEXT

Nitrous acid (HONO) is often associated with many air pollution events, such as the ozone hole, acid rain, and human health. Herein, we performed the theoretical studies on the structures and enthalpy of formation for the hydrated clusters HONO∙(H2O)n(n = 1-7). Two different isomers of HONO including cis-HONO and trans-HONO were studied. Minima structures of trans-HONO∙(H2O)n(n = 1-7) and cis-HONO∙(H2O)n(n = 1-7) clusters containing forty-eight and twenty-one were found, respectively. The hydrogen-bonded interactions between HONO and water molecules in HONO∙(H2O)n(n = 1-7) clusters were analyzed. Enthalpies of the formation of the most stable isomers of trans-HONO∙(H2O)n(n = 1-7) and cis-HONO∙(H2O)n(n = 1-7) clusters are predicted theoretically. These results can provide a new understanding of the atmospheric circulation of HONO.

METHODS

Geometric structures and vibrational frequencies of the HONO∙(H2O)n(n = 1-7) clusters were investigated by using the QCISD(T)/6-311 + G(3df,2p)//M06-2X/6-311 + G(3df,2p) method. Enthalpies of formation of the global minimal isomers of the HONO∙(H2O)n(n = 1-7) clusters were calculated at the CBS-QB3 level of theory. Atoms in molecules (AIM) theory was applied to the analysis of hydrogen-bonded interactions among the HONO∙(H2O)n(n = 1-7) clusters.

Two-dimensional isotopic shifts for steroid isomer delineation with high-resolution cyclic ion mobility separations

Recently, the use of mass distribution-based isotopic shifts in high-resolution ion mobility spectrometry-mass spectrometry-based separations have enabled isomer delineation by measuring the relative arrival times of their heavy and light isotopologues. However, all previous efforts to induce such shifts have focused solely on the introduction of one type of isotopic substitution for a given molecule or isomer set. Herein, for the first time, we present a two-dimensional isotopic labeling strategy where two unique derivatizations are performed on various steroid isomer molecules to induce two distinct isotopic shifts and thus simultaneously measure them in a single ion mobility separations experiment. Derivatization strategies were chosen to target two specific functional groups in these steroids (i.e., hydroxyl and carbonyl), and heavy-labeled versions of the derivatizing reagents were used to induce isotopic shifts at each of these positions. We found that isotopic shifts were orthogonal to one another, diagnostic for certain steroid isomers, and that the simultaneous analysis of two different isotopic shifts was necessary for complete characterization of each steroid isomer set. We envision this multidimensional isotopic shift strategy as a new method for delineating amongst isomeric molecules, especially those with several different functional groups causing their isomerism.

Enabling Accurate and Large-Scale Explicitly Correlated CCSD(T) Computations via a Reduced-Cost and Parallel Implementation

Parallel algorithms to accelerate explicitly correlated second-order Mo̷ller-Plesset (MP2) and coupled-cluster singles and doubles with perturbative triples [CCSD(T)] calculations and benchmarks on extended molecular systems are reported. A hybrid Open Multi-Processing (OpenMP)/Message Passing Interface (MPI) parallel approach is used to distribute the computational load among processor cores and compute nodes. The intermediates at both the MP2 and the CCSD(T) levels are expressed in a density fitting formalism, using only three-index quantities to decrease the amount of data to be stored and communicated. To further reduce compute time, the frozen natural orbital, the natural auxiliary function, and the natural auxiliary basis schemes are implemented in a hybrid parallel manner. The combination of these three approximations and our recent size-consistent explicitly correlated triples correction with the new hybrid parallelization offers a unique accuracy-over-cost performance among explicitly correlated CC methods. Our comprehensive benchmarks demonstrate excellent parallel scaling of the cost-determining operations up to hundreds of processor cores. As demonstrated on the noncovalent interaction energy of the corannulene dimer, highly accurate explicitly correlated CCSD(T) calculations can be carried out for systems of 60 atoms and 2500 orbitals, which were beyond computational limits without local correlation approximations. This enables various applications, such as benchmarking of or, for certain size ranges, replacing local CCSD(T) or density functional methods as well as the further advancement of robust thermochemistry protocols designed for larger molecules of ca. 20-50 atoms.

Ab Initio Molecular Dynamics Simulation Study on the Thermal Decomposition Mechanism of Two F-Containing Compounds: 3,3,7,7-Tetrakis(difluoramino)-octahydro-1,5-dinitro-1,5-diazocine (HNFX) and 1,3,5-Trinitro-2,2-bis(trifluoromethyl)-1,3,5-triazinane (TNBFT)

F-containing explosives with additional F atoms compared to traditional CHON ones should contain a more complex decomposition mechanism. Nevertheless, understanding the mechanism and effect of F-containing groups on stability remains limited. This study investigates the thermal decomposition mechanisms of two typical F-containing compounds, 3,3,7,7-tetrakis(difluoramino)-octahydro-1,5-dinitro-1,5-diazocine (HNFX) and 1,3,5-trinitro-2,2-bis(trifluoromethyl)-1,3,5-triazinane (TNBFT), using ground-state ab initio molecular dynamics simulations and compares them with RDX. The results show that HNFX decomposes from the partition of -NF2 to form NF3 and HF at 1500 K and above 2000 K, respectively, while TNBFT undergoes the concerted H transfer and HONO elimination at 1500 K and the N-NO2 bond cleavage at relatively high temperatures. Additionally, HF and fluorocarbons, as the primary fluorinated products, lower the yields of H2O and CO2 compared to RDX, but they can act as oxidizers in combustion with Al particles. Moreover, it is found that F-containing groups significantly weaken the bonds nearby and the total molecular stability. Based on our bond strength analysis and simulation results, the reported experimental confirmation of the thermal stability of HNFX may be questionable. This insight is expected to deepen the thermal decomposition mechanisms of F-containing explosives and guide the design of high-performance composites thereof.

Nonadiabatic Coupling Dictates the Site-Specific Excited-State Decay Pathways of Fluorophenols

In this paper, a combined photophysical and electronic structure theory study demonstrating a remarkable site-specific fluorine substitution effect on the excited-state dynamics of monofluorophenols has been presented. The S1 ← S0 electronic origin band of phenol is shifted to a longer wavelength for para substitution, but to shorter wavelengths for ortho and meta substitutions. The observed sequence of excitation wavelengths of 2-fluorophenol (2FP) < 3-fluorophenol (3FP) < phenol < 4-fluorophenol (4FP) is consistent with the transition energies predicted by TDDFT/CAMB3LYP/6-311++G(d,p) and CASSCF(8,8)/Dunning cc-pVDZ theoretical methods. The most notable contrast of excited-state dynamics is revealed in the different features of the fluorescence spectra; the fluorescence yield of 4FP is almost 6 times larger compared to that of 3FP and the spectral bandwidth of 2FP is nearly 1.5 times larger than that of 4FP. Electronic structure calculation predicts a low-energy S1/S0 conical intersection (CI) near the 1ππ* minimum with respect to the prefulvenic vibronic mode of the aromatic ring, and the energetic location of this CI is altered with the substitution site of the fluorine atom. The predicted energy barrier to this prefulvenic CI is smallest for 3FP but largest for 4FP, leading to a facilitated nonradiative electronic relaxation of the former (3FP), and emission occurs with a much diminished fluorescence intensity.

MBX V1.2: Accelerating Data-Driven Many-Body Molecular Dynamics Simulations

The MBX software provides an advanced platform for molecular dynamics simulations, leveraging state-of-the-art MB-pol and MB-nrg data-driven many-body potential energy functions. Developed over the past decade, these potential energy functions integrate physics-based and machine-learned many-body terms trained on electronic structure data calculated at the "gold standard" coupled-cluster level of theory. Recent advancements in MBX have focused on optimizing its performance, resulting in the release of MBX v1.2. While the inherently many-body nature of MB-pol and MB-nrg ensures high accuracy, it poses computational challenges. MBX v1.2 addresses these challenges with significant performance improvements, including enhanced parallelism that fully harnesses the power of modern multicore CPUs. These advancements enable simulations on nanosecond time scales for condensed-phase systems, significantly expanding the scope of high-accuracy, predictive simulations of complex molecular systems powered by data-driven many-body potential energy functions.

Real-Time Analysis of CO2 Reduction Product Distribution by Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry

Understanding the transient physicochemical properties at the cathode/catholyte interface is a prerequisite to shedding light on the complex electrochemical CO2 reduction reaction (CO2RR) mechanism as well as to steering the product distribution toward precise CO2 valorization. Herein, we report a flow-cell-based synchrotron vacuum ultraviolet photoionization mass spectrometric approach to resolve the dynamic interfacial species evolution during Cu-catalyzed CO2RR. By optimizing the photoionization energy, characteristic molecular ions of 8 volatile reduction products, together with the CO2 reactant, have been precisely captured for both potential step and linear sweep voltammetric measurements. The soft photoionization with fine-tuned energy avoids complicated mass signal deconvolution in conventional quadrupole mass spectrometry with electron impact ionization, while orders of magnitude higher temporal resolution has been demonstrated for this spectroelectrochemical technique as compared to headspace gas chromatography analysis on gaseous effluent from the CO2RR, providing a feasible way to resolve complex interfacial (electro)chemistry in real time.

Mass-Selected Infrared Photodissociation Spectroscopic and Theoretical Insights into Nitrobenzene Dimer Anion Tagged by Argon

The nitrobenzene dimer anion, NB2-, tagged with argon in the gas phase was successfully generated by using a collinear tandem time-of-flight mass spectrometer equipped with a supersonic ion source. Precise characterization was achieved through infrared photodissociation (IRPD) spectroscopy combining with theoretical calculation. Nine distinct absorptions were observed. The optimized structures of NB2(Ar)- were categorized into three types of isomers, including double-hydrogen-bonded (DHB), T-shaped (TS), and antiparallel π-π stacking (APS) isomers. The vibrational analysis indicated that the calculated spectrum of the APS isomer (e) exhibited better agreement with the experimentally observed spectrum than that of the lowest energy DHB isomer (a). Singly occupied molecular orbitals (SOMOs) and natural population analysis (NPA) confirmed that the negative charge in NB2(Ar)- was predominantly localized on one NB unit carrying a charge of -0.932 e, closely resembling a single electron charge. The other NB unit exhibited a minimal negative charge of -0.069 e, and Ar had a charge of 0.001 e. This distribution of charge suggests that NB2- can be viewed as a molecule-anion species, which consists of two separate frameworks: one neutral NB and one anionic NB framework. Energy decomposition analysis (EDA) further revealed that the stabilization of the APS isomer resulted from a nearly equal contribution of dispersion and electrostatic forces. However, for the DHB isomer, only the electrostatic interaction emerged as the primary stabilizing force.

Investigation of Vibrational Cooling in a Photoexcited Dichloro-Ruthenium Charge Transfer Complex Using Transient Electronic Absorption Spectroscopy

Vibrational cooling of molecules in excited electronic states is ubiquitous in photochemical reactions in solution but challenging to infer in time-resolved electronic absorption experiments. We report the ultrafast photophysics of cis-dichlorobis(2,2'-bipyridine)ruthenium(II), Ru(bpy)2Cl2, a precursor molecule commonly utilized in synthetic modifications of a vast array of ruthenium complexes. Femtosecond time-resolved electronic absorption spectroscopy is used to track an ultrafast spectral narrowing of the excited-state absorptions at 475 nm (21,050 cm-1) and 505 nm (19,800 cm-1) due to the reduced ligand in the photoexcited molecular complex. These sharp features, which overlap with a broader ground-state bleach spanning 450 nm (22,220 cm-1) to 600 nm (16,670 cm-1), evolve rapidly with time constants of 16 ± 5, 15 ± 3, and 18 ± 2 ps, respectively, for ligand-centered (π → π*, 266 nm) and charge-transfer (t2 → π*, 400 and 550 nm) excitations and constitute a direct signature of picosecond vibrational cooling.

Impact of Microstructural Units Configuration and Arrangement on Phase-Matching in Nonlinear Optical KGa5Se8 Crystals

Achieving phase-matching (PM) behavior, which is typically derived from sufficient birefringence (Δn), is crucial for maximizing the nonlinear optics (NLO) laser power output. Δn is largely attributed to the configuration and arrangement of microstructural units, and phase transitions will significantly alter the stacking method of structural units. In this study, we successfully synthesized two diamond-like isomers of α-KGa5Se8 (P21, 1) and β-KGa5Se8 (P1, 2), which consist of open-honeycomb-like anionic frameworks interspersed with embedded K+ cations. Importantly, our analysis of frequency doubling experiment data revealed a significant finding at a laser wavelength of 1910 nm: the α-phase lacks PM capability, whereas the β-phase exhibits PM behavior. Notably, through structural and computational analysis, the distinct Δn primarily stems from the different arrangements of tetrahedral units within the two phases. Specifically, the polarizability anisotropy of the tetrahedral units in β-KGa5Se8 is 3.7 times that of α-KGa5Se8. This uniform packing improves the Δn index from 0.015 (α-phase) to 0.023 (β-phase). Furthermore, β-KGa5Se8 not only demonstrates a robust PM second-harmonic generation (SHG) response (2.1 × AgGaS2 @1910 nm) but also possesses a wide band gap of 2.56 eV, surpassing the 2.33 eV threshold that corresponds to the energy of doubly frequency light using the 1064 nm laser, a characteristic often not exceeding in most selenides. This work underscores the importance of the configuration and arrangement of microstructural units for achieving PM in NLO materials.

First-Principles Path Integral Monte Carlo Studies of the Pseudo Jahn-Teller Effect in the Aromatic Cyclo[10]carbon

There has been renewed interest in carbon nanoscale structures. Experimental measurements at 4.7 K and subsequent first-principles-based vibrational diffusion Monte Carlo simulations at 0 K recently showed that the aromatic cyclo[10]carbon prefers a D5h pentagon-like structure to a regular D10h decagon. This symmetry breaking is due to the second-order Jahn-Teller effect (JTE) and has been amply described in the literature for the cumulenic cyclo[4m + 2]carbon clusters. Yet temperature dependence of the JTE in cyclo[4m + 2]carbon clusters in general and the cyclo[10]carbon in particular has not been studied systematically. In this work, we employ path integral Monte Carlo simulations on a first-principles-derived permutationally invariant potential energy surface (PES) to examine the JTE in cyclo[10]carbon as a function of temperature. The PES was trained on a set of τHCTH/cc-pVQZ energies sampled up to ∼7.7 eV above the D5h global minimum and locally adjusted to a high-level benchmark (reported by others) of the 812 cm-1 electronic energy difference between the D5h global minimum and the D10h transition state. The calculations show a strong JTE at lower temperatures with a dominant D5h composition at 100 K and a gradually diminishing JTE at higher temperatures with a washed-out pentagonal structure above 300 K.

Linear-Scaling Local Natural Orbital-Based Full Triples Treatment in Coupled-Cluster Theory

We present an efficient, asymptotically linear-scaling implementation of the canonically O ( N 8 ) coupled-cluster method with singles, doubles, and full triples excitations (CCSDT) method. We apply the domain-based local pair natural orbital (DLPNO) approach for computing CCSDT amplitudes. Our method, called DLPNO-CCSDT, uses the converged coupled-cluster amplitudes from a preceding DLPNO-CCSD(T) computation as a starting point for the solution of the CCSDT equations in the local natural orbital basis. To simplify the working equations, we t1-dress our two-electron integrals and Fock matrices, allowing our equations to take on the form of CCDT. With appropriate parameters, our method can recover more than 99.99% of the total canonical CCSDT correlation energy. In addition, we demonstrate that our method consistently yields sub-kJ mol-1 errors in relative energies when compared to canonical CCSDT, and, likewise, when computing the difference between CCSDT and CCSD(T). Finally, to highlight the low scaling of our algorithm, we present timings on linear alkanes (up to 30 carbons and 730 basis functions) and water clusters (up to 131 water molecules and 3144 basis functions).

Photophysics of 5,6,7,8-tetrahydrobiopterin on a femtosecond time-scale

Pterins are naturally occurring compounds widespread in living organisms. 5,6,7,8-Tetrahydrobiopterin (H4Bip) is a cofactor of several key enzymes, including NO-synthases and phenylalanine hydroxylase, whereas tetrahydrocyanopterin is a photoreceptor molecule in cyanobacteria. In this regard, tetrahydropterins (H4pterins) photochemistry and photophysics have been attracting our attention. H4pterins photodegrade in presence of molecular oxygen yielding dihydropterins (H2pterins) and oxidized pterins. Meanwhile, the excited states dynamics of H4pterins on a femto- and picosecond time-scale remains unclear. To shed light on this area, we perform time-resolved spectroscopy of H4Bip using fluorescence up-conversion as well as transient absorption spectroscopy techniques along with TD-DFT non-adiabatic molecular dynamics. We show that the lowest H4Bip exited state has a lifetime of ca. 200 fs. Using the BHandHLYP functional and multireference spin-flip (MRSF) method we demonstrate that starting from the S4 state, H4Bip passes to the S1 state within 50 fs, and after 200 fs a conical intersection with the ground S0 state is achieved. As a whole, the excited state behavior of H4Bip is similar to DNA nucleobases, in particular guanine. These findings allow us to make some speculations about the biochemical role of H4pterins photophysics.

Engineering Electron Lifetime for High-Performance Heterostructured 1D CdS Photocatalyst

The development of high-performance photocatalysts is essential for advancing sustainable hydrogen production. In the present work, an innovative approach to electron lifetime engineering aimed at enhancing the photocatalytic performance of 1D CdS nanowires by strategically incorporating Ni and titanium nitride (TiN) layers. It demonstrates the electron lifetime mechanism of 1D photocatalyst can be optimized through the introduction of uneven surface and heterojunction. The lifetime of electrons is influenced by the interplay between geometry and electronic structure, directly correlating with photocatalytic efficiency in an exponential decay pattern. Time-correlated single photon counting (TCSPC) measurements provide detailed insights into recombination events and non-radiative properties. Transmission electron microscopy (TEM) and ultraviolet photoemission spectroscopy (UPS) analyses reveal that the prolonged electron lifetime in CdS/Ni/TiN photocatalysts is attributed to the combination of the uneven surface and the passivation of surface energy state on CdS. The single-molecule surface catalytic sites are also observed from super-resolution fluorescence imaging. This perspective first illustrates an integrated discussion on hydrogen production, optical properties, electronic structure, and surface-active sites. The optimal heterostructured CdS achieves a 20.55-fold improvement in hydrogen production. Electron lifetime engineering offers a promising pathway in high-performance 1D photocatalysts for hydrogen production and other energy conversion applications.

Exploring Nuclear Spin Conservation in the CH2 + H2 Reaction

Nuclear spin angular momentum in molecules with identical nuclei is conserved in many physical and chemical processes, but its role in chemical reactions involving atomic rearrangements remains underexplored. In this study, we investigate the nuclear spin selection rules in the reaction between methylene (CH2) and hydrogen (H2) using high-resolution infrared spectroscopy in quantum solid parahydrogen. Our results show that in the triplet methylene (3CH2) reaction, the nuclear spin distribution of the products matches perfectly with the expected nuclear spin selection rules for the stepwise reaction mechanism. In contrast, in the excited singlet methylene (1CH2) reaction, the nuclear spin states of the methane product deviate from those predicted with a simple direct insertion mechanism. This deviation likely results from hydrogen atom dissociation due to the excess energy of the excited methane product or from a competitive process between relaxation to triplet methylene and stabilization of the methane product. Notably, our findings confirm that nuclear spin conservation is maintained even in reactions involving intermediates with unpaired electron spins such as methylene. This demonstrates the importance of detecting nuclear spin states as a powerful tool for revealing the details of reaction mechanisms, particularly in processes related to hydrocarbon combustion and planetary atmospheric chemistry.

Inter- and Intra-Molecular Charge Redistributions in H-Bonded Cyanuric Acid*Melamine (CA*M) Networks: Insight From Core Level Spectroscopy and Natural Bond Orbital Analysis

In this work, we elucidate the electronic charge redistributions that occur within the cyanuric acid (CA) and melamine (M) molecules upon formation of the triple H-bond between the imide group of CA and the diaminopyridine group of M. To achieve this, we investigated 2D H-bonded assemblies of M, CA and CA*M grown on the Au(111) surface, using X-ray photoemission (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopies. Compared to the homomolecular networks, the spectra of the mixed sample reveal core level shifts in opposite directions for CA and M, indicating a nearly complementary charge accumulation on the CA molecule and a charge depletion on the M molecule. These findings were further confirmed by theoretical simulation of the ionization potentials (IPs), which were computed using unsupported models of the H-bonded networks. A natural bond orbital (NBO) analysis performed on the three systems helped to rationalize the net charge transfer form M to CA. Finally, we observed that intramolecular interactions (electron delocalization effects) contribute progressively to the charge redistributions inside the two molecules when going from the homomolecular to the heteromolecular networks.

Global Simulations of Phase State and Equilibration Time Scales of Secondary Organic Aerosols with GEOS-Chem

The phase state of secondary organic aerosols (SOA) can range from liquid through amorphous semisolid to glassy solid, which is important to consider as it influences various multiphase processes including SOA formation and partitioning, multiphase chemistry, and cloud activation. In this study, we simulate the glass transition temperature and viscosity of SOA over the globe using the global chemical transport model, GEOS-Chem. The simulated spatial distributions show that SOA at the surface exist as liquid over equatorial regions and oceans, semisolid in the midlatitude continental regions, and glassy solid over lands with low relative humidity. The predicted SOA viscosities are mostly consistent with the available measurements. In the free troposphere, SOA particles are mostly predicted to be semisolid at 850 hPa and glassy solid at 500 hPa, except over tropical regions including Amazonia, where SOA are predicted to be low viscous. Phase state also exhibits seasonal variation with a higher frequency of semisolid and solid particles in winter compared to warmer seasons. We calculate equilibration time scales of SOA partitioning (τeq) and effective mass accommodation coefficient (αeff), indicating that τeq is shorter than the chemical time step of GEOS-Chem of 20 min and αeff is close to unity for most locations at the surface level, supporting the application of equilibrium SOA partitioning. However, τeq is prolonged and αeff is lowered over drylands and most regions in the upper troposphere, suggesting that kinetically limited growth would need to be considered for these regions in future large-scale model studies.