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We present a practical approach to treat static and dynamical correlation accurately in large multiconfigurational systems. The static correlation is taken into account by using the spin-flip approach, which is well-known for capturing static correlation accurately at low-computational expense. Unlike previous approaches to add dynamical correlation to spin-flip models which use perturbation theory or coupled-cluster theory, we explore the ability to use the on-top pair-density functional theory approaches recently developed by Gagliardi and co-workers (J. Comput. Theor. Chem., 2014, 10, 3669). External relaxations are performed in the spin-flip calculations through a restricted active space framework for which a truncation scheme for the orbitals used in the external excitation is presented. The performance of the approach is demonstrated by computing energy gaps between ground and excited states for diradicals, triradicals, and linear polyacene chains ranging from naphthalene to dodecacene. Accurate results are obtained using the new approach for these challenging open-shell molecular systems.

The past decade has seen a great increase in the application of high-throughput computation to a variety of important problems in chemistry. However, one area which has been resistant to the high-throughput approach is multireference wave function methods, in large part due to the technicalities of setting up these calculations and in particular the not always intuitive challenge of active space selection. As we look toward a future of applying high-throughput computation to all areas of chemistry, it is important to prepare these methods for large-scale automation. Here, we propose a ranked-orbital approach to select active spaces with the goal of standardizing multireference methods for high-throughput computation. This method allows for the meaningful comparison of different active space selection schemes and orbital localizations, and we demonstrate the utility of this approach across 1120 multireference calculations for the excitation energies of small molecules. Our results reveal that it is helpful to distinguish the method used to generate orbitals from the method of ranking orbitals in terms of importance for the active space. Additionally, we propose our own orbital ranking scheme that estimates the importance of an orbital for the active space through a pair-interaction framework from orbital energies and features of the Hartree-Fock exchange matrix. We call this new scheme the "approximate pair coefficient" (APC) method and we show that it performs quite well for the test systems presented.

In this paper, the LiMg0.95TM0.05N alloy (TM=Ti, V, and Cr) undergo the Korringa-Kohn-Rostoker framework and “coherent potential approximation” to examine the magnetic and electronic behaviors, based on the MACHIKANEYAMA2002v09 program. In LiMg0.95TM0.05N alloy, the N ions around TM ions form a zinc-blende structure crystal field, which causes the Ti[d], V[d], and Cr[d] orbitals to split into the lower doubly degenerate eg(dx2-y2,dz2) and higher triply degenerate t2g(dxy,dyz,dxz) states. The “electron spin polarization (P)” of TM[d] is around the Fermi energy (Ef) and exhibits the half metallic characteristic, and the ferromagnetic stability is depicted in LiMg0.95TM0.05N. Also, the computed magnetic and the Curie temperature are valuable at room temperature as promised ferromagnetic material. The obtained values are 541.05 and 453.23 K connected to LiMg0.95V0.05N and LiMg0.95Cr0.05N, respectively. For the LiMg0.95TM0.05N alloy, the exchange splitting $$ \left({\Delta }_{\mathrm{Ex}}^{\mathrm{TM}}\right) $$ is larger than the crystal field splitting $$ \left({\Delta }_{\mathrm{CR}}^{\mathrm{TM}}\right) $$ , where $$ {\Delta }_{\mathrm{Ex}}^{\mathrm{Cr}}>{\Delta }_{\mathrm{Ex}}^{\mathrm{V}}>{\Delta }_{\mathrm{Ex}}^{\mathrm{Ti}} $$ and $$ {\Delta }_{\mathrm{CR}}^{\mathrm{Cr}}>{\Delta }_{\mathrm{CR}}^{\mathrm{V}}>{\Delta }_{\mathrm{CR}}^{\mathrm{Ti}} $$ . Also, total spin moment is arranged as follows: $$ {M}_{{\mathrm{LiMg}}_{0.95}{\mathrm{Cr}}_{0.05}\mathrm{N}}^{\mathrm{Total}}>{M}_{{\mathrm{LiMg}}_{0.95}{\mathrm{V}}_{0.05}\mathrm{N}}^{\mathrm{Total}}>{M}_{{\mathrm{LiMg}}_{0.95}{\mathrm{Ti}}_{0.05}\mathrm{N}}^{\mathrm{Total}}. $$

Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four PAHs based on the biphenylene motif finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). These results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states.

Quantum chemistry has been viewed as one of the potential early applications of quantum computing. Two techniques have been proposed for electronic structure calculations: (i) the variational quantum eigensolver and (ii) the phase-estimation algorithm. In both cases, the complexity of the problem increases for basis sets where either the Hamiltonian is not sparse, or it is sparse, but many orbitals are required to accurately describe the molecule of interest. In this work, we explore the possibility of mapping the molecular problem onto a sparse Hubbard-like Hamiltonian, which allows a Green's-function-based approach to electronic structure via a hybrid quantum-classical algorithm. We illustrate the time-evolution aspect of this methodology with a simple four-site hydrogen ring.

The ab-initio method based on density functional theory was used via local density approximation (LDA) to analyze the electronic structure of helium atoms and carbon. This involves calculating physical properties of these atoms such as effective potential, electron density and radial wave functions in both the ground state and the first three excited states. Thus, taking into account the structural complexity of the system, the calculations were carried out implicitly by the finite element method via the MATLAB software in deterministic mode. At the end of the study, the results obtained are consistent and revealing. They have shown that the effective potential of the helium atom decreases with position both in its ground state and in its first three excited states, so for the carbon atom, they have shown that these two states evolve in the same way. Regarding the electron density, the results revealed that at each radius of an atomic orbital, the electron density passes through a maximum for the helium atom while for carbon, the results show a succession of two and three peaks. Finally, with regard to radial wave functions, the results showed that the 1s orbital is closer to the nucleus than the 2s, 2p and 3s orbitals for the helium atom. For the carbon atom, the results confirm the information provided by the electron density. From the results it can be concluded that the effective potential of a multielectronic atom decreases with position and that the densest orbitals are those near the nucleus.

Topological materials with robust topological surface states appear to be well-suited as electrochemical catalysts. However, few studies have been published on the development of non-noble metal topological catalysts, most likely because the topological properties tend to be attributed to the s and p orbital electrons, while transition-metal catalysis mainly involves d orbital electrons. Herein, we proposed a topological semimetallic (TSM) compound, VAl3, with a surface state consisting mainly of d orbital electrons, as an electrocatalyst for the hydrogen evolution reaction (HER). Density functional theory (DFT) calculations showed that the surface state electrons enhanced the adsorption of H atoms. Moreover, the transfer of surface state electrons between the surface and adsorbed H atoms was optimized through nickel doping. We experimentally prepared single-crystals VAl3 and V0.75Ni0.25Al3 alloys. Electrochemical analysis showed that not only did V0.75Ni0.25Al3 outperform VAl3 but also it was among the best non-noble metal topological HER electrocatalysts currently available.

Nuclear excited states with T > 0 in sd even-even N=Z nuclei have been studied by using shell model. The calculations have employed the USDB Hamiltonian in order to predict the energy levels, the reduced electric quadrupole transition probabilities and reduced magnetic dipole transition probabilities. The study also include the average number of nucleons in each sd- active orbitals. The results compared with available experimental data. The comparison showed a good agreement between theoretical and experimental energy sates for most of the states studied in this work. On the other hand there was a difference between theoretical and experimental values of transition probabilities, but it can be said that it remained within the acceptable range of the difference.

Utilizing the magnetostrictive properties of CoFe2O4, we demonstrate reversible room temperature control of the Ti electronic structure in SrTiO3–CoFe2O4 heterostructures, by inducing local and reversible strain in the SrTiO3. By means of X-ray absorption spectroscopy, we have ascertained the changes that take place in the energy levels of the Ti 3d orbitals under the influence of an external magnetic field. The observed Ti electronic state when the sample is subjected to moderately large external magnetic fields and the disappearance of the induced phase upon their removal indicates lattice distortions that are suggestive of the development of a net electric polarization., We show reversible room temperature control of the Ti band structure in SrTiO3–CoFe2O4 heterostructures exploiting CoFe2O4 magnetostriction. Changes as a function of the applied magnetic field suggest the development of a net electric polarization.

A novel Schiff base derivative, 4,4'-(propane-1,3-diylbis(azanylylidene))bis(naphthalen-1(4H)-one) (PAN), was synthesized from the reaction of 1,4-naphthoquinone with 1,3-diaminopropane. Synthesized substance was characterized by using H-1 and C-13 NMR, FT-IR, UV-Vis spectroscopies and elemental analyses. Optimized geometry, geometric parameters, molecular electrostatic potential (MEP) diagram and vibrational wavenumbers of the PAN were calculated by using Density Functional Theory (DFT) at B3LYP/6-311G(d,p) level. H-1- and C-13-NMR chemical shifts were theoretically obtained using the gauge independent atomic orbital (GIAO) method with mentioned level of theory. Furthermore electronic transitions, frontier molecular orbital energies (FMOs) such as HOMO and LUMO were also calculated by time-dependent DFT (TD-DFT) approach. Theoretically calculated spectroscopic data were found to be quite compatible with those obtained experimentally.

Unprecedented one-step C 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 C bond cleavage leading to opening of the buckybowl (π-bowl), that could provide access to carbon-rich structures with previously inaccessible topologies, is reported; highlighting the possibility to implement drastically different synthetic routes to π-bowls in contrast to conventional ones applied for polycyclic aromatic hydrocarbons. Through theoretical modeling, we evaluated the mechanistic pathways feasible for π-bowl planarization and factors that could affect such a transformation including strain and released energies. Through employment of Marcus theory, optical spectroscopy, and crystallographic analysis, we estimated the possibility of charge transfer and electron coupling between “open” corannulene and a strong electron acceptor such as 7,7,8,8-tetracyanoquinodimethane. Alternative to a one-pot solid-state corannulene “unzipping” route, we reported a nine-step solution-based approach for preparation of novel planar “open” corannulene-based derivatives in which electronic structures and photophysical profiles were estimated through the energies and isosurfaces of the frontier natural transition orbitals., An electron shuttle contributed to breaking corannulene's heart through a unique one-step reductive CC bond cleavage in the traditionally robust π-bowl. The heartbreak did not stop there as “broken analogs” were developed through a solution-phase route.

Employing the state-of-the art Density Functional Theory (DFT) Simulations, we have investigated hydrogen storage capability in zirconium doped novel 2D heterostructures, Covalent Triazine Frameworks (CTFs), specifically CTF-1, rich in nitrogen functionalities. Zirconium atom is strongly bonded to the triazine framework with a -3.61 eV binding energy, and each Zr atom was found to adsorb 7 H2 molecules reversibly with binding energy −0.38 eV per H2 on an average giving a gravimetric storage capacity of 7.1% which accomplishes the US D.o.E. targets for suitable hydrogen storage substrates. The system stability at ambient and higher temperatures as verified using ab initio Molecular Dynamics simulations as well as existence of sufficient diffusion energy barrier preventing metal-metal clustering certifies the practical viability of the system as a high capacity H2 storage device. The mechanism of interaction of Zr on 2D CTF-1 and H2 molecules on Zr+CTF-1 have been analyzed by partial density of states, charge density distribution plot and Bader Charge Analysis. Charge transfer from Zr 4d orbital to 2p orbital of triazine ring was observed, whereas bonding of H2 is through Kubas interaction which involves the charge donation from the filled σ orbitals of hydrogen molecules to the vacant metal d orbitals, and the subsequent back donation of charge from the occupied metal d orbitals to the vacant σ∗ orbital of hydrogen molecules. As the system is stable, can hold high H2 wt% (7.1%) with suitable desorption temperature (442 K at ambient), we propose that Zr doped 2D CTF-1 can act as a potential H2 storage device.

Reducing the toxic Pb component in perovskites is an important step to realize environment-friendly perovskite optoelectronic devices. Herein, the structural, electronic, and optical properties of Zn and Mn codoped CsPbBr3 have been investigated based on first-principle calculations and experimental verifications. Although the Zn dopant could reduce the optical band gap and exciton binding energy and enhance the optical absorption and defect tolerance for CsPbBr3, the maximum reduction of the toxic Pb component was just about 12.5% in the experiment because the Zn dopant enlarges the formation energy of CsPb1-xZnxBr3. For the stable CsPb1-x-yMnxZnyBr3 perovskite, the largest y and corresponding (x + y) could reach up to 25% and 83% respectively, since the Mn dopant could reduce the structural disorder. Especially when (x + y) < 50%, CsPb1-x-yMnxZnyBr3 exhibits a comparable carrier lifetime and exciton binding energy with a lower band gap to those of the CsPbBr3, since the Zn dopant supplies a charge to CsPbBr3 to counteract the variation of Pb-Br bonds induced by the Mn dopant. Meanwhile, the d orbitals of the dopant increase the optical absorption. These suggest that a 50% reduction of toxic Pb could be realized for stable CsPb1-x-yMnxZnyBr3 with negligibly deteriorated optoelectronic properties. This work provides an alternative approach to achieve a Pb-less perovskite with a high performance.

Attaching AIE-active L1 ([1,1':2',1'':4'',1'''-quaterphenyl]-2-yldiphenylphosphane) to AuCl, shortened the distances of P-C bonds to promote electron cloud overlap between Au I and L1 , affords 1 ( L1 AuCl) with aggregation-induced phosphorescence enhancement (AIPE) activity by 3 LMCT transitions. Then substituting the coplanar L2 (9-ethynylanthracene) for the Cl - in 1 providing 2 , switches the luminescence to aggregation-caused quenching (ACQ) activity. Furthermore, we restore the performance from ACQ to AIPE by metathesis reactions to transfer 2 into 1 . It is versatile synthetic strategy of reversible transformation between 1 and 2 that switches the luminescence of organogold(I) between AIPE and ACQ through balancing auxiliary ligands around the given metal.

Important recent experimental studies have allowed the isomer-selective identification of the 2-, 3-, and 4-picolyl radicals. The picolyl radicals and their valence isoelectronic P, As, Sb, and Bi congeners are investigated here. For the three observed parent radicals, the theoretical ionization potentials agree with experiment to within 0.02 eV. Two rules are proposed for predicting vertical ionization potentials (EVIE) and relative energies. The EVIE values for these radicals will be higher when large percentages of the SOMO orbitals are distributed on the atoms with greater electronegativities. The cations of these systems were also studied along with the closed-shell methylpyridines and their P, As, Sb, and Bi analogs. The energies for the cationic species will lie lower when high percentages of π natural localized molecular orbitals occur on the more electronegative atoms. The structures of the 2- and 4-isomers strongly depend upon the heteroatoms, with the C-C linkages adopting a single-double alternating bond manner when the heteroatoms become heavier. The 3-isomers adopt roughly equal C-C bond distances with small changes from N to Bi.

Ab initio molecular dynamics (MD) with hybrid density functionals and a plane wave basis is computationally expensive due to the high computational cost of exact exchange energy evaluation. Recently, we proposed a strategy to combine adaptively compressed exchange (ACE) operator formulation and a multiple time step integration scheme to reduce the computational cost significantly [J. Chem. Phys.2019,151, 151102 ]. However, it was found that the construction of the ACE operator, which has to be done at least once in every MD time step, is computationally expensive. In the present work, systematic improvements are introduced to further speed up by employing localized orbitals for the construction of the ACE operator. By this, we could achieve a computational speedup of an order of magnitude for a periodic system containing 32 water molecules. Benchmark calculations were carried out to show the accuracy and efficiency of the method in predicting the structural and dynamical properties of bulk water. To demonstrate the applicability, computationally intensive free-energy computations at the level of hybrid density functional theory were performed to investigate (a) methyl formate hydrolysis reaction in neutral aqueous media and (b) proton-transfer reaction within the active-site residues of the class C β-lactamase enzyme.

First-principles molecular dynamics simulations, which can reveal the microscopic mechanisms and the macroscopic properties of molecules and condensed systems, have become a significant driving force in the development of physics. In the past decades, the ground state electronic properties of various materials can be accurately described using the first-principles method based on the Born-Oppenheimer approximation. However, in nonadiabatic processes, such as the ultrafast excited-state dynamics where laser interacts with molecules and condensed matters, the Born-Oppenheimer approximation evolving nuclear wave function on the ground state potential energy plane is no longer valid because of the nonnegligible nonadiabatic couplings between electrons and nuclei. In order to investigate the novel physical phenomena in nonadiabatic processes, many nonadiabatic molecular dynamics methods have been proposed, for instance, full quantum dynamics and mixed quantum-classical dynamics. When the nuclear quantum effects are trivial, the mixed quantum-classical dynamics is effective, which solves the time-dependent electron Schrodinger equation and describes the motion of the nuclei in the form of Newtonian mechanics. Two methods based on the mixed quantum-classical dynamics, the fewest-switches trajectory surface-hopping method (FSSH) and Ehrenfest dynamics, have accepted much attention since they could be easily implemented and combined with real-time time-dependent density functional theory (rt-TDDFT) for high-precision calculations. The combination of quantum and classical dynamics reduces the computational cost and allows the applications for real materials. At low temperatures, the nuclear quantum effects, including quantum tunneling and zero-point vibrations, cannot be ignored. Ring-polymer molecular dynamics (RPMD) based on the imaginary-time path integral is widely used to consider the nuclear quantum effects, which describes the quantum behavior of atomic nuclei by sampling a larger number of quantum configurations and paths. By combining RPMD and mixed quantum-classical nonadiabatic dynamics, one can describe quantum motions of nuclei and the excited electrons in quantum nonadiabatic dynamics simulations. Here, we summarize the recent progress of the rt-TDDFT methods based on numerical atomic orbital basis and plane- wave basis set, as well as highly efficient RP-TDAP method combining rt-TDDFT and RPMD towards a quantum description of electronic-nuclear dynamics. Finally, we show several representative applications employing these methods, including high harmonic generation modulated by two-color light, charge density wave dynamics, photocatalytic water decomposition as well as the quantum evolution of nuclear wave packets. These applications are in good agreement with experimental measurements, which demonstrates the reliability of these methods and their advantages in the corresponding research areas. These developments and applications are in a significant step from ground state methods to full quantum simulation of the coupled motion of electrons and nuclei, providing a new perspective for understanding and predicting the quantum interactions and dynamical behavior of condensed materials in the degree of atomic spatial scales and attosecond time scales.

Complexes with two or more magnetically coupled metal ions have attracted considerable attention as catalysts of many vital processes, single-molecule magnets, or spin-crossover compounds. Elucidation of their electronic structures is essential for understanding their catalytic and magnetic properties. Here, we provide an unprecedented insight into exchange-coupling mechanisms between the magnetic centers in six prototypical bis-μ-oxo bimetallic M2O2 complexes, including two biologically relevant models of non-heme iron enzymes. Employing multiconfigurational/multireference methods and related orbital entanglement analysis, we revealed the essential and counterintuitive role of predominantly unoccupied valence metal d orbitals in their strong antiferromagnetic coupling. We found that the participation of these orbitals is twofold. First, they enhance the superexchange between the singly occupied d orbitals. Second, they become substantially occupied and thus directly magnetically active, which we perceive as a new mechanism of the exchange interaction between the magnetic transition metal centers.

2-Cyclopenten-1-one (2CP), which is a cyclic enone, has been considered an important precursor because of its versatile functionality in the synthesis of natural products and materials for biofuels. Here, we report the adiabatic ionization energy (AIE) and cationic structure of 2CP in the ionic transition between the neutral S0 and the cationic D0 states probed by high-resolution vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. From the 0-0 band position in the VUV-MATI spectrum supported by the VUV-photoionization efficiency curve, the AIE of 2CP was determined to be 9.3477 ± 0.0004 eV (75,395 ± 3 cm-1), which is in good agreement with the reference value but much more accurate. The measured MATI spectrum combined with the Franck-Condon fitting at the B3LYP/cc-pVTZ level revealed that the cationic structure of 2CP is twisted with the C1 symmetry, whereas the neutral 2CP has the CS symmetry. The results indicate that geometrical changes induced by ionization are mainly attributed to the electron removal from the highest occupied molecular orbital, which consists of nonbonding orbitals on the oxygen atom in the carbonyl group interacting with the σ orbitals in the molecular plane of 2CP. Consequently, lowering the C1 symmetry for cationic 2CP led to the promotions of the ring-bending and ring-twisting modes in the MATI spectrum, which correspond to the ring puckering and C═C twisting in the S0 state, respectively.

Using first-principles calculations, we show that the origin of the intrinsic a1g(∼3z2 - r2)-b1g(∼x2 - y2) splitting, Δint, in tetragonal transition-metal complexes and the variations of the cubic field splitting, 10Dq, with the metal-ligand distance, R, are much more subtle than commonly thought. As a main novelty, the key role played by covalent bonding with deep valence ligand levels and thus the inadequacy of too simple models often used for the present goal is stressed. Taking as a guide the isolated D4h CuF64- complex, it is proved that Δint essentially arises from bonding with deep 2s(F) orbitals despite them lying ∼23 eV below 2p(F) orbitals. This conclusion, although surprising, is also supported by results on octahedral fluoride complexes where the contribution to 10Dq splitting from bonding with 2s(F) orbitals is behind its strong R dependence, stressing that explanations based on the crystal-field approach are simply meaningless.

We explore a pragmatic way of correcting magnetic exchange coupling constants from subsystem density-functional theory (sDFT). Our previous work [ Faraday Discuss. 2020, 224, 201−226] showed that s...

In this study, solvent-assisted co-grinding method is used to form the cocrystal of 8-hydroxy quinoline-5-sulfonic acid (HQS) and 5-chloro-8-hydroxyquinoline (CHQ). In order to determine spectroscopic and electronic properties, the theoretical characterization has been carried out. Charge delocalization patterns and second-order perturbation energies of the most interacting orbitals have also been computed and predicted. Geometrical parameters are in agreement with reported values. Molecular electrostatic potential plot predicts the reactive sites and electropositive potential region is around the hydrogen atom bonded through the nitrogen atoms, negative potentials on oxygen atoms and phenyl rings. Molecular docking of the study of the HQS-CHQ molecule has been performed for the receptors, 3C52, 4IIT, 3QYD and 4FGY.

Despite being the most accurate class of density functional approximations for the main-group chemistry, doubly hybrid approximations (DHAs) are generally considered to be incomplete in describing the medium- to long-range dispersive interactions. The existing DHAs are often supplemented with empirical long-range dispersion corrections. By using the extensive and chemically diverse GMTKN55 database, we explore the limits of the XYG3-type DHAs using the B3LYP reference orbitals, namely, xDH@B3LYP, with a gradually relaxed constraint on the mixing parameters of DHAs. Our results demonstrate that the xDH@B3LYP model can provide a balanced description of both covalent and noncovalent interactions with the accuracy and robustness comparable to or even better than the very expensive composite methods in wave function theory. Such an accuracy can be achieved without resorting to the use of any long-range correction scheme, shedding new light on the development of DHAs.

Two tocotrienol derivatives, garcipaucinones A (1) and B (2), and a biosynthetically related known analogue (3) were isolated from the fruit of Garcinia paucinervis. Their structures including absolute configurations were unequivocally determined by spectroscopic methods complemented with electronic circular dichroism (ECD) calculations and gauge-independent atomic orbital (GIAO) NMR calculations. Compounds 1 and 2 are the first naturally occurring tocotrienol derivatives with a 3,10-dioxatricyclo-[7.3.1.02,7]tridecane skeleton incorporating an unusual γ-pyrone motif. A reasonable biosynthetic pathway for formation of the two compounds is proposed. The antiproliferative and anti-inflammatory activities of compounds 1 and 2 were also evaluated.

A spectroscopic approach to measuring a charge qubit placed in a waveguide consisting of three microcavities (a photonic molecule) is discussed. The logical states of a qubit are represented by the single-electron orbitals of a semiconductor double quantum dot. The impact of different factors that cause deviations of the system’s parameters from specified values ​​is investigated. The possibility of controlling the spectrum of a photonic molecule using a local change in its dielectric properties in order to optimize the qubit measurement procedure is analyzed. The functions of the measuring contrast and signal-to-noise ratio are calculated depending on the main parameters of the system.

Tuning the electronic states near the Fermi level can effectively facilitate the reaction kinetics. However, elucidating the role of a specific electronic state of metal oxide in simultaneously regulating the CO 2 electroreduction reaction (CO 2 RR) and competing hydrogen evolution reaction (HER) is still rare, making it difficult to accurately predict the practical CO 2 RR performance. Herein, replacing the Zn site by heteroatoms with different outer electrons (Mo and Cu) is found to tune both occupied and unoccupied orbitals near the Fermi level of ZnO. Moreover, the different electronic states significantly modulate both CO 2 RR and HER activity with a totally inverse trend, thus dramatically tuning the practical CO 2 RR performance. In parallel, the correlation between electronic states, reaction free energies and practical activity is demonstrated. This work provides a possibility for engineering efficient CO 2 RR eletrocatalysts through tunable composition and electronic structures.

For the large and chemically diverse GMTKN55 benchmark suite, we have studied the performance of density-corrected density functional theory (HF-DFT), compared to self-consistent DFT, for several pure and hybrid GGA and meta-GGA exchange-correlation (XC) functionals (PBE, BLYP, TPSS, SCAN) as a function of the percentage of HF exchange in the hybrid. The D4 empirical dispersion correction has been added throughout. For subsets dominated by dynamical correlation -- particularly noncovalent interaction subsets -- HF-DFT is highly beneficial, particularly at low HF exchange percentages. For subsets with significant static correlation (i.e., where a Hartree-Fock determinant is not a good zero-order wavefunction), HF-DFT may do more harm than good. While the self-consistent series show optima at or near 37.5% (i.e., 3/8) for all four XC functionals -- consistent with Grimme's proposal of the PBE38 functional -- HF-BnLYP-D4, HF-PBEn-D4, and HF-TPSSn-D4 all exhibit minima nearer 25% (i.e., 1/4). Intriguingly, for HF-SCANn-D4, the minimum is near 10%, but the weighted mean absolute error (WTMAD2) for GMTKN55 is only barely lower than that of HF-SCAN-D4 (i.e., where the post-HF step is a pure meta-GGA). The latter becomes an attractive option, only slightly more costly than pure Hartree-Fock, and devoid of adjustable parameters other than the three in the dispersion correction. Moreover, its WTMAD2 is only surpassed by the highly empirical M06-2X and by the combinatorically optimized empirical range-separated hybrids wB97X-V and wB97M-V., Comment: Journal of Chemical Theory and Computation (2021)

Mechanistic understanding on the electronic structure of α'-Ga2S3 unravel that the electrons in nonbonding 3pz orbitals of two-coordinated S2- anions are photoexcited to the adjacent σ-type antibonding orbitals (Ga-4s and S-3p) and migrate thereafter to the surface along the a-axis. By introduction of the In-S antibonding on the one hand and modifying the local dipole moment on the other hand, the light absorption ability and charge separation efficiency can be both enhanced by In3+-to-Ga3+ substitution, and the photocatalytic H2 evolution rate can be significantly promoted. Local geometric distortion is common in solid solutions, but its effect on charge migration behavior has yet been considered in semiconducting photocatalysis. Our case study on In3+-doped Ga2S3 is a good reminder of such the importance.

More research work has focused on device structure preparation, doping modification, and interface control of CsPbI2Br-based solar cells, whereas less basic theoretical research has been carried out on CsPbI2Br-based perovskite solar cells. It is necessary to find a suitable method to accurately describe the microscopic properties of CsPbI2Br-based perovskite solar cells. Therefore, this paper starts from the interface regulation of all-inorganic perovskite CsPbI2Br to study in detail the local lattice and electronic properties of the light-absorbing layer (CsPbI2Br)/electron transporting layer (SnO2) heterogeneous interface at the atomic and electronic levels by using first-principles calculations based on density functional theory (DFT). The results show that the lattice mismatch at the CsPbI2Br (100)/SnO2 (110) heterogeneous interface is 6.4% while the interface binding energy is −0.79 J/m2, indicating that the interface orientation and bonding modes can exist stably. Density of states (DOS) calculations reveal that the CsPbI2Br (100)/SnO2 (110) interface presents some interface states caused by I 5p and O 2p orbitals near to the Fermi level, which is one of the reasons for the low conversion efficiency of such solar cells.

A-sites join the band edge The band edge of hybrid organic-inorganic perovskites, which have the general formula ABX 3 , is mainly controlled by the inorganic X anions (such as chloride) and the B cation (such as lead). Organic A-site cations usually only exert indirect structural effects because their electronic levels lie far from the band edge. Xue et al. show that cations with large π-conjugated structures can interact with inorganic frontier molecular orbitals. A surface layer of ethylammonium pyrene, which had an optimal intercalation distance, increased hole mobilities and power conversion efficiencies relative to a reference inorganic perovskite and also improved device stability. Science , this issue p. 636

NH2-UIO66 (NU) is a promising photocatalyst for the reduction of Cr(VI) to low-toxic Cr(III) driven by visible light under ambient conditions. However, the main limitation in this process is the inefficient ligand to metal charge transfer (LMCT) of photo-excited electrons, which is caused by inherent energy gap (ΔELMCT). This study synthesized the defective NU (NUX-H, where X is the molar equivalent of the modulator) with reduced ΔELMCTthrough linkers removal via acid treatment. The electronic structure of NUX-H was systematically investigated, and the results indicated that the structural defects in NUX-H strongly altered the environment of the Zr atoms. Furthermore, they substantially lowered the energy of the unoccupied d orbitals (LUMO), which was beneficial to efficient LMCT, resulting in an improved photocatalytic activity of NUX-H toward high-concentration (100 mg/L) Cr(VI) reduction. Compared to NU with defect-free structure, the reducing rate of Cr(VI) was increased by 47 times. This work introduced an alternative strategy in terms of designing efficient photocatalysts for reducing Cr(VI) under ambient conditions.

Clusters (Ih)-(Cd, Hg, Yb)@(Pb12, Sn12), (C5v)-(Ag, Au)@BiPb11, (C5v)-Ag@SbSn11, (D5d)(Ni, Pd, Pt)@Bi2Pb10, (D5d)-Pd@Sb2Sn10, (C3v)-(Pb12, Sn12)·(Pb, Sr, Ba), closo-Bi2Pb10, closo-Bi2Pb4, closo-Sb2Sn4, (Ih)-Bi20, (Ih)-Kr@Bi20, and (Ih)-Ni12Bi20 were studied by the DFT PBE0 method. Structures of (Ih)-(Pb, Sr)@(Pb12, Sn12), (Ih)-Ba@Pb12, (D5d)-(He, Ne)@Bi2Pb10, (C3v)-(Pb12, Sn12)∙Yb, (C5v)-(Pb12, Sn12)∙Hg, (Cs)-BiPb11∙(Ag, Au), (Cs)-SbSn11∙Ag, (Cs)-p-Bi2Pb10∙(Ni, Pd, Pt), and (Cs)-p-Sb2Sn10∙Pd clusters are metastable; structures of (Ih)-Ba@Sn12 and (D5d)-(Ar, Kr, Rn)@Bi2Pb10 are unstable. In the (Ih)-Ni12Bi20 cluster, nickel atoms form η5-bonds with the faces of the Bi20 dodecahedron. In the isomers (D4h)- and (C2v)-(Bi, Sb)2(Pb, Sn)4, 6 orbitals of lone electron pairs and 8 bonding three-center orbitals with populations of 2.00 make up a linearly dependent set of 14 natural orbitals. The oxidation state ΞX is associated with the populations of orthogonal orbitals located outside the X atom.

In the linear‐scaling divide‐and‐conquer (DC) electronic structure method, each subsystem is calculated together with the neighboring buffer region, the size of which affects the energy error introduced by the fragmentation in the DC method. The DC self‐consistent field calculation utilizes a scheme to automatically determine the appropriate buffer region that is as compact as possible for reducing the computational time while maintaining acceptable accuracy (J. Comput. Chem. 2018, 39, 909). To extend the automatic determination scheme of the buffer region to the DC second‐order Møller–Plesset perturbation (MP2) calculation, a scheme for estimating the subsystem MP2 correlation energy contribution from each atom in the buffer region is proposed. The estimation is based on the atomic orbital Laplace MP2 formalism. Based on this, an automatic buffer determination scheme for the DC‐MP2 calculation is constructed and its performance for several types of systems is assessed., In the linear‐scaling divide‐and‐conquer (DC) electronic structure method, each subsystem is calculated together with the neighboring buffer region, the size of which affects the energy error introduced by the fragmentation. The authors have proposed a scheme to automatically determine the appropriate buffer region for DC Hartree–Fock (HF) calculation that is as compact as possible for reducing the computational time while maintaining acceptable accuracy. They extend the automatic buffer determination scheme to DC second‐order Møller–Plesset perturbation (MP2) calculation. In this scheme, the buffer atoms for DC‐MP2 calculation are selected from those for DC‐HF based on the estimated correlation energy contribution.

The theoretical calculations on triplet linear and non-linear structures of nitrosyl halides XNO (X = Cl, Br, and I) confirm that the origin of instability and symmetry breaking of XNO linear structures is a pseudo-Jahn–Teller effect (PJTE). However, the PJTE associated with electron delocalization may prove the stability of XNO non-linear structures best. The distortion of high-symmetry (C∞v) configurations in XNOs emerges from mixing the PJT with ground 3Σ– and the excited 3Π states in the Qπ direction, which consequently make the ground state unstable. The PJT problem is formulated in the form (3Σ– + 3Π) $$ \otimes $$ π. The energy difference between high-symmetry C∞v geometries and low-symmetry Cs geometries energy gap between the ground and excited states decreases from ClNO to INO. Also, ΔEPJT (i.e., the difference of energy between the highest occupied molecular orbital (HOMO; LPX), and the lowest unoccupied molecular orbital (LUMO; $$\pi _{{{\text{NO}}}}^{*}$$ )) plays an important role in the instability of structures. Electron delocalization decreases and PJT instability increases from ClNO to INO in high-symmetry C∞v geometries. According to the results of the canonical molecular orbital (CMO) analysis, the contribution of the LPX non-bonding orbitals in the vibronic coupling constant (F) increases from ClNO to INO. Also, the NBODEL results indicate that the instability of compounds increases from ClNO to INO. Because the primary force constant is positive, the curvature of ground electronic state configuration curves in adiabatic potential energy surfaces (APESs) decreases from ClNO to INO. The variations of the chemical hardness differences between the non-linear (Cs) and linear (C∞v) structures decrease from ClNO to INO and of chemical potential differences increase from ClNO to INO, justifying the variation trend of ΔEPJT. Furthermore, based on the obtained results, Δ[η(Cs) – η(C∞v)] obeys the maximum hardness principle.

Hartree Fock (HF) and Density Functional Theory (DFT) have been commonly used to model chemical problems. This study uses the Molecular Orbital Theory (MOT) to evaluate the electronic structure of five diatomic molecules generated by HF and DFT calculations. The evaluation provides an explanation of how the orbitals of a molecule come to be and how this affects the calculation of the physical quantities of the molecule. The evaluation is obtained after comparing the orbital wave functions calculated by MOT, HF, and DFT. This study found that the nature of the Highest Occupied Molecular Orbital (HOMO) of a molecule is determined by the valence orbital properties of the constituent atoms. This HOMO property greatly influences the precision of calculating the molecular electric dipole moment. This shows the importance of understanding the orbital properties of a molecule formed from the HF and DFT calculations

We investigatethe electronic and structural properties of two new amorphous materials, Bi6Ca2O28B12 and Bi6Ca2 O28B11:Tm, using density functional theory with a short-range description similar to that for crystalline solids and by considering the Tm 4f states as core states. Our results show that the valence band is formed by broadband states with a strong presence of the O − 2p orbital states in both materials. The thulium-doped structure shows an increased band gap, indicating the strong presence of this rare earth in connection with the oxygen. Both materials exhibit a narrow band gap. Calculations related to the electronic transition of the orbitals between the highest occupied valence band and the lowest unoccupied conduction band and the density charge show a significant contribution of bismuth and oxygen in the formation of both materials. Our results present important information that can assist in the investigation of the technological applications of devices with a design focus for solid-state lasers.

As quantum computing approaches its first commercial implementations, quantum simulation emerges as a potentially ground-breaking technology for several domains, including Biology and Chemistry. However, taking advantage of quantum algorithms in Quantum Chemistry raises a number of theoretical and practical challenges at different levels, from the conception to its actual execution. We go through such challenges in a case study of a quantum simulation for the hydrogen (H2) and lithium hydride (LiH) molecules, at an actual commercially available quantum computer, the IBM Q. The former molecule has always been a playground for testing approximate calculation methods in Quantum Chemistry, while the latter is just a little bit more complex, lacking the mirror symmetry of the former. Using the Variational Quantum Eigensolver (VQE) method, we study the molecule's ground state energy versus interatomic distance, under the action of stationary electric fields (Stark effect). Additionally, we review the necessary calculations of the matrix elements of the second quantization Hamiltonian encompassing the extra terms concerning the action of electric fields, using STO-LG type atomic orbitals to build the minimal basis sets.

The many-body expansion (MBE) of energies of molecular clusters or solids offers a way to detect and analyze errors of theoretical methods that could go unnoticed if only the total energy of the system was considered. In this regard, the interaction between the methane molecule and its enclosing dodecahedral water cage, CH$_4$(H$_2$O)$_{20}$, is a stringent test for approximate methods, including density-functional theory (DFT) approximations. Hybrid and semilocal DFT approximations behave erratically for this system, with three- and four-body nonadditive terms having neither the correct sign nor magnitude. Here we analyze to what extent these qualitative errors in different MBE contributions are conveyed to post-Kohn-Sham random-phase approximation (RPA). The results reveal a correlation between the quality of the DFT input states and the RPA results. Moreover, the renormalized singles energy (RSE) corrections play a crucial role in all orders of MBE. For dimers, RSE corrects the RPA underbinding for every tested Kohn-Sham model: generalized-gradient approximation (GGA), meta-GGA, (meta-)GGA hybrids, as well as the optimized effective potential at the correlated level. Remarkably, the inclusion of singles in RPA can also correct the wrong signs of three- and four-body nonadditive energies as well as mitigate the excessive higher-order contributions to the MBE. The RPA errors are dominated by the contributions of compact clusters. As a workable method for large systems, we propose to replace those compact contributions with CCSD(T) energies and to sum up the remaining many-body contributions up to infinity with supermolecular or periodic RPA. As a demonstration of this approach, we show that for RPA(PBE0)+RSE it suffices to apply CCSD(T) to dimers and 30 compact, hydrogen-bonded trimers to get the methane-water cage interaction energy to within 1.6% of the reference value., Comment: Data available at https://doi.org/10.5281/zenodo.4429677

The ground and low-lying excited state electronic structural properties (such as equilibrium geometries, harmonic frequencies, excitation energies, barrier energy, and so on) of the methylene amidogene radical (H

The electron paramagnetic resonance (EPR) parameters and local structures for Cu 2+ in (100-2x)TeO 2 -xAg 2 O-xWO 3 (TAW) (7.5 ≤ x ≤ 30 mol %) glasses are quantitatively studied for distinct modifier concentrations x. The octahedral Cu 2+ centers are subject to the medium tetragonal elongations of about 2% along the C 4 axis due to the Jahn-Teller effect. By utilizing only three adjusted coefficients a , b and ω , the quantities ( Dq , k , t and κ) can be suitably characterized by the Fourier type functions, which reasonably account for the experimental concentration dependences of the d-d transition bands and EPR parameters. The calculation results are discussed, and the mechanisms of the above concentration dependences of these quantities are illustrated by the modifications of the local structures and the electron cloud distribution around the Cu 2+ dopant with the variations of the concentration x.

While CCSD(T) with spin-restricted Hartree-Fock (RHF) orbitals has long been lauded for its ability to accurately describe closed-shell interactions, the performance of CCSD(T) on open-shell species is much more erratic, especially when using a spin-unrestricted HF (UHF) reference. Previous studies have shown improved treatment of open-shell systems when a non-HF set of molecular orbitals, like Brueckner or Kohn-Sham density functional theory (DFT) orbitals, is used as a reference. Inspired by the success of regularized orbital-optimized second-order Møller-Plesset perturbation theory (κ-OOMP2) orbitals as reference orbitals for MP3, we investigate the use of κ-OOMP2 orbitals and various DFT orbitals as reference orbitals for CCSD(T) calculations of the corrected ground-state harmonic vibrational frequencies of a set of 36 closed-shell (29 neutrals, 6 cations, 1 anion) and 59 open-shell diatomic species (38 neutrals, 15 cations, 6 anions). The aug-cc-pwCVTZ basis set is used for all calculations. The use of κ-OOMP2 orbitals in this context alleviates difficult cases observed for both UHF orbitals and OOMP2 orbitals. Removing two multireference systems and 12 systems with ambiguous experimental data leaves a pruned data set. Overall performance on the pruned data set highlights CCSD(T) with a B97 orbital reference (CCSD(T):B97), CCSD(T) with a κ-OOMP2 orbital reference (CCSD(T):κ-OOMP2), and CCSD(T) with a B97M-rV orbital reference (CCSD(T):B97M-rV) with RMSDs of 8.48 cm-1, and 8.50 cm-1, and 8.75 cm-1 respectively, outperforming CCSD(T):UHF by nearly a factor of 5. Moreover, the performance on the closed- and open-shell subsets shows these methods are able to treat open-shell and closed-shell systems with comparable accuracy and robustness. CCSD(T) with RHF orbitals is seen to improve upon UHF for the closed-shell species, while spatial symmetry breaking in a number of restricted open-shell HF (ROHF) references leads CCSD(T) with ROHF reference orbitals to exhibit the poorest statistical performance of all methods surveyed for open-shell species. The use of κ-OOMP2 orbitals has also proven useful in diagnosing multireference character that can hinder the reliability of CCSD(T).

Two-dimensional porous organic polymers (POPs) can offer overlapped π electron clouds between the stacked layers, conjugated skeletons, and multiple high-rate charge carriers transport pathways tha...

Here, we report experimental evidence of interparticle spatial overlapping of orbitals to result in interparticle charge-transfer excitation (ICTE) at an anatase-rutile interface which is expected to be applicable to clarify the relative band position of metal-oxides and mixture homogeneity of mixture samples measured by reversed double-beam photoacoustic spectroscopy.

A first-principles investigation is carried out on palladium (Pd)-doped armchair graphene nanoribbons (AGNRs) to investigate their structural, electronic and transport properties. The structural analysis of the considered Pd-doped nanoribbons reveals that single Pd doping at the edges of AGNRs results in the most stable configuration. The present findings reveal that the electronic transport properties are strongly dependent on the number of dopant atoms and their positions. Furthermore, it is noted that the proposed two-probe devices exhibit peculiar nonlinear I–V characteristics indicating potential for rectification behavior. Excellent high rectification ratio (RR) and reverse rectification ratio (RRR) are on the order of $$1.8\times 10^{5}$$ and $$9.7\times 10^{4}$$ , respectively, are found for center-Pd-doped 7-AGNRs. The interesting rectifying I–V behavior can be explained by the localization/delocalization effect of frontier orbitals along with the variation of the transmission spectra with the applied bias voltage. These findings indicate that Pd-doped armchair GNRs are a potential candidate for use in next-generation ultralow-power nanoscale switching devices.

Relativistic effects are quite large for the actinide 5f and 6d open shells, and in the present study we present combinatorial enumeration of $$\upomega {{-}} \upomega $$ states of all 14 actinide (lanthanide) dimers using multinomial symmetric function (S-function) techniques. The techniques presented here enumerate all possible $$\upomega {{-}} \upomega $$ states that arise from relativistic 2-component molecular spinors composed of the 7s, 6d 5f, and possibly 7p shells of the actinide dimers Th2 through Lr2. The combinatorial enumerations techniques reveal that that for Americium dimer (Am2) there are 20,058,300 S-function terms of which only 616,227 terms satisfy the Pauli exclusion principle yielding 401,166,110 $$\upomega {{-}} \upomega $$ states (142.6 MB of output), all of which arise from primarily the 7s/6d/5f shells of Am. Explicit tables are constructed for the relativistic $$\upomega {{-}} \upomega $$ states for Th2 to Am2 with several restrictions imposed on the levels of excitations primarily to reduce the table sizes, and through the electron–hole equivalence $$\upomega {{-}} \upomega $$ states of the remaining dimers of the actinide row are enumerated. The computational and mathematical techniques also enumerate the $$\upomega {{-}} \upomega $$ states of Ce2 to Eu2 and by electron–hole equivalence Gd2 to Tm2, although spin–orbit splittings are smaller for lanthanides. A unique feature of the present combinatorial technique is that it facilitates any number of orbitals and any number of open shells including the possibility of 14 singly-occupied orbitals for actinide and lanthanide dimers, and thus providing for a technique to enumerate $$\upomega {{-}} \upomega $$ states arising from both very high spin open-shell states as well as low spin states exhaustively.