Applications of metal nanoclusters supported on the two-dimensional material graphene in electrocatalytic carbon dioxide reduction.

Metal nanoclusters (MNCs) have been demonstrated to exhibit superior catalytic performance compared to single nanoparticles. This is attributed to their quantized electronic structure, unique geometrical stacking and abundant active sites. While the exposed metal atoms can markedly enhance the efficiency of catalysis, unfortunately, MNCs are susceptible to agglomeration, which impairs their catalytic activity and stability.

Efficient and Robust Ab Initio Self-Consistent Field Acceleration Algorithm Based on a Semiempirical Model Hamiltonian.

A novel doubly iterative self-consistent field (SCF) approach using a semiempirical model Hamiltonian (denoted as the SMH algorithm) is proposed to accelerate the Hartree-Fock (HF) and density functional theory (DFT) calculations. This method first constructs the Fock matrix exactly in each SCF macroiteration, followed by a few SCF microiterations, where the Fock matrix is incrementally updated using an inexpensive semiempirical approximation. This leads to an improved wave function in each SCF macroiteration with minimal additional cost, and therefore a reduced number of exact Fock builds is required for SCF convergence.

Theoretical Design and Study of a Single-Atom Catalyst in Lithium-Sulfur Batteries: Edge-Type FeN Active Site Electron Density Redistribution Driven by Heteroatoms.

Lithium-sulfur (Li-S) batteries are considered to be the most promising next-generation high energy density storage systems. However, they still face challenges, such as the shuttle effect of lithium polysulfides (LiPSs) and slow sulfur oxidation-reduction kinetics. In this work, heteroatom (P and S)-doped edge-type Fe single-atom catalytic materials (FeNS/P-DG) for sulfur reduction reactions (SRRs) and sulfur oxidation reactions in Li-S batteries are investigated using density functional theory calculations.

Enhancing carrier transfer properties of Na-rich anti-perovskites, NaOM with tetrahedral anion groups: an evaluation through first-principles computational analysis.

The practical application of Na-based solid-state electrolytes (SSEs) is limited by their low level of conduction. To evaluate the impact of tetrahedral anion groups on carrier migration, we designed a set of anti-perovskite SSEs theoretically based on the previously reported NaOBr, including NaO(BH), NaO(BF), and NaO(AlH). It is essential to note that the excessive radius of anionic groups inevitably leads to lattice distortion, resulting in asymmetric migration paths and a limited improvement in carrier migration rate.

GUGA-based MRCI approach with core-valence separation approximation (CVS) for the calculation of the core-excited states of molecules.

We develop and demonstrate how to use the Graphical Unitary Group Approach (GUGA)-based MRCISD with Core-Valence Separation (CVS) approximation to compute the core-excited states. First, perform a normal Self-Consistent-Field (SCF) or valence MCSCF calculation to optimize the molecular orbitals. Second, rotate the optimized target core orbitals and append to the active space, form an extended CVS active space, and perform a CVS-MCSCF calculation for core-excited states.

Spin-Adapted Externally Contracted Multireference Configuration Interaction Method Based on Selected Reference Configurations.

As one kind of approximation of the full configuration interaction solution, the selected configuration interaction (sCI) methods have been shown to be valuable for large active spaces. However, the inclusion of dynamic correlation beyond large active spaces is necessary for more quantitative results. Since the sCI wave function can provide a compact reference for multireference methods, previously, we proposed an externally contracted multireference configuration interaction method using the sCI reference reconstructed from the density matrix renormalization group wave function [ 4747-4755].

Machine-learning assisted scheduling optimization and its application in quantum chemical calculations.

Easy and effective usage of computational resources is crucial for scientific calculations, both from the perspectives of timeliness and economic efficiency. This work proposes a bi-level optimization framework to optimize the computational sequences. Machine-learning (ML) assisted static load-balancing, and different dynamic load-balancing algorithms can be integrated.

New Light on an Old Story: Breaking Kasha's Rule in Phosphorescence Mechanism of Organic Boron Compounds and Molecule Design.

In this work, the phosphorescence mechanism of (E)-3-(((4-nitrophenyl)imino)methyl)-2H-thiochroman-4-olate-BF2 compound (S-BF2) is investigated theoretically. The phosphorescence of S-BF2 has been reassigned to the second triplet state (T2) by the density matrix renormalization group (DMRG) method combined with the multi-configurational pair density functional theory (MCPDFT) to approach the limit of theoretical accuracy. The calculated radiative and non-radiative rate constants support the breakdown of Kasha's rule further.

A theoretical study of the electrochemical reduction of CO on cerium dioxide supported palladium single atoms and nanoparticles.

Pd/CeO catalysts show superior catalytic performance owing to their optimal cycling activity and stability. In this study, single-atom Pd and eight-atom Pd nanoparticle clusters were supported on the surface of CeO(110) to investigate the effect of loaded-metal size on the catalytic performance of the Pd-CeO system for CO reduction. We investigated the CO reduction reaction (CRR) that produces C products (CO, HCOOH, CHOH, and CH) on Pd/CeO and Pd/CeO by density functional theory.

iCAS: Imposed Automatic Selection and Localization of Complete Active Spaces.

It is shown that in the spirit of "from fragments to molecule" for localizing molecular orbitals [ 3643], a prechosen set of occupied/virtual valence/core atomic/fragmental orbitals can be transformed to an equivalent set of localized occupied/virtual pre-localized molecular orbitals (pre-LMO), which can then be taken as probes to select the same number of maximally matching localized occupied/virtual Hartree-Fock (HF) or restricted open-shell HF (ROHF) molecular orbitals as the initial local orbitals spanning the desired complete active space (CAS). In each cycle of the self-consistent field (SCF) calculation, the CASSCF orbitals can be localized by means of the noniterative "top-down least-change" algorithm for localizing ROHF orbitals [ 104104] such that the maximum matching between the orbitals of two adjacent iterations can readily be monitored, leading finally to converged localized CASSCF orbitals that overlap most the guess orbitals. Such an approach is to be dubbed as "imposed CASSCF" (iCASSCF or simply iCAS in short) for good reasons: (1) it has been assumed that only those electronic states that have largest projections onto the active space defined by the prechosen atomic/fragmental orbitals are to be targeted.

Optimizing two-electron repulsion integral calculations with McMurchie-Davidson method on graphic processing unit.

In this article, several optimization methods of two-electron repulsion integral calculations on a graphic processing unit (GPU) are presented. These methods are based on the investigations of the method presented by McMurchie and Davidson (MD). A new Boys function evaluation method for the GPU calculation is introduced.

Quantum Chemical Simulation of the Absorption Spectrum of Zn Chlorin Aggregates for Artificial Photosynthesis.

Zn chlorin (Znchl) is easy to synthesize and has similar optical properties to those of bacteriochlorophyll c in the nature, which is expected to be used as a light-harvesting antenna system in artificial photosynthesis. In order to further explore the optical characteristics of Znchl, various sizes of a parallel layered Znchl-aggregate model and the THF-Znchl explicit solvent monomer model were constructed in this study, and their Qy excited state properties were simulated by using time-dependent density functional theory (TDDFT) and exciton theory. For the Znchl monomer, with a combination of the explicit solvent model and the implicit solvation model based on density (SMD), the calculated Qy excitation energy agreed very well with the experimental one.

Theoretical Study of the Anisotropy Spectra of the Valine Zwitterion and Glyceraldehyde.

The electronic absorption (EA), circular dichroism (ECD), and anisotropy spectra of the l-valine zwitterion and d-glyceraldehyde are calculated by time-dependent density functional theory (TDDFT) with the M06-2X and B3LYP functionals. It is found that the absorption and ECD spectra from TDDFT/M06-2X agree well with experimental results measured from the amorphous film of l-valine. Moreover, the calculations reproduce all three major peaks observed in the experimental anisotropy spectra.

A self-consistent coulomb bath model using density fitting.

A self-consistent Coulomb bath model is presented to provide an accurate and efficient way of performing calculations for interfragment electrostatic and polarization interactions. In this method, a condensed-phase system is partitioned into molecular fragment blocks. Each fragment is embedded in the Coulomb bath due to other fragments.

BDF: A relativistic electronic structure program package.

The BDF (Beijing Density Functional) program package is in the first place a platform for theoretical and methodological developments, standing out particularly in relativistic quantum chemical methods for chemistry and physics of atoms, molecules, and periodic solids containing heavy elements. These include the whole spectrum of relativistic Hamiltonians and their combinations with density functional theory for the electronic structure of ground states as well as time-dependent and static density functional linear response theories for electronically excited states and electric/magnetic properties. However, not to be confused by its name, BDF nowadays comprises also of standard and novel wave function-based correlation methods for the ground and excited states of strongly correlated systems of electrons [e.

Analytic Energy Gradients and Hessians of Exact Two-Component Relativistic Methods: Efficient Implementation and Extensive Applications.

The algebraic exact two-component (X2C) relativistic Hamiltonian can be viewed as a matrix functional of the decoupling () and renormalization () matrices. It is precisely their responses to external perturbations that render X2C-based response theories different in form from the nonrelativistic counterparts. However, the situation is not really bad.

Unraveling the Emission Mechanism of Radical-Based Organic Light-Emitting Diodes.

Stable doublet radical molecules have recently emerged as a promising new type of emitters in organic light-emitting diodes (OLEDs), approaching 100% internal quantum efficiency. However, the detailed emission mechanism of these open-shell emitters remains elusive. Through theoretical model analysis and first-principles calculations, we unraveled the emission mechanism of a typical emitter, (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl (TTM-1Cz).

Electronic Structure of OsSi Calculated by MS-NEVPT2 with Inclusion of the Relativistic Effects.

The electronic states of OsSi are calculated by multi-state N-electron valence state second order perturbation theory (MS-NEVPT2) with all-electron basis sets. The relativistic effects are considered comprehensively that allows us to identify the XΣ ground state. The theoretical equilibrium bond length 2.

Performance of TD-DFT for Excited States of Open-Shell Transition Metal Compounds.

Time-dependent density functional theory (TD-DFT) has been very successful in accessing low-lying excited states of closed-shell systems. However, it is much less so for excited states of open-shell systems: unrestricted Kohn-Sham based TD-DFT (U-TD-DFT) often produces physically meaningless excited states due to heavy spin contaminations, whereas restricted Kohn-Sham based TD-DFT often misses those states of lower energies. A much better variant is the explicitly spin-adapted TD-DFT (X-TD-DFT) [J.

Theoretical Study of Low-Lying Ω Electronic States of PtH and PtH.

Potential energy curves of 65 and 147 low-lying Ω states of PtH and PtH are respectively constructed using the multireference configuration interaction with singles, doubles, and Davidson's cluster corrections (MRCISD+Q), and the spin-orbit coupling effects are considered through the state-interaction approach with relativistic effective core potential spin-orbit operators. Spectroscopic constants fitted from these curves are reported and are compared with the available experimental or theoretical values. With the aid of the theoretical results including transition dipole moments, some experimentally reported electronic states and spectral bands of PtH are analyzed and reassigned.

High-resolution electronic spectra of yttrium oxide (YO): The DΣ-XΣ transition.

The DΣ-XΣ electronic absorption spectrum of the astrophysically relevant yttrium oxide (YO) molecule has been recorded for the first time in the 400-440 nm region using laser induced fluorescence. YO molecules are produced by corona discharge of oxygen between the tips of two yttrium needles in a supersonic jet expansion. An unambiguous spectroscopic identification of the DΣ-XΣ transition becomes possible from a combined analysis of the moderate-resolution laser excitation spectrum and dispersed fluorescence spectrum.

Localization of open-shell molecular orbitals via least change from fragments to molecule.

Both top-down and bottom-up localization schemes are proposed for constructing localized molecular orbitals (LMOs) of open-shell systems, via least change from fragments to molecule. The success of both schemes stems from (1) the primitive fragment LMOs that are local not only in space but also in energy and (2) the "conquer step" that allows arbitrary assignment of the unpaired electrons to fragments. Moreover, integral occupations are retained, so as to facilitate subsequent treatment of electron correlation and excitation.

Theoretical Study of Low-Lying Electronic States of PtX (X = F, Cl, Br, and I) Including Spin-Orbit Coupling.

The low-lying electronic states of platinum ions (Pt(+)) and platinum monohalides (PtX; X = F, Cl, Br, and I) are calculated using the multireference configuration interaction method with relativistic effective core potentials. The spin-orbit coupling is taken into account through the perturbative state-interaction approach. For the Ω states of PtX below 35000 cm(-1), the potential energy curves and the corresponding spectroscopic constants are reported.

Relativistic configuration interaction calculation on the ground and excited states of iridium monoxide.

We present the fully relativistic multi-reference configuration interaction calculations of the ground and low-lying excited electronic states of IrO for individual spin-orbit component. The lowest-lying state is calculated for Ω = 1/2, 3/2, 5/2, and 7/2 in order to clarify the ground state of IrO. Our calculation suggests that the ground state is of Ω = 1/2, which is highly mixed with (4)Σ(-) and (2)Π states in Λ - S notation.

First order nonadiabatic coupling matrix elements between excited states: implementation and application at the TD-DFT and pp-TDA levels.

The recently proposed rigorous yet abstract theory of first order nonadiabatic coupling matrix elements (fo-NACME) between electronically excited states [Z. Li and W. Liu, J.