AB INITIO STUDY ON THE REACTION OF CH WITH NH3

The mechanism of the reaction of the CH radical with NH3 has been theoretically studied at the MP2/6-31G** level. The calculation results Indicate that the insertion reaction path Is the favourable channel, which is in line with Lin's proposal based on their kinetic experiments. A detailed description of the complicated insertion reaction path is presented.

Defect stability in thorium monocarbide:An ab initio study

The elastic properties and point defects of thorium monocarbide（ThC） have been studied by means of density functional theory based on the projector-augmented-wave method. The calculated electronic and elastic properties of ThC are in good agreement with experimental data and previous theoretical results. Five types of point defects have been considered in our study, including the vacancy defect, interstitial defect, antisite defect, schottky defect, and composition-conserving defect. Among these defects, the carbon vacancy defect has the lowest formation energy of 0.29 eV. The second most stable defect（0.49 eV） is one of composition-conserving defects in which one carbon is removed to another carbon site forming a C2 dimer. In addition, we also discuss several kinds of carbon interstitial defects, and predict that the carbon trimer configuration may be a transition state for a carbon dimer diffusion in Th C.

AB INITIO STUDY OF LOW-LYING ELECTRONIC STATES OF THE AsH_2 RADICAL

The equilibrium geometries,excitation energies,force constants and vibrational frequencies for the low-ly- ing electronic states X ~2B_1,~2A_1,~2B_2 and ~2A_2 of the AsH_2 radical have been calculated at the MRSDCI level with a 3-21G~* basis set.Our calculated geometries,excitation enegies and vibional frequencies for the X ~2B_1 and ~2A_1 states are in good agreement with available experimental data.The electronic transition dipole mo- ments,oscillator strengths for the ~2A_1→X ~2B_1 and ~2A_2→X ~2B_1 transitions,radiative lifetimes for the ~2A_1 and ~2A_2 states are calculated based on the MRSDC^1 wavefunctions,predicting results in reasonable agreement with available experiment.

Ab Initio Study of the Dynamical Si-O Bond Breaking Event in α-Quartz

The Si-O bond breaking event in the a-quartz at the first triplet （T1） excitation state is studied by using ab initio molecular dynamics （AIMD） and nudged elastic band calculations. A meta-stable non-bridging oxygen hole center and E1 center （NBOHC-E） is observed in the AIMD which consists of a broken Si-O bond with a Si-O distance of 2.54A. By disallowing the re-bonding of the Si and 0 atoms, another defect configuration （lll- Si/V-Si） is obtained and validated to be stable at both ground and excitation states. The NBOHC-E is found to present on the minimal energy pathway of the initial to IlI-Si/V-Si transition, showing that the generating of the NBOHC-E is an important step of the excitation induced structure defect. The energy barriers to produce the NBQHC-E＇ and Ⅲ-Si/V-Si defects are calculated to be 1.19 and 1.28eV, respectively. The electronic structures of the two defects are calculated by the self-consistent GW calculations and the results show a clear electron transition from the bonding orbital to the non-bonding orbital.

Ab Initio Study on Structural and Magnetic Properties of Ni-Pd and Ni-Pt Linear and Zigzag Nanowires

Employing the accurate frozen-core full-potential projector augmented-wave method,the self-consistentelectronic structure calculations were carried out on pure Ni,Pd,Pt and mixed Ni-Pd and Ni-Pt free-standing linear andzigzag nanowires.The bond lengths for all these systems are generally increased as their structures change from the linearto the zigzag chain.The bond lengths for Ni-Pd and Ni-Pt wires are in between the values of corresponding pure systemand the bond angles around 60° suggesting the possible formation of Ni-Pd and Ni-Pt bimetallic materials.In mixedNi-Pd and Ni-Pt chains,the Ni,Pd,and Pt atoms have quite high local magnetic moments.The calculations suggestthat the magnetic moments in linear nanowires are generally larger than the ones of corresponding zigzag nanowires.Itis found that there is hybridization between Ni 3d and Pd 4d,Ni 3d and Pt 5d states,which may significantly affectstructural stability and magnetism of Ni-Pd and Ni-Pt nanowires.

Ab Initio Study of Single-and Double-Electron Capture Processes in Collisions of He^(2+) Ions and Ne Atoms

The single-and double-electron capture(SEC, DEC) processes of He^(2+) ions colliding with Ne atoms are studied by utilizing the full quantum-mechanical molecular-orbital close-coupling method. Total and state-selective SEC and DEC cross sections are presented in the energy region of 2 eV/u to 20 keV/u. Results show that the dominant reaction channel is Ne^(+)(2s2p^(6) ^(2)S) + He^(+)(1s) in the considered energy region due to strong couplings with the initial state Ne(2s^(2)2p^(6)^(1)S) + He^(2+) around the internuclear distance of 4.6 a.u. In our calculations, the SEC cross sections decrease initially and then increase whereby, the minimum point is around 0.38 keV/u with the increase of collision energies. After considering the effects of the electron translation factor(ETF), the SEC cross sections are increased by 15%–25% nearby the energy region of keV/u and agree better with the available results. The DEC cross sections are smaller than those of SEC because of the larger energy gaps and no strong couplings with the initial state. Due to the Demkov-type couplings between DEC channel Ne^(2+)(2s^(2)2p^(4)^(1)S) + He(1s^(2)) and the dominating SEC channel Ne^(+)(2s2p^(6) ^(2)S) + He^(+)(1s), the DEC cross sections increase with increasing impact energies. Good consistency can also be found between the present DEC and the experimental measurements in the overlapping energy region.

Ab Initio Study of NH_3-CH_3OH Neutral and Ionic Clusters

NH3-CH3OH system was studied by ab initio calculations at the Hartree-Fock level using the 6-31Gbasis set. Equilibrium geometries of both of its ionic (type I and II) and neutral clusters are obtained. Different dissociation channels are evaluated for I and II, respectively. The results suggest that when NH3-CH3OH is vertically ionized,CH3O + NH+ are the dominant products via a proton transfer reaction, and accompanying the dissociation of (NH3-CH3OH)+ver to NH3 + + CH3OH, intracluster charge transfer process takes place in the system.

Ab initio study of dynamical properties of U-Nb alloy melt

The U-Nb alloy,as a kind of nuclear material with good corrosion resistance and mechanical properties,plays an important role in the nuclear industry.However,the experimental measurements and theoretical calculations of many parameters which are essential in describing the dynamical properties of this alloy melt,including density,diffusivity,and viscosity,have not been carried out yet.The lack of data on the dynamical properties of nuclear materials seriously hinders the high-performance nuclear materials from being developed and applied.In this work,the dynamical properties of the U-Nb alloy melt are systematically studied by means of ab initio molecular dynamics simulations and their corresponding mathematical models are established,thereby being able to rapidly calculate the densities,diffusion coefficients,viscosities,and their activation energies in the whole U-Nb liquid region.This work provides a new idea for investigating the dynamical properties of binary alloy melts,thereby promoting the development of melt research.

AB INITIO STUDY ON GAS-PHASE FACTION OF Ca WITH HN_3

The reaction of Ca with HN3 has been investigated theoretically by an ah initio MO methodwith electron correlation being taken into account by second-order MLLER-PLESSET(MP2)perturbation theory Two possible product channels. CaN3+H. CaNH+N2, on the potential energysurfaces(PESs) have been examined and the reaction mechanism discussed. Values of tile HN-NZ,HN3, Ca-N3 and Ca-AH bond dissociation energy are also calculated, which are in good agreement withexperiment

Ab Initio Study on the Reaction of La￣+ + CH_4→La+-CH￣2 + H_2

Ab initio study on the reaction or the ground state (a3F) and excited state (a1D) or La+with methane has been Performed. performed. channel on the singlet and triplet potential energysurface (PES) has been examined and the reaction mechanism are discussed. Comparisons betweensinglet and triplet PESs show that the ex￣ state (aiD) of La+ is more r￣ than its groundstate (a3F) due tO the SPin quantum number conservation with the more stable insertion intermediate for excited state (1D), which is in good agreement with the experiment.

Relaxation of 6H-SiC(0001) Surface and Si Adsorption on 6H-SiC(0001):an ab initio Study

First-principles calculations are carried out to study the relaxation of 6H-SiC （0001） surface and chemisorption models of Si adatoms on four high-symmetry adsorption sites. The surface results show that Si-termination is the preferred termination of the 6H-SiC（0001） polar surface and is more stable than the C-terminated 61-1- SiC（0001） polar surface over a wide range of allowed chemical potentials. Four stable atomic configurations （top, bridge, hcp and fcc） are considered, and the adsorption energies and geometries, Mulliken charge population, and partial density of state （PDOS） properties are analyzed. Adsorption energy results show that the top site is the most stable site. The structural properties of Si adsorption on the SiC （0001） surface shows that increasing stability means decreasing bond lengths. Charge populations analysis and PDOS results imply that there is strong interaction between Si adatoms and 6H-SiC （0001） surface.

AB INITIO STUDY OF 1,2-DITHIOSQUARIC ACID

Result of ab initio SCF calculation of 1,2-dithiosquaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dithione) are reported. The ZZ isomer is found to be the most stable of the three isomers. An isodesmic energy analysis has been carried out at the HF 6-31G*//6-31G* level for the three planar isomers. The three isomers have positive isodesmic energies or small negative ones, suggesting that 1,2-dithiosquaric acid is not aromatic. Vibrational frequencies have also been calculated for the three isomers.

Ab initio Study on the Interaction of La (Ⅲ) with Adrenaline

The interaction of La(III) with adrenaline was studied using Ab initio mathod. The geometry of the complex of La (III) with adrenaline was optimized, and the La(III) bonding site in adrenaline was ascertained

Ab Initio Study of the Oxygen Atom Abstracting Hydrogen from Difluoromethane and Dichloromethane

The three potential surfaces for reactions of the O atom to abstract H atoms from CH2F2 and CH2Cl2 were studied using the ab initio method. The frequencies, geometries and energies of all species are calculated. The best estimates of the heat of reactions are 30.92 KJ/mol and 13.01 KJ/mol, and, the best potential barrier heights for both reactions are calculated to be 74.50 KJ/mol and 67.22 KJ/mol, respectively. the second-order rate coefficients calculated are 2.8721x10(-21) and 4.2522x10(-20) cm(3)/molecule-s at 298 K, respectively.

From atom to monatomic wire:an ab initio study of magnetism in 3d transition metals

A systematic ab initio study on magnetism of the 3d transition metals（TM） from atom to monoatomic wire within density functional theory with generalized gradient approximation（GGA） was performed.The results show that the spin coupling has strong intraatomic exchange strengths about 1 eV for isolated 3d TM atoms.The magnetic moments are distinctly lower than those of free atoms for all dimers except Mn 2 .All the 3d TM elements exhibit magnetic ground states in the linear wire structure.

Ab initio study on structures and stabilities of OLi_n hyperlithiated compounds

Thc grometries of hyperlithiated compounds OLi n were optimized by means of HF, MP2 and DFT methods with 6-31G· basis set. Thc dissociation energies of those optimized stable geometries of OLi n were calculated, the results are in good agreement with experimental values; and moreover, the dissociation energy of OLi6 is predicted. In addition, the fundamental vibrational frequencies were also predicted.

Ab initio study of vibrational frequencies, force field and normal coordinate analysis of the cis- and trans-isomers of nitrosomethanol

In this paper, the equilibrium geometries of two isomers of the newly found compound ——nitrosomethanol——have been optimized by ab initio SCF MO method with 3-21G basic set by gradient technique. And the second derivatives of potential energy (i. e. the force constant matrix elements) have been calculated analytically. Hence the entire force fields of the two isomers of nitro- somethanol have been obtained theoretically. The theoretical vibrational frequencies and the corres- ponding normal modes were obtained and compared with the experimental values. and the structures of two isomeric forms of nitrosomethanol are established.

Optimal Bandgap of Double Perovskite La-Substituted Bi2FeCrO6 for Solar Cells:an ab initio GGA+U Study

The ab initio generalized gradient approximation (GGA)+U study of multiferroic (La Bi )2FeCrO6 in pnma structure and ferri-magnetic order, including Hubbard corrections ( eV) for transition metal/rare earth d-electrons with 20 atoms cell, shows optimum local magnetic moments of (Cr , Fe equal to (−2.56, 4.14) μB and an ideal spin-down band gap of 1.54 eV. Tuned-band gap La-substituted double oxide perovskites BFCO should exhibit enhanced visible-light absorption and carrier mobility, thus could be convenient light absorbers and then efficient alternatives to wide-gap chalcopyrite absorber-based solar cells failing to achieve highest power conversion efficiencies, and even compete with their metal-organic halide perovskites counterparts.

AB INITIO STUDIES ON THE INTERACTION BETWEEN CH_3OH AND H_2CO

The interaction between CH_3OH and H_2CO has been studied by ab initio method(6-311G basis set).It has been found that there are two possible complexes:(Ⅰ)H-bond Brnsted complex CH_3OH...OCH_2(Ⅱ)Donor scceptor Lewis complex CH_3OH...CH_2P.HF/6-311G stabilization energies for complex(Ⅰ)and complex(Ⅱ)are 25.1 and 17.1 kJ/mol respectively.

AB INITIO STUDIES ON THE REACTION MECHANISH OF CYCLOADDITION OF KETENE AND FORMALDEHYDE

The cycloaddition reaction of ketene and formaldehyde,lesding to 2- oxetanone,has been studied theoretically by means of RHF/3-21G.This reaction is believed to be nonsynchronous but concerted,taking place through a twisted four membered ring transition state.Two types of frontier orbital interactions are involved in this reaction.The activation barrier is calculated to be 123.1KJ/mol (MP2/3-21G result).