Ab initio potential energy surface and anharmonic vibration spectrum of NF_(3)^(+)

Potential energy surfaces(PESs), vibrational frequencies, and infrared spectra are calculated for NF_(3)^(+) using ab initio calculations, based on UCCSD(T)/cc-p VTZ combined with vibrational configuration interaction(VCI). Based on an iterative algorithm, the surfaces(SURF) program adds automatic points to the lattice representation of the potential function, the one-dimensional and two-dimensional PESs are calculated after reaching a convergence threshold, finally the smooth image of the potential energy surface is fitted. The PESs accurately account for the interaction between the different modes, with the mode q_(6) symmetrical stretching vibrations having the greatest effect on the potential energy change of the whole system throughout the potential energy surface shift. The anharmonic frequencies are obtained when the VCI matrix is diagonalized. Fundamental frequencies, overtones, and combination bands of NF_(3)^(+) are calculated, which generate the degenerate phenomenon between their frequencies. Finally, the calculated anharmonic frequency is used to plot the infrared spectra.Modal antisymmetric stretching ν_(5) and symmetric stretching ν_(6) exhibit a phenomenon of large-intensity borrowing. This study can provide data to support the characterization in the laboratory.

Ab initio molecular dynamics simulation reveals the influence of entropy effect on Co@BEA zeolite-catalyzed dehydrogenation of ethane

The C–H bond activation in alkane dehydrogenation reactions is a key step in determining the reaction rate.To understand the impact of entropy,we performed ab initio static and molecular dynamics free energy simulations of ethane dehydrogenation over Co@BEA zeolite at different temperatures.AIMD simulations showed that a sharp decrease in free energy barrier as temperature increased.Our analysis of the temperature dependence of activation free energies uncovered an unusual entropic effect accompanying the reaction.The unique spatial structures around the Co active site at different temperatures influenced both the extent of charge transfer in the transition state and the arrangement of 3d orbital energy levels.We provided explanations consistent with the principles of thermodynamics and statistical physics.The insights gained at the atomic level have offered a fresh interpretation of the intricate long-range interplay between local chemical reactions and extensive chemical environments.

Convergence Issues Associated with Cutoff Energies and Ab Initio Studies of Adsorption of CO on W and Pt

The experimental research programs of 1950s, to understand the adsorption of CO on W surfaces, changed to ab initio studies in 2000s. The goals were to seek improved practical applications. Most of the studies were based on density functional theory. Many studies also used programs, such as VASP (Vienna Abinitio simulation package) and CPMD. The computational procedures used plane wave approximations. This needed studies with selection of K points and cutoff energy selection to assure convergence in energy calculations. Observations and analysis of papers published from 2006 to 2022 indicate that the cutoff energies were selected arbitrarily without any needed convergence studies. By selecting a published 2006 paper, this paper has clearly showed that an arbitrary selection of cutoff energy, such as 460 eV, is not in the range of, cutoff energies that assure convergence of energy calculations, with ab initio methods and have indicated correction procedures. .

Ab initio study of chemical effect on structural properties of Ti–Al melts

We study chemical effect on the structural properties of Ti–Al melts, with the Al concentration systematically changed,via ab initio molecular dynamics simulations. By calculating the partial coordination numbers, we find a preferred connection between the nearest neighbors for Al–Ti pairs. This induces an excess Ti coordination in the cluster characterized by local five-fold symmetry in Voronoi tessellation. Structural entropy measured from the diversity of Voronoi polyhedrons shows an intriguing non-monotonic tendency with concentration: it first decreases to a minimum value at Ti_(40)Al_(60), and then increases beyond this concentration. This implies a more ordered local structure induced by the chemical interaction at the intermediate compositions. The spatial correlation among the crystalline-like or the icosahedral-like clusters also exhibits the highest intensity for Al–Ti pairs, verifying the important role played by the chemical interaction in the local structure connectivity.

Ab initio Study on Ionization Energies of 3-Amino-1-propanol

Fourteen conformers of 3-amino-1-propanol as the minima on the potential energy surface are examined at the MP2/6-311＋＋G＊＊ level. Their relative energies calculated at B3LYP, MP3 and MP4 levels of theory indicated that two most stable conformers display the intramolecular OH - N hydrogen bonds. The vertical ionization energies of these conformers calculated with ab initio electron propagator theory in the P3/aug-cc-pVTZ approximation are in agreement with experimental data from photoelectron spectroscopy. Natural bond orbital analyses were used to explain the differences of IEs of the highest occupied molecular ortibal of conformers. Combined with statistical mechanics principles, conformational distributions at various temperatures are obtained and the temperature dependence of photoelectron spectra is interpreted.

Ab initio Study on Spectral Properties of Charge-Compensated Ce^3＋ in NaF

We report an ab initio〉/I〉 study of spectral properties of Ce^3＋ doped at Na＋ site of the NaF crys-tal, with the charge imbalance compensated by two oxygen substitutions for fluoride （OF＇） in the first coordination shell or two sodium vacancies （VNa＇） in the second coordination sphere. Density functional theory calculations within the supercell model are first performed to op-timize the local structures of the charge-compensated Ce^3＋, based on which Ce-centered embedded clusters are constructed and wave function-based CASSCF/CASPT2/RASSI-SO calculations are carried out to obtain the energies of 4f1 and 5d1 levels. By comparing the calculated 4f→5d transition energies with experimental excitation spectra at low temper-atures, the lowest 4f→5d transition band peaked at 390 nm is assigned to the Ce^3＋ with charge compensation by two coordinating OF＇ substitutions, rather than to the Ce^3＋ with compensation by two VNa0 vacancies, as proposed earlier. The electronic reason for the large redshift （by -8000 cm-1） of the lowest 4f→5d transition as induced by the two nearby OF＇ substitutions is analyzed in terms of the changes in the centroid shift and crystal-field splitting.

Ab initio Study of Hyperconjugative Effect on Electronic Wavefunctions of 2-chloroethanol

The electronic structure of five conformers of 2-chloroethanol was studied by ab initio calculations at B3LYP and MP2 levels of theory with aug-cc-pVTZ basis set. The existing hydrogen bond and hyperconjugation effects on the stability of 2-chloroethanol conformers were discussed on the base of natural bond orbital analyses. The result exhibits that hyperconjugation is the main factor to determine the stability of conformers. Such effects on the electron wavefunctions of the highest-occupied molecular orbital （HOMO） of different conformers are demonstrated with electron momentum spectroscopy, exhibiting the obviously different symmetries of the HOMO wavefunctions in momentum space.

Linear correlations of formation enthalpies/bulk modules and atomic volumes observed in Pt-Zr compounds by ab initio calculation

118 kinds of Pt-Zr phases were established and investigated by considering various structures. Then the related physical properties, such as structural stability, lattice constants, formation enthalpies, elastic constants and bulk moduli, are obtained by ab initio calculations. Based on the calculated results of formation enthalpies, the ground-state convex hull is derived for the Pt-Zr system. The calculated physical data would provide a basis for further thermodynamic calculations and atomistic simulations. For these Pt-Zr compounds, it is found there are a positive linear correlation between the formation enthalpies and atomic volumes, and a negative linear correlation between the bulk modules and atomic volumes.

8-羟基喹啉铝光电性质的Ab initio和DFT研究

利用 ab initio HF和密度泛函理论 B3L YP等方法 ,对金属有机配合物 8-羟基喹啉铝 (Al Q3)进行几何结构优化 ,探索分子内部电子跃迁的机理 .结果表明 ,电子从基态跃迁到低激发态时主要为π-π* 跃迁 ;电荷从含氧的苯酚环转移至含氮的吡啶环上 ,包括两环之间 C→ C转移和 O→ N转移 ,与金属离子关系不大 .考虑到配体对发光性质的贡献 ,进一步设计了 3种 Al Q3的衍生物 .

硝酸甲酯分子间相互作用的DFT和ab initio比较

用密度泛函理论(DFT)和从头算(abinitio)方法,分别在B3LYP/6-31G和HF/6-31G水平上求得硝酸甲酯三种二聚体的全优化几何构型和电子结构,并用6-311G和6-311++G基组进行总能量计算.对HF/6-31G计算结果进行MP4SDTQ电子相关校正.在各基组下均进行基组叠加误差(BSSE)和零点能(ZPE)校正求得结合能.对6-31G优化构型作振动分析并基于统计热力学求得200～600K温度下单体和二聚体的热力学性质.详细比较两种方法的相应计算结果,发现DFT求得的分子间距离较短,分子内键长较长,所得结合能均小于相应abinitio计算值.

Cu^+和Ag^+叠氮盐晶体的周期性ab initio计算

The energy bands,electronic structures of CuN3 and AgN3 crystallines were investigated by periodic ab initio method.The charge density projection shows that there are overlaps of isodensities between the terminal nitrogen and metallic ion,indicating that the metals and the azides are combined by covalent bonds.The crystal lattice energies are-781.05 and-840.83 kJ/mol for CuN3 and AgN3 respectively.These results approach the data obtained by Gray′s approximate method.The frontier crystal orbital mainly consists of the atomic orbital of azide′s terminal nitrogen.The energy gap for AgN3 is smaller than that of CuN3,and the highest occupied crystal orbitals of AgN-3 consist of both the atomic orbitals of the terminal nitrogen in azide and the silver ion,which facilitates the electron to leap from terminal nitrogen in azide to metallic ion directly.Hence silver azide is slightly more sensitive than copper azide.The elastic coefficients C11,C22 and C33 of CuN3 are predicted to be 96.52,96.86 and 154.06 GPa,C11 and C22 of AgN3 are 303.29 and 138.80 GPa.

硝酸乙酯分子间相互作用的ab initio研究

在abinitio HF/ 6 31G 水平上求得硝酸乙酯二聚体势能面上的四种优化构型和电子结构 .经MP2电子相关校正和基组叠加误差 (BSSE)以及零点能 (ZPE)校正 ,求得二聚体的最大结合能为 11.46kJ·mol-1.还进行HF/ 6 311G 和HF/ 6 311++G 水平的总能量比较计算 ,发现 6 31G 基组对计算结合能比较适合 .二子体系间的电荷转移很少 .对优化构型进行振动分析 ,并基于统计热力学求得从单体形成二聚体的热力学性质变化 .

簇模型选取的配位数原则——CO/ZnO吸附体系的ab initio研究

提出并以ＺｎＯ为例初步考察了用于金属氧化物的簇模型选取的配位数原则，即尽可能选取边界悬空键总数最少的簇模型，使簇模型“边界效应”尽可能低．在此基础上研究了ＣＯ在一系列按配位数原则选取的（ＺｎＯ）ｎ表面簇模型上的吸附行为．结果表明，配位数原则有效地缩小了簇模型的选取范围；依配位数原则确立的ＺｎＯ表面簇模型，能够对ＣＯ／ＺｎＯ吸附体系给出合理的定性解释．计算还表明，考虑相关效应有助于进一步改善计算结果．

嵌锂石墨充放电机制的ab initio和DFT理论研究

用abinitio/HF和DFT/B3LYP方法探究了在锂离子二次电池中锂离子在石墨负电极材料里可逆嵌脱过程 .理论计算结果表明 ,嵌锂石墨LIG (lithiumintercalatedgraphite)充放电机制是锂在石墨碳层间可逆嵌脱 ,同时伴随着锂与碳层间发生电荷连续转移和碳层堆积方式改变的协同过程 ;计算结果也明确证实 ,嵌锂石墨嵌入脱出锂离子的过程就是锂离子二次电池储存与释放能量的过程 .提出的嵌锂石墨充放电机制较好地丰富了固体电解质相界面SEI (solidelectrolyteinterphase)

CH_3F分子间相互作用的ab initio研究

在 MP2 /6-31 1 ++G( 3d,3p)电子相关校正水平上 ,对 CH3F二聚体可能存在的几何构型进行全自由度能量梯度优化和频率验证 ,发现 3种势能面上有极小点的构型 .进一步在高级电子相关校正的 MP4 S-DTQ、CCSD( T) /6-31 1 ++G( 3df,3pd)方法水平上 ,对其中总能量最小的构型进行精确计算 ,得到二聚体的结合能为 -9.70 7k J/mol.研究结果支持了由光谱实验结果推测的构型 ,解释了

取代基对氮自由基稳定性影响的ab initio研究

用UHF／4-31G基组，全构型优化，研究了九个氮自由基NHR（R＝CH3，CF3，CCl3，CN，NH2，CHO，OH，COOH，F）的构型和稳定化能ΔE，它们的ΔE分别为25．24，－38．53，－20．59，21．46，19．96，58．82，73．69，31．75，63．85kJ·mol-1，表明，除CF3，CCl3以外，其余七个取代基对氮自由基起稳定化作用．

ab initio CALCULATION FOR THE ELECTRONIC STRUCTURE OF GaAs/Al_xGa_(1-x) As SUPERLATTICES: CONJUGATE GRADIENT APPROACH

The electronic structure of GaAs/Al xGa 1-x As superlattices has been investigated by an ab initio calculation method—the conjugate gradient (CG) approach.In order to determine that,a conventional CG scheme is modified for our superlattices:First,apart from the former scheme,for the fixed electron density n(z),the eigenvalues and eigenfunctions are calculated,and then by using those,reconstruct the new n(z).Also,for every k z,we apply the CG schemes independently.The calculated energy difference between two minibands,and Fermi energy are in good agreement with the experimental data.

氧化钼催化剂的ab initio MO研究

采用原子簇模型,用从头计算分子轨道方法研究了模拟MoO3(010)晶面的几个簇Mo2O11H10、Mo3O16H14和Mo7O32H22,在RHF/MINI/ECP-SBK或UHF/3-21G/ECP-SBK水平上对其结构进行了完全优化,得到了MoO3(010)面上三种结构不等价氧的成键特性、电子性质以及轨道布居等结构性质。发现结构不等价氧与钼原子的成键特性是有差异的,且轨道布居等数据可以为解释在丙烯选择氧化为丙烯醛的反应中,氧亲核插入烯丙基过程中的活性位提供信息。

Ab Initio Calculations of the Electronic Structures of Copper Pyrites CuS2, CuSe2 and CuTe2

The electronic structures of CuS2, CuSe2 and CuTe2 with pyrite structures, within the framework the density-functional theory have been investigated. The calculated results explained the recent experimental results which show that there is no clear indication of strong electron correlations in the electronic properties of Cu pyrites, due to the dominant chalcogen p character rather than d characteristic of Cu at the Fermi level.

Ab initio calculations of accurate dissociation energy and analytic potential energy function for the second excited state B^1∏ of ^7LiH

The reasonable dissociation limit of the second excited singlet state B1∏ of ^7LiH molecule is obtained. The accurate dissociation energy and equilibrium geometry of the B^∏ state are calculated using a symmetry-adaptedcluster configuration interaction method in full active space. The whole potential energy curve for the B1H state is obtained over the internuclear distance ranging from about 0.10 nm to 0,54 nm, and has a least-square fit to the analytic Murrell-Sorbie function form. The vertical excitation energy is calculated from the ground state to the B^1∏ state and compared with previous theoretical results. The equilibrium internuclear distance obtained by geometry optimization is found to be quite different from that obtained by single-point energy scanning under the same calculation condition. Based on the analytic potential energy function, the harmonic frequency value of the B^1∏ state is estimated. A comparison of the theoretical calculations of dissociation energies, equilibrium interatomic distances and the analytic potential energy function with those obtained by previous theoretical results clearly shows that the present work is more comprehensive and in better agreement with experiments than previous theories, thus it is an improvement on previous theories.