偏分势能面及其应用(Ⅰ):概念、构造方法及几个简例

提出了偏分势能面的概念,偏分势能面可由完全势能面抽取出来,也可采用ab initio方法进行构造．作为范例。给出了F H2→FH H,H H2→H2 H,I HI→IH I及Na I2→Na^ I2^-等体系中几种偏分势能面的构造和应用．可以看到,应用偏分势能面对于分析反应机理及散射共振态的生成方面显示突出优点．     

两体扰动势和H2O通道反应的三原子体系解析势

提出了两体扰动势的概念.通过两体扰动势构造多原子相互作用体系解析势的理论方法,获得了非线性三原子H2O相互作用体系的解析势函数.用势能面正确描述了O(1D)+H2→H2O→OH+H通道反应的性质.理论分析和实验结果非常符合.该方法比较容易推广构造多原子相互作用体系解析势.     

I+HI(v=0)→IH(v′=0)+I体系散射共振态的理论研究

在 QCISD ( T) / / MP2水平下 ,分别采用 6-3 1 1 ++G* * 基组和 SDD基组对重 -轻 -重反应 I+HI(ν=0 )→ IH(ν′=0 ) +I中的 H和 I的偏分势能面进行了 ab initio计算 ,指认出在 0～ 0 .5 8e V碰撞能范围内所产生的 6个散射共振态为 Feshbach共振 ,并与文献报道的量子散射理论计算与高分辨阈值光分离光谱实验结果进行了比较 .     

两体扰动势和H2O通道反应的三原子体系解析势

提出了两体扰动势的概念.通过两体扰动势构造多原子相互作用体系解析势的理论方法,获得了非线性三原子H2O相互作用体系的解析势函数.用势能面正确描述了O（1D）＋H2→H2O→OH＋H通道反应的性质.理论分析和实验结果非常符合.该方法比较容易推广构造多原子相互作用体系解析势.     

一种计算Feshbach共振态寿命的新方法

在自然碰撞坐标下构建偏分势能面, 利用数值传播方法求解沿反应坐标的核运动方程, 然后用过渡态波函数的相移因子构造反应体系共振态寿命矩阵. 这是一种直接计算化学反应散射共振寿命的量子散射方法. 用此方法计算了I+HI(υ)→IH(υ’)+I体系的第一散射共振态寿命, 所得数值与Neumark 的高分辨阈值光分离光谱实验的结果相一致.     

I＋HI（y=0）→IH（y′=0）＋I体系散射共振态的理论研究

在QCISD(T)//MP2水平下，分别采用6-311 G基组和SDD基组对重-轻-重反应I HI(p=0)→IH(√=0) I中的H和I的偏分势能面进行了abinitio计算.指认出在0～0.58eV碰撞能范围内所产生的6个散射共振态为Feshbach共振，并与文献报道的量子散射理论计算与高分辨阈值光分离光谱实验结果进行了比较.     

NO3-+Cl2→ClONO2+Cl-反应势能面和势能阱

采用密度泛函理论B3LYP方法和6-311+G(d)基组, 计算构建离子-分子气相反应NO3-+Cl2→ClONO2+Cl-的三维势能面. 三维反应势能面证明该反应没有过渡态和势能垒, 但是存在一个深达-55.0 kJ/mol的势能阱(以氯气分子和硝酸根离子相隔无穷远为参量). 在势能阱底部, 有个化合物(O2NOClCl)- 称为势阱化合物, 依赖于势能阱而稳定存在. 理论红外光谱预测低温红外光谱能检测该势阱化合物. 低温条件下, 该反应由热力学控制, 反应产物是势阱化合物(O2NOClCl)-. 当温度升高, 该反应由动力学控制, 势阱化合物(O2NOClCl)-不稳定, 发生分解反应, 重新生成NO3-和Cl2. 研究结果可用来解释低温时ClONO2与Cl-气相反应不能产生Cl2的原因.     

用神经网络方法拟合的反应体系H＋CH4←→H2＋CH3的一个全域势能面

利用神经网络力法,基于47783个高精度从头算能量点构建了反应体系H＋CH4←→H2＋CH3的一个全域势能面．通过大最的准经典轨线以及量子散射计算测试了势能面的收敛性质．这个势能面对于拟合过程以及从头算点的数目都已经完全收敛,拟合误差很小县比Shepard插值的势能面计算速度更快,代表了此标志性多原子反应体系最好的势能面．     

氟原子与氢分子共线反应几率的量子散射计算

基于最新的6SEC势能面,用邓从豪等提出的LCAC-SW方法计算得到了共线反应F+H~2(v=0)→HF(v')+H的态-态反应几率,计算结果准确地反映出势能面的特点,进一步证明LCAC-SW方法是一成功的量子散射方法。     

锂(100)面上H_2H+H反应动力学的理论研究

本文在H-Li(100)面吸附扩散的ab initio SCF势能面基础上构造了(H_2H+H)/Li(100)面相互作用的推广LEPS势能面,并用QCT方法研究了该体系的反应动力学行为。分析势能面特征得到:H_2在Li(100)面上的吸附无需活化能,H_2在Li(100)面上的解离吸附与吸附位及吸附模式密切相关,H_2的卧式解离比立式解离要容易得多。分析各种碰撞轨迹得到:低覆盖度下双氢原子的表面复合几率很小,H_2的表面解离几率受到H_2振动量子数的控制。本文构造了一种适合于动力学研究的气体-金属表面相互作用势能面,并且,动力学QCT计算结果能够对H_2表面活化的分子束实验作出合理的解释。     

CN~+分子势能函数和光谱常数的多参考组态相互作用方法研究

采用多参考组态相互作用方法和aug-cc-p V5Z基函数组计算了CN+分子11∑+,21∑+,13∑+和13Π电子态的势能曲线。利用MS势能函数拟合得到了相应的解析势能表达式。在此基础上求解CN+分子的核运动薛定谔方程,获得了全部振动和转动能级,并用Dunham系数展开式拟合出了光谱常数,与目前仅有的11∑+,21∑+态的文献报道结果进行了比较。结果可对航天尾气及工业过程光谱方法监控提供参考。     

An analytic potential energy function for the amide–amide and amide–water intermolecular hydrogen bonds in peptides

An analytic potential energy function is proposed and applied to evaluate the amide–amide and amide–water hydrogen‐bonding interaction energies in peptides. The parameters in the analytic function are derived from fitting to the potential energy curves of 10 hydrogen‐bonded training dimers. The analytic potential energy function is then employed to calculate the N? H…O?C, C? H…O?C, N? H…OH₂, and C?O…HOH hydrogen‐bonding interaction energies in amide–amide and amide–water dimers containing N‐methylacetamide, acetamide, glycine dipeptide, alanine dipeptide, N‐methylformamide, N‐methylpropanamide, N‐ethylacetamide and/or water molecules. The potential energy curves of these systems are therefore obtained, including the equilibrium hydrogen bond distances R(O…H) and the hydrogen‐bonding energies. The function is also applied to calculate the binding energies in models of β‐sheets. The calculation results show that the potential energy curves obtained from the analytic function are in good agreement with those obtained from MP2/6‐31+G** calculations by including the BSSE correction, which demonstrate that the analytic function proposed in this work can be used to predict the hydrogen‐bonding interaction energies in peptides quickly and accurately. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Smoothing techniques of global optimization: Distance scaling method in searches for most stable Lennard–Jones atomic clusters

Spatial averaging of the potential energy function facilitates the search for the most stable configuration of a molecular system. Recently some global optimization methods of this kind have been designed in the literature that rely on physical phenomena such as diffusion, wave function evolution in quantum mechanics, Smoluchowski dynamics, evolution in temperature of canonical ensembles, etc. In the present article we highlight the fact that all these methods, when applied to the Gaussian distributions of an ensemble, represent special cases of a set of differential equations involving the spatially averaged potential energy. Their structure suggests that the nature's strategy to cope with the global optimization is robust and differs only in the details in particular applications. The strategy consists of going downhill of the averaged potential energy, removing the barriers, and hunting for low energy regions by a selective increasing of the spatial averaging. In this study we explore the deformation of the potential rather than its averaging. The deformation comes from scaling of atomic distances and reduces the barriers even more effectively than the Gaussian averaging. The position and widths of the Gaussian distribution evolve similarly to the Gaussian density annealing (GDA), but we allow elliptical instead of spherical Gaussians as well as branching of the single trajectory of the system into multiple ones. When the temperature reaches 0 K, one has a number of independent Gaussian distributions, each corresponding to a structure and (usually low) energy of the system. The multiple elliptic-Gaussian distance scaling method has been applied to clusters of argon atoms (N=5,…,31), a system serving usually as a benchmark domain. The method found the global minima for all but three clusters (of very low energy). The procedure is 20 or more times less expensive than the GDA one. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 2040–2049, 1997     

Theoretical Studies on the Potential Energy Surface and Vibrational Energy Levels of HXeBr

The potential energy surface for the electronic ground state of the HXeBr molecule is constructed from more than 4200 ab initio points calculated using the internally contracted multi-reference configuration interaction method with the Davidson correction （icMRCI ＋ Q）. The stabilities and dissociation barriers are identified from the potential energy surface. The three-body dissociation channel is found to be the dominant dissociation channel for HXeBr. Low-lying vibrational energy levels of HXeBr calculated using the Lanczos algorithm are found to be in good agreement with the available experimental band origins.     

Interaction energy contours of molecules as probed by a test atom

Potential energy contour curves for some simple molecules interacting with a test atom (a Li atom in the ground state) are calculated by theab initio method. Relative hardness of the repulsive molecular surface is found to be anisotropic. This indicates that the outer boundary surface of a molecule changes its form depending on the extent of applied external forces. The attractive nature of the molecular surface is demonstrated to be local. Surroundings of electronegative atoms having nonbonded electron pairs are found to be attractieve to the test atom having both electron-donating and electron-accepting abilities.     

Nonbonding pairs in cyclic thioethers: Electrostatic modeling and ab initio calculations for complexes of 2,5-dihydrothiophene,thietane, and thiirane with hydrogen fluoride

Electrostatic potential energies V(ϕ) of a non-perturbing, protonic charge at fixed distances r from the S atom in three cyclic thioethers were examined as functions of the angles ϕ made by the r-vector with the C₂ axis (thiirane and 2,5-dihydrothiophene) or the local C₂ axis (thietane). The electrostatic PE V_HF(ϕ) of HF (HF modelled as an extended electric dipole) was also calculated and the results compared with geometries of the thioether⋯HF complexes calculated at the CCSD(T)-F12c/cc-pVTZ-F12 level. The latter reveal angular deviations θ ∼10-20° of the S⋯H F nuclei from collinearity in directions suggesting secondary interactions of F with H atom(s) of the rings. Angles ϕ made by the S⋯H hydrogen bond with the C₂ (or local C₂) axes in the complexes are systematically larger (∼4-9°) than indicated by the V_HF(ϕ) functions. Minima in the simple V(ϕ) versus ϕ functions occur at values smaller (∼5-10°) than those in the V_HF(ϕ) curves.     

CCSD(T) and MRCI studies on the ground and excited states of BrOClO and ClOBrO

In this work, three forms (cis, trans and nonplanar) of ClOBrO and BrOClO were optimized at CCSD(T)/cc‐pVTZ level of theory. At the most stable forms (nonplanar form) of ClOBrO and BrOClO, the vertical excitation energies for the lowest six singlet states and two triplet states were calculated at the multireference internally contracted configuration interaction (MRCI) level of theory using cc‐pVDZ, Aug‐cc‐pVDZ, cc‐pVTZ, and Aug‐cc‐pVTZ basis sets. The scalar relativistic effect on the excited states of BrOClO and ClOBrO were estimated. In addition, the potential energy curves of the lowest six singlet states and two triplet states of BrOClO and ClOBrO, as well as BrOOCl were calculated at both MCSCF (complete active space self‐consistent field) and MRCI levels of theory using Aug‐cc‐pVDZ basis set on the active space (18e,12o) along the distances of BrO? ClO, ClO? BrO, and BrO? OCl. The results were compared among BrOOCl, ClOBrO, and BrOClO. The first singlet excited state of BrOOCl is 1.12 eV higher than that of BrOClO and 1.36 eV higher than that of ClOBrO at MRCI/cc‐pVTZ level of theory. The first triplet excited state of BrOOCl is 0.77 eV higher than that of BrOClO and 0.86 eV higher than that of ClOBrO at MRCI/cc‐pVTZ level of theory. Most of the excited states of BrOClO studied in this work are unbound states; but most of the ClOBrO and BrOOCl excited states studied in this work are weakly bound states at MRCI level of theory. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Potential energy function based on the narcissus constant,its square and its cube

The narcissus constant, N = 2.3983843828..., is defined as a number that fulfills the narcissistic infinite nested radical equation

Theoretical studies on the potential energy surfaces and vibrational energy levels of HXeF and HXeCl

The potential energy surfaces for the electronic ground state of the HXeCl and HXeF molecules areconstructed by using the internally contracted multi-reference configuration interaction with theDavidson correction(icMRCI Q)method and large basis sets.The stabilities and dissociation barriersare identified from the potential energy surfaces.The three-body dissociation channel is found to bethe dominate dissociation channel for HXeCl,while two dissociation channels are possible and com-petitive for HXeF.Based on the obtained potentials,vibrational energy levels of HXeCl and HXeF arecalculated using the Lanczos algorithm.Our theoretical results are in good agreement with the avail-able observed values.Particularly,the calculated fundamental frequency of the H—Xe stretching vi-bration including the Xe matrix effect of HXeCl is found to be 1666.6 cm-1,which is only 17.6 cm-1higher than the recently observed value of 1649 cm-1.     

Theoretical investigations on analytical potential energy function and spectroscopic parameters for the state b3Πu of dimer 7Li2

The SAC‐CI (symmetry‐adapted‐cluster configuration‐interaction) method presented in Gaussian 03 program package is applied to investigate the adiabatic potential energy curves (PECs) of ⁷Li₂(b³Π_u). These calculations are performed at numbers of basis sets, such as 6‐311++G(3df,3pd), 6‐311++G(2df,2pd), 6‐311++G(df,pd), D95V++, D95(3df,3pd), D95(d,p), cc‐PVTZ, 6‐311++G and 6‐311++G(d,p). All the ab initio calculated points are fitted to the analytic Murrell‐Sorbie functions and then used to compute the spectroscopic parameters. The analytic potential energy function (APEF) for this b³Π_u state is reported. By comparison, the spectroscopic parameters reproduced by the APEF attained at 6‐311++G(2df,2pd) are found to be very close to the latest experimental findings. With the APEF obtained at the SAC‐CI/6‐311++G(2df,2pd) level of theory, a total of 62 vibrational states is found when J = 0. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants for these vibrational states are also reported. The reasonable dissociation limit for this state is deduced using the calculated results at present. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007