基态Li_n(n=2,3)结构与完全解析势能函数

使用Gaussian03程序包,采用全电子单双取代耦合簇(CCSD(full))方法,选择基组6-311+g(2df),对Li2分子的基态进行优化计算,采用十一参量Murrell-Sorbie函数,运用最小二乘法拟合得到Li2分子基态解析势能函数,给出与实验值符合很好的光谱常数;使用同样的方法和基组,对Li3分子的基态结构进行优化计算,得到Li3分子基态平衡结构.采用多体项展式法,利用Li3分子平衡结构C2v的几何参数、力常数和离解能,以及七个线性系数Ci(i=1,2,3,4,5,6,7)与两个非线性系数的函数关系,进行非线性优化拟合得到两个非线性系数,进而得到七个线性系数,得到Li3分子基态完全解析势能函数.势能面静态特征表明,该势能函数再现了Li3分子基态全部平衡结构特征.

Structures and analytic potential energy functions for ground state of Lin (n=2, 3) molecules

The molecular structures of ground state of Li2 are calculated on the level of 6-311+g (2df) basis set using CCSD(full) method in Gaussian03 programs. Its potential energy functions have been derived by the least-square fitting method and the eleven-parameter Murrell-Sorbie function, and the obtained spectroscopic constants are in good agreement with the experimental values; The ground state structures of Li3 have been optimized by the same method and basis set. By using the geometric parameters of Li3 molecular balance structure C2v, the force constant, dissociation energies and the function relations of the linear and nonlinear coefficients, and in terms of a nonlinear optimization fitting made in the near minimum point of Li3 molecular potential energy surface, the nonlinear coefficients and then the linear coefficients Ci (i=1, 2, 3, 4, 5, 6, 7) are obtained. With the many-body expansion, the completely analytical potential energy functions of ground state of the Li3 molecular are also derived. The ground state equilibrium geometries of Li3 are reproduced by the completely potential energy functions and shown in the potential energy surfaces.