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用量子力学方法获得分子的模型力场现已占有很重要的位置.然而由于理论上很难获得体系高精度解析势能面,使力场的理论计算遇到了困难.直到Pulay提出梯度法后,量子化学方法才被广泛用于多原子分子的振动分析.但由于该方法采用数值微分通过能量的第二阶导数所获得的力场矩阵对角元误差很大,需将其伸缩、变角对角力常数分别扣除10％、20％,才能获得与观测值相近的结果;且ab initio计算花机时太多,应用于大分子计算存在一定的困难.为此本文把前文提出的确定力常数的模型势函法与MNDO、MINDO/3等半经验方法结合起来,构造多原子分子的力场,并用于振动分析,获得了满意的结果.
However, due to the difficulty in theoretically obtaining the accurate analytic potential energy surface of the system, the theoretical calculation of the force field has encountered difficulties. Until Pulay proposed the gradient method, the quantum The chemical method is widely used in the vibration analysis of polyatomic molecules.But because of the error of the matrix of the force field obtained by the numerical derivation of the second derivative of energy by numerical differentiation, the telescoping, And the constants are respectively deducted by 10% and 20% respectively to get the result similar to the observed value.And when ab initio is too large, it is difficult to calculate the macromolecule.To this end, Potential function method combined with MNDO, MINDO / 3 and other semi-empirical methods to construct the force field of polyatomic molecules, and used for vibration analysis, and obtained satisfactory results.