一种对大体系局部进行高精度量子化学计算的新方法

A New Method for Performing High Accurate Quantum Chemical Calculations in a Local Area of Large Systems

提出一种可以对大体系的局部区域进行高精度量子化学计算的新方法 .将体系划分为活性区和环境区 ,采用比较粗略的算法获得大体系的密度矩阵 ,通过基组的变换将密度矩阵分解为对应于活性区与环境区的子矩阵的直和 ,活性区和环境区分别拥有整数个电子 ,成为相对独立的化学键饱和的子体系 .然后冻结环境区密度矩阵 ,同时考虑环境区在活性区所产生势场的作用 ,对活性区进行高精度的量子化学计算 .对一些分子进行计算 ,得到的电荷分布、键长、键断裂能、电离势与电负性等与对大体系整体进行高精度计算得到的结果相当一致 ,而计算量减少很多 ,表明提出的方法可行 。

A new method is presented to perform high accurate quantum chemical calculations in a local area of large systems. The system is partitioned into the active and surrounding areas. A comparatively rough calculation is performed for the system to produce the approximate density matrix and it is transformed into a direct sum of the submatrices related to the active and surrounding areas, respectively, which involve integer electrons and form relatively independent subsystems with saturated chemical bonding. Then the surrounding area is frozen, and high accurate quantum chemical calculations are performed in the active area with the action of the potential produced by the charge in the surrounding area being taken into account. The calculations have been performed for a series of organic molecules by use of the proposed method, and the data of Mulliken charges, bond lengths, bond dissociation energies, the first ionization energies and electronegativities are obtained, which are in satisfactory agreement with those obtained from the high accurate calculations of the whole systems, while the computational effort of the former is considerably reduced comparing to the latter. It can be concluded that the proposed method is practical and valuable.