用第一性原理方法获取周期体系中原子的部分电荷

利用量子化学软件包Crystal计算了立方周期性边界条件下液态水体系的静电势(ESP)和静电场(EF).在此基础上,提出了一种由第一性原理方法获取周期体系中原子的部分电荷的快捷方法.该方法把由周期性边界条件引入的平均静电势准mean作为一个拟合参数,通过对第一性原理静电势与Ewald加和法静电势的最小二乘法拟合而实现.值得说明的是,比较静电势与静电场拟合方法,前者的相对拟合误差仅为2%-3%,比后者小一个数量级.考察了四种电荷限制条件下,静电势、静电场拟合的水分子原子部分电荷及偶极矩的分布情况.

Atomic Partial Charges for Periodic Systems from First-Principles Calculations

We calculated the electrostatic potential (ESP) and electric field (EF) of periodic liquid water systems using the quantum chemistry software package, Crystal. We proposea method to obtain atomic partial charges rapidly for periodic systems based on first-principles calculations. In this method, the average electrostatic potential φ^mean, which is introduced to meet the periodic boundary condition, is taken as a parameter during the least squares fitting of the ESP from first-principles calculations and used in the Ewald summation. A comparison of the two methods, i.e., ESP and EF fitting, reveals that the relative root mean-square deviation (RMS) of the former method is only 2%-3%, which is one order of magnitude smaller than that of the latter method. In addition, the distribution of the derived atomic partial charges and dipole moments for the water system are discussed using four charge restrained fits.