Takahashi Hideaki, Umino Satoru, Morita Akihiro
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578, Japan.
J Chem Phys. 2015 Aug 28;143(8):084104. doi: 10.1063/1.4928762.
We developed a simple method to calculate exchange repulsion between a quantum mechanical (QM) solute and a molecular mechanical (MM) molecule in the QM/MM approach. In our method, the size parameter in the Buckingham type potential for the QM solute is directly determined in terms of the one-electron wave functions of the solute. The point of the method lies in the introduction of the exchange core function (ECF) defined as a Slater function which mimics the behavior of the exterior electron density at the QM/MM boundary region. In the present paper, the ECF was constructed in terms of the Becke-Roussel (BR) exchange hole function. It was demonstrated that the ECF yielded by the BR procedure can faithfully reproduce the radial behavior of the electron density of a QM solute. The size parameter of the solute as well as the exchange repulsion are, then, obtained using the overlap model without any fitting procedure. To examine the efficiency of the method, it was applied to calculation of the exchange repulsions for minimal QM/MM systems, hydrogen-bonded water dimer, and H3O(+)-H2O. We found that our approach is able to reproduce the potential energy curves for these systems showing reasonable agreements with those given by accurate full quantum chemical calculations.
我们开发了一种简单的方法，用于在量子力学/分子力学（QM/MM）方法中计算量子力学（QM）溶质与分子力学（MM）分子之间的交换排斥力。在我们的方法中，QM溶质的Buckingham型势中的尺寸参数直接根据溶质的单电子波函数确定。该方法的关键在于引入了交换核心函数（ECF），它被定义为一个Slater函数，用于模拟QM/MM边界区域外部电子密度的行为。在本文中，ECF是根据Becke-Roussel（BR）交换空穴函数构建的。结果表明，BR方法产生的ECF能够如实地再现QM溶质电子密度的径向行为。然后，使用重叠模型无需任何拟合过程即可获得溶质的尺寸参数以及交换排斥力。为了检验该方法的效率，将其应用于最小QM/MM系统、氢键水二聚体和H3O(+)-H2O的交换排斥力计算。我们发现，我们的方法能够再现这些系统的势能曲线，与精确的全量子化学计算结果显示出合理的一致性。
