Department of Chemistry, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
J Chem Phys. 2010 Jan 28;132(4):044106. doi: 10.1063/1.3298873.
We first describe a wave-function based formalism of polarizable charge model by starting from the Hartree product ansatz for the total wave function and making the second-order expansion of individual molecular energies with the use of partial charge operators. The resulting model is shown to be formally equivalent to the charge response kernel model that starts from the linear-response approximation to partial charges, and also closely related to a family of fluctuating charge models that are based on the electronegativity equalization principle. We then apply the above model to a systematic comparison of polarization effects on qualitatively different liquids, namely, protic solvents (water and methanol), an aprotic polar solvent (acetonitrile), and imidazolium-based ionic liquids. Electronic polarization is known to decelerate molecular motions in conventional solvents while it accelerates them in ionic liquids. To obtain more insights into these phenomena, we consider an effective decomposition of total polarization energy into molecular contributions, and show that their statistical distribution is well-correlated with the acceleration/deceleration of molecular motions. In addition, we perform effective nonpolarizable simulations based on mean polarized charges, and compare them with fully polarizable simulations. The result shows that the former can reproduce structural properties of conventional solvents rather accurately, while they fail qualitatively to reproduce acceleration of molecular motions in ionic liquids.
我们首先从总波函数的哈特利积假设出发，通过使用部分电荷算符对单个分子能量进行二阶展开，从而描述了基于波函数的极化电荷模型的形式。所得到的模型在形式上与从部分电荷的线性响应近似出发的电荷响应核模型等效，并且与基于电负性均衡原理的一系列变化电荷模型密切相关。然后，我们将上述模型应用于对定性不同的液体（即质子溶剂（水和甲醇）、非质子极性溶剂（乙腈）和咪唑鎓基离子液体）的极化效应进行系统比较。众所周知，电子极化会减缓传统溶剂中的分子运动，而会加速离子液体中的分子运动。为了更深入地了解这些现象，我们考虑将总极化能有效分解为分子贡献，并表明它们的统计分布与分子运动的加速/减速密切相关。此外，我们基于平均极化电荷执行有效的非极化模拟，并将其与完全极化模拟进行比较。结果表明，前者可以相当准确地再现传统溶剂的结构特性，而在离子液体中分子运动的加速方面则无法定性再现。
