非极化力场中电子极化的计算
Accounting for electronic polarization in nonpolarizable force fields
摘要：
讨论了分子动力学模拟中的电子极化率问题。我们认为，蛋白质中电离基团的电荷，以及离子在传统的非极化力场如CHARMM，AMBER，GROMOS等中的电荷应按约0.7的因子缩放。我们的模型解释了为什么忽略电子溶剂化能，这通常相当于总溶剂化能的一半，在非极化模拟与未缩放的电荷可以产生正确的结果;然而，正确的离子溶剂化能并不能保证正确的离子对相互作用在许多非极化模拟。包括带电部分的电子屏蔽显示，导致蛋白质动力学的显着变化，并可以产生新的定性结果相比，传统的非极化力场模拟。该模型还解释了最近从头计算和实验研究中报道的水偶极子$μ$ ~3D与经验势（如TIP 3 P或SPC/E）中通常使用的值$μ_{eff}$ ~2.3D之间的显著差异。水的有效偶极子可以理解为一个比例值$μ_{eff}=μ/\sqrt{ε_{el}}$，其中$ε_{el}$ =1.78是水的电子（高频）介电常数。这个简单的理论框架提供了重要的见解的有效参数的性质，这是至关重要的，当液态水的计算模型用于模拟在不同的环境中，如蛋白质，或与溶质的相互作用。
英文摘要：
The issues of electronic polarizability in molecular dynamics simulations are discussed. We argue that the charges of ionized groups in proteins, and charges of ions in conventional non-polarizable force fields such as CHARMM, AMBER, GROMOS, etc should be scaled by a factor about 0.7. Our model explains why a neglect of electronic solvation energy, which typically amounts to about a half of total solvation energy, in non-polarizable simulations with un-scaled charges can produce a correct result; however, the correct solvation energy of ions does not guarantee the correctness of ion-ion pair interactions in many non-polarizable simulations. The inclusion of electronic screening for charged moieties is shown to result in significant changes in protein dynamics and can give rise to new qualitative results compared with the traditional non-polarizable force field simulations. The model also explains the striking difference between the value of water dipole $μ$~3D reported in recent ab initio and experimental studies with the value $μ_{eff}$~2.3D typically used in the empirical potentials, such as TIP3P or SPC/E. It is shown that the effective dipole of water can be understood as a scaled value $μ_{eff}=μ/\sqrt{ε_{el}}$, where $ε_{el}$=1.78 is the electronic (high-frequency) dielectric constant of water. This simple theoretical framework provides important insights into the nature of the effective parameters, which is crucial when the computational models of liquid water are used for simulations in different environments, such as proteins, or for interaction with solutes.
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