Kastenholz Mika A, Hünenberger Philippe H
Laboratorium für Physikalische Chemie, ETH Zentrum, CH-8093 Zürich, Switzerland.
J Chem Phys. 2006 Jun 14;124(22):224501. doi: 10.1063/1.2201698.
The raw ionic solvation free energies computed from atomistic (explicit-solvent) simulations are extremely sensitive to the boundary conditions (finite or periodic system, system shape, and size) and treatment of electrostatic interactions (Coulombic, lattice sum, or cutoff based) used during these simulations. In the present article, it is shown that correction terms can be derived for the effect of (A) an incorrect solvent polarization around the ion due to the use of an approximate (not strictly Coulombic) electrostatic scheme; (B) the finite size or artificial periodicity of the simulated system; (C) an improper summation scheme to evaluate the potential at the ion site and the possible presence of a liquid-vacuum interface in the simulated system. Taking the hydration free energy of the sodium cation as a test case, it is shown that the raw solvation free energies obtained using seven different types of boundary conditions and electrostatic schemes commonly used in explicit-solvent simulations (for a total of 72 simulations differing in the corresponding simulation parameters) can be corrected so as to obtain a consistent value for this quantity.
从原子级（显式溶剂）模拟计算得到的原始离子溶剂化自由能对边界条件（有限或周期性系统、系统形状和大小）以及这些模拟过程中使用的静电相互作用处理方式（基于库仑、晶格求和或截断）极为敏感。在本文中，结果表明，对于以下几种效应可以推导校正项：(A) 由于使用近似（非严格库仑）静电方案导致离子周围溶剂极化不正确；(B) 模拟系统的有限尺寸或人为周期性；(C) 评估离子位点处势能的不当求和方案以及模拟系统中可能存在的液 - 真空界面。以钠离子的水合自由能作为测试案例，结果表明，使用显式溶剂模拟中常用的七种不同类型边界条件和静电方案获得的原始溶剂化自由能（对应模拟参数不同的总共72次模拟）可以进行校正，从而得到该量的一致值。
