Laboratory of Physical Chemistry, ETH Zürich, CH-8093 Zürich, Switzerland.
J Chem Phys. 2011 Apr 14;134(14):144103. doi: 10.1063/1.3567020.
The raw single-ion solvation free energies computed from atomistic (explicit-solvent) simulations are extremely sensitive to the boundary conditions (finite or periodic system, system or box size) and treatment of electrostatic interactions (Coulombic, lattice-sum, or cutoff-based) used during these simulations. However, as shown by Kastenholz and Hünenberger [J. Chem. Phys. 124, 224501 (2006)], correction terms can be derived for the effects of: (A) an incorrect solvent polarization around the ion and an incomplete or/and inexact interaction of the ion with the polarized solvent 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 polarized air-liquid interface or of a constraint of vanishing average electrostatic potential in the simulated system; and (D) an inaccurate dielectric permittivity of the employed solvent model. Comparison with standard experimental data also requires the inclusion of appropriate cavity-formation and standard-state correction terms. In the present study, this correction scheme is extended by: (i) providing simple approximate analytical expressions (empirically-fitted) for the correction terms that were evaluated numerically in the above scheme (continuum-electrostatics calculations); (ii) providing correction terms for derivative thermodynamic single-ion solvation properties (and corresponding partial molar variables in solution), namely, the enthalpy, entropy, isobaric heat capacity, volume, isothermal compressibility, and isobaric expansivity (including appropriate standard-state correction terms). The ability of the correction scheme to produce methodology-independent single-ion solvation free energies based on atomistic simulations is tested in the case of Na(+) hydration, and the nature and magnitude of the correction terms for derivative thermodynamic properties is assessed numerically.
从原子（显式溶剂）模拟计算得到的原始单离子溶剂化自由能对边界条件（有限或周期性系统、系统或盒子大小）和模拟过程中静电相互作用的处理（库仑、格子求和或基于截止值）非常敏感。然而，正如 Kastenholz 和 Hünenberger [J. Chem. Phys. 124, 224501 (2006)] 所示，可以推导出校正项来修正以下影响：（A）由于使用近似（不完全库仑）静电方案，离子周围溶剂的极化不正确以及离子与极化溶剂的不完全或/和不精确相互作用；（B）模拟系统的有限尺寸或人为周期性；（C）评估离子位置处势能的不合适求和方案，以及模拟系统中可能存在极化气液界面或平均静电势为零的约束；（D）所使用溶剂模型的介电常数不准确。与标准实验数据进行比较还需要包括适当的空腔形成和标准状态校正项。在本研究中，通过以下方式扩展了该校正方案：（i）为上述方案（连续静电计算）中数值评估的校正项提供简单的近似解析表达式（经验拟合）；（ii）为衍生热力学单离子溶剂化性质（以及溶液中的相应偏摩尔变量）提供校正项，即焓、熵、等压热容、体积、等温压缩系数和等压膨胀系数（包括适当的标准状态校正项）。校正方案在 Na(+) 水合的情况下被测试为基于原子模拟生成方法独立的单离子溶剂化自由能的能力，并通过数值评估评估了衍生热力学性质校正项的性质和大小。
