Kalcher Immanuel, Dzubiella Joachim
Department of Physics T37, Technical University Munich, 85748 Garching, Germany.
J Chem Phys. 2009 Apr 7;130(13):134507. doi: 10.1063/1.3097530.
The structure of aqueous LiCl, NaCl, KCl, CsCl, KF, and NaI solutions is calculated by molecular dynamics (MD) simulations of the frequently employed Dang force-field in SPC/E water. By using liquid state theory, we integrate the structure to obtain the electrolytes' osmotic coefficient phi and systematically investigate force-field quality and structural consequences to ion-specific bulk thermodynamics. The osmotic coefficients phi(chi) calculated from the exact compressibility route for the cation-Cl(-) force-fields match experiments for concentrations rho approximately < 2M, while NaI and KF parameters fail. Comparison of phi(chi) with phi(v) from the virial route, which relies on the pair potential approximation, shows that many-body effects become important for all salts above rho approximately 0.5M. They can be efficiently corrected, however, by employing a salt-type and rho-dependent dielectric constant epsilon(rho), generalizing previous observations on NaCl only. For physiological concentrations, rho approximately < 0.5M, the specific osmotic behavior is found to be determined by the short-ranged cation-anion pair potential only and is strongly related to the second virial coefficient of the latter. Presented methods and findings, based on simple integrations over the electrolyte structure, enable efficient MD force-field refinement by direct benchmarking to the sensitive electrolyte thermodynamics, instead to noncollective, single ion properties.
通过在SPC/E水中使用常用的Dang力场进行分子动力学（MD）模拟，计算了LiCl、NaCl、KCl、CsCl、KF和NaI水溶液的结构。利用液态理论，我们对结构进行积分以获得电解质的渗透系数φ，并系统地研究力场质量和离子特异性体相热力学的结构后果。对于阳离子-Cl⁻力场，从精确压缩性途径计算得到的渗透系数φ(χ)与浓度ρ约<2M时的实验结果相符，而NaI和KF的参数则不相符。将φ(χ)与依赖于对势近似的维里途径得到的φ(v)进行比较，结果表明，对于所有ρ约>0.5M的盐，多体效应变得很重要。然而，通过采用盐类型和ρ依赖的介电常数ε(ρ)，可以有效地校正这些效应，这是对之前仅关于NaCl的观察结果的推广。对于生理浓度ρ约<0.5M，发现特定的渗透行为仅由短程阳离子-阴离子对势决定，并且与后者的第二维里系数密切相关。基于对电解质结构的简单积分所提出的方法和发现，能够通过直接与敏感的电解质热力学进行基准测试来有效地改进MD力场，而不是与非集体的单离子性质进行比较。
