A Local Entropic Signature of Specific Ion Hydration

被引:44
作者
Beck, Thomas L. [1 ,2 ]
机构
[1] Univ Cincinnati, Dept Chem, Cincinnati, OH 45221 USA
[2] Univ Cincinnati, Dept Phys, Cincinnati, OH 45221 USA
基金
美国国家科学基金会;
关键词
INITIO MOLECULAR-DYNAMICS; QUASI-CHEMICAL THEORY; FREE-ENERGY; AB-INITIO; LIQUID WATER; SOLVATION; SIMULATIONS; MECHANICS; FORCES;
D O I
10.1021/jp204883h
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Monovalent ion hydration entropies are analyzed via energetic partitioning of the potential distribution theorem free energy. Extensive molecular dynamics simulations and free energy calculations are performed over a range of temperatures to determine the electrostatic and van der Waals components of the entropy. The far-field electrostatic contribution is negative and small in magnitude, and it does not vary significantly as a function of ion size, consistent with dielectric models. The local electrostatic contribution, however, varies widely as a function of ion size; the sign yields a direct indication of the kosmotropic (strongly hydrated) or chaotropic (weakly hydrated) nature of the ion hydration. The results provide a thermodynamic signature for specific ion effects in hydration and are consistent with experiments that suggest minimal perturbations of water structure outside the first hydration shell. The hydration entropies are also examined in relation to the corresponding entropies for the isoelectronic rare gas pairs; an inverse correlation is observed, as expected from thermodynamic hydration data.
引用
收藏
页码:9776 / 9781
页数:6
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