Song-Ho CHONG (Kyoto Univ.) and Fumio HIRATA
[J. Phys. Chem. B 101, 3209 (1997)]
We present a theoretical study for the ion hydration based on an integral equation method referred to as the extended reference interaction site method (ex-RISM). We analyze the thermodynamic functions of solvation, especially the partial molar volumes of individual ions at infinite dilution. A special attention is paid to information contained in the partial molar volumes, and to the problem if the partial molar volumes of individual ions reflect the true nature of ion-water interactions. Our results suggest, on the contrary to the previous work given by Kusalik and Patey, that the partial molar volumes do reflect the nature of ion-water interactions. Concerning the microscopic description of the ion hydration, the earlier model proposed by Samoilov is revisited based on ex-RISM. Characterization due to the integral equation method is found to be in an accord with that proposed by Samoilov. We also discuss the structural changes of water due to the presence of an ion utilizing the density derivatives of the solvent distribution functions. Qualitative difference of the density derivatives between the so-called 'positively hydrated' and 'negatively hydrated' ions was observed and found to be consistent with the analysis of the potential of mean force.