Numerical modelling NaCl solution

Once ions are included in water, it is crucial to employ the dielectrically consistent version of the RISM theory [11, 12]. The basic equations and the algorithm for numerically solving them are described in the Appendix. In the analysis, we choose acetylglycine ethyl ester (AGE) CH3CONHCH2COOCH2CH3 because the salting-out coefficients of this peptide in various salt solutions are experimentally available [53]. Besides, such a peptide serves as one of the basic models of proteins. The conformation is fixed at the all-trans form in our calculations. The SPC/E model is employed for water. The following two sets of salt solutions are considered to examine the effects of cations and anions on the solvation properties of AGE LiCl, NaCl, and KGl (set 1) for the cation effects, and NaCl, NaBr, and Nal (set 2) for the anion effects. The temperature and the salt concentration are fixed at 298K and IM, respectively. The number density and the dielectric constant of each salt solution, which are used as part of the input data in the dielectrically consistent version of the RISM theory, are taken from the experimental data. We adopt the Coulomb plus L-J potential functions for all the interactions between water-solute and ion-solute atomic pairs. That is, the site-site pair potential Uab r) is expressed as Eq.(3.17) (for the NaCl-solution, for example, 6=H,0,Na+,Cl ). The AMBER-type potential parameters are employed for the peptide. 

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