Mp2 solvation free energy of simple ions obtained through force matching to simple pairwise potentials

by Li, Jicun; Wang, Feng

Simple non-polarizable potentials were developed for Li+, Na+, K+, F-, Cl-, and Br- using the adaptive force matching method with ab initio MP2 method as ref. Our MP2-AFM force field predicts the solvation free energies of the nine salts formed by the ions with an error of no more than 2%. Other properties, such as the ion-water radial distribution functions, first solvation shell water tilt angle distributions, ion diffusion consts., concn. dependent surface tension of the solns. were calcd. with this potential. Very good agreement was achieved for these properties. In particular, the diffusion consts. of the ions are within 6% of exptl. measurements. Although the potential provides satisfactory prediction for the concn. dependent surface tension, the model predicts all the ions to be repelled from the top-most layer of the liq.-vapor interface, which may be a limitation of the implicit treatment of polarization effect.