Ion solvation in water from molecular dynamics simulation with the ABEEM/MM force field

A systematic study on monovalent ions in water clusters and in aqueous solution is presented for providing insight into their solvation structures, charge distributions, binding energies, as well as dynamic and thermodynamic properties in terms of the atom-bond electronegativity equalization method fused into molecular mechanics (ABEEM/MM) that is to take ABEEM charges into the Coulomb term in MM. For hydrated systems of M+(H2O)n, M+ being Li+, Na+, and K+, as well as X-(H2O)n, X- being F-, Cl-, and Br-, with n = 1-6, parameters for the effective interaction between the ion and the water molecules were determined, so as to reproduce the experimental or ab initio results. The corresponding parameters were tested with molecular dynamics (MD) simulations of these ions in liquid water and with solvation free energy calculations using the perturbation technique. The results of aqueous ionic solution simulations with the ABEEM/MM force field provide a reasonable description of many important properties, which are in good agreement with the experimental measurements. This work demonstrates that the combination of ABEEM/MM-MD provides a powerful tool in analyzing solvation processes of monovalent ions in water.