Classical simulations with the POLIR potential describe the vibrational spectroscopy and energetics of hydration: divalent cations, from solvation to coordination complex.

POLIR, a polarizable water potential optimized for vibrational and intermolecular spectroscopy in pure water but not optimized for solvation, is used to describe solutions of the divalent metal cations Ca(2+), Mg(2+), and Cu(2+). The spectral shifts in the O-H stretch region obtained from classical simulations are in agreement with experiment. The water-ion binding energies are dominated by classical electrostatics, even though the Cu(2+) case might be considered to involve an intermediate-strength chemical bond. Three-body energies of the ion with the first solvation shell are in agreement with ab initio calculations. Our results indicate the importance of polarization in the development of accurate, transferable, force fields and the power of classical methods when it is carefully included.