Development of first-principles interaction model potentials.: An application to the study of the bromide hydration

This work presents the development of first-principles bromide ion-water interaction potentials using the mobile charge density in harmonic oscillators-type model. This model allows for a flexible and polarizable character of the interacting molecules and has already been parametrized for water-water interactions. The prospected potential energy surfaces of the bromide ion-water system were computed quantum-mechanically at Hartree-Fock and Moller-Plesset second-order perturbation levels. In addition to the ion-solvent molecule pair, structures formed by the anion and two or three water molecules were considered in order to include many body effects. Minimizations of hydrated bromide clusters in gas phase [Br(H2O)(n)](-) (n=1-6,10,15,20) and Monte Carlo computations of bromide aqueous solutions were performed to test the new potentials. Both structural and thermodynamic properties have been studied in detail and compared to the available experimental and theoretical values. From these comparisons, it was concluded the importance of including basis set superposition error corrections for the two-body interactions, and the small role of both electron correlation on the three-body terms and the four-body terms. Monte Carlo simulation results have also been used to investigate if the presence of the anion significantly affects the intramolecular geometry of the water molecules and the degree of disruption of the water solvent structure in its vicinity.(C) 2002 American Institute of Physics.