COUPLED DENSITY FUNCTIONAL/MOLECULAR MECHANICS MONTE-CARLO SIMULATIONS OF IONS IN WATER - THE BROMIDE ION

A recently developed NPT Monte Carlo method using density functional theory/molecular mechanics potentials is applied to study ion hydration. Test calculations for Na+ and Cl- are in agreement with experimental and classical simulation results. In the case of Br-, the DFT/MM atom-atom radial distribution function is in better agreement with the experimental bromide-oxygen distance than that obtained in the classical simulation. Both models predict a preferred linear Br-H-O arrangement. Fluctuations of the bromide ion electronic cloud are illustrated through the calculation of the instantaneous dipole moment of the ion.