Validating a polarizable model for the glass-forming liquid Ca0.4K0.6(NO3)(1.4) by ab initio calculations

Ab initio calculations have been performed in order to investigate a recent ly proposed polarizable model [M. C. C. Ribeiro, Phys. Rev. B 61, 3297 (200 0)] for molecular dynamics (MD) simulation of the molten salt Ca0.4K0.6(NO3 )(1.4). On the basis of the electronegativity equalization method, polariza tion effects in the MD simulations have been introduced by a fluctuating ch arge (FC) model for the nitrate ion. Partial charges in the nitrate ion are obtained by ab initio calculations at several levels of theory, and compar ed with previously proposed models for MD simulations of nitrate melts. Cha rge fluctuation is achieved in the ab initio calculations by using positive probe charges placed around a nitrate ion. The parameters of the FC model are corroborated by comparison of the ab initio partial charges with the on es obtained directly by the electronegativity equalization method. Simulate d annealing of a cluster including two double-charged cations and two nitra te ions shows that very different structures are obtained depending on whet her the FC model or its nonpolarizable counterpart is considered. Ab initio calculations show that the structure of this cluster is strongly dependent on polarization effects in the nitrate ions. (C) 2000 American Institute o f Physics. [S0021- 9606(00)52235-1].