Molecular dynamics simulation of concentrated lithium-liquid ammonia solutions using a pseudopotential

Abstract

Molecular dynamics simulations of a concentrated lithium-liquid ammonia solution have been performed at an average temperature of 241 K. The basic cube contains 50 Li+,50 delocalized electrons and 205 NH3 (19.58 mole percent of lithium ions). With an experimental density of 0.498 g.cm-3, a side-length of a periodic cube of 23.39 Aํ was obtained. Interactions between particles in the simulation cube were described by the direct and indirect potentials. The first function was developed using quantum chemical calculations while the second one, which represents the effect of free electrons dissolved in the solution, was evaluated based on pseudopotential theory. Two pseudopotential models were employed in this study. The results show that the lithium ion was solvated by six ammonia molecules. The solvent structure was completely changed in comparison with that observed for pure liquid ammonia. Big clusters of Lim(NH3)n+ sharing of one ammonia molecule by2, 3 and 4 lithium ions have been detected. As a consequence of the cluster formation big cavities are formed in the solution