Local Structure of Molten Lithium Fluoride. II. Structure Factor Calculation by Ab Initio and Classical Molecular Dynamics Methods

Abstract

The partial structure factors (PSFs) of molten lithium fluoride at a temperature of 1200 K are calculated using the following three methods: ab initio and classical molecular dynamics and the charged hard sphere model in the mean-spherical approximation. Despite the common topology of the PSFs calculated by all three methods, the key feature of the computer simulation results is shown to be the absence of a shoulder on the right side of the first peak of the cation–cation structure factor. The observed difference is assumed to be associated with the softness of the repulsive branch of the Buckingham pair potential in the case of the classical model in the molecular dynamics calculation. The ab initio molecular dynamics calculations also confirm this conclusion. The results of calculating the density–density structure factor by computer simulation methods demonstrate the presence of two maxima at k ≈ 2.4 and ≈4.4 Å^–1, respectively. The charged hard sphere model demonstrates the presence of one maximum at k ≈ 3.5 Å^–1 and a small shoulder on the left, the position of which coincides with the first maximum obtained by computer simulation methods. The observed differences can be attributed to the fact that the cation–anion PSF curve calculated in terms of the charged hard sphere model has a higher amplitude in the vicinity of a wavevector of ≈3.5 Å^–1.