Structure factors and x-ray diffraction intensities in molten alkali halides

Abstract

We show by extensive molecular dynamics simulations that rather accurate predictions of structure factors and x-ray diffraction intensities of molten alkali halides can be achieved in terms of the Born-Huggins-Mayer-Fumi-Tosi rigid ion potential description of these systems. Specifically, the partial structure factors of six ionic melts, namely NaCl, RbCl, LiCl, LiF, NaF and KF, are computed by Fourier inversion of the radial distribution functions obtained from simulation; the x-ray diffraction intensity is then obtained from the calculated partial structure factors. We perform a comparison between the molecular dynamics results and the experimental data obtained via neutron and/or x-ray diffraction. We also determine the total number density and total charge structure factors and document that, in all the salts examined, the peaks in the x-ray intensities fall at wavevectors practically coincident with those of the partial and total structure factors. We then show how to improve upon some limits emerging in the adopted model when applied to molten fluorides. We finally comment on the opportunity to extend to other molten alkali halides, for which experimental x-ray diffraction intensities are available, the assessment of structural predictions according to the scheme outlined here.