A First-Principles Description of Liquid BeF₂ and Its Mixtures with LiF:  1. Potential Development and Pure BeF₂

Abstract

The construction of an interaction potential for BeF2 and its mixtures with LiF on a purely first-principles basis is described. The quality of the representation of the forces on the ions obtained from ab initio electronic structure calculations by various potentials, which include many-body interaction effects to different extents, are considered. The predictions of the properties of pure BeF2 obtained in simulations with a polarizable potential are then compared with experimental values. In the subsequent paper, a more extensive comparison of the predicted properties of LiF-BeF2 mixtures with experiment is considered.

Including many-body effects in models for ionic liquids

“…88,89 For this reason, it was the ideal testing ground for evaluating our interaction potential development approach and we focused first on this system. 37 We could show that our model performed very well in reproducing the polymeric fluoroberyllate speciation and the vibrational properties in these melts. 87 Calculated dynamic properties (electrical conductivity, viscosity) also agree quantitatively with the experimental data: 90 To illustrate this, we show a comparison of the calculated 87 and experimental 88 viscosities of LiF-BeF 2 mixtures with varying compositions at T = 873 K on figure 5.…”

Fluctuating ionic polarizabilities in the condensed phase: first-principles calculations of the Raman spectra of ionic melts

“…The Raman spectrum of liquid BeF 2 was calculated at 1300 K. The simulations were carried out with both quadrupole and dipole polarizable interaction potentials 39 , with similar results obtained in both cases.…”

“…Firstly, we create several sets of ionic configurations for the materials of interest. They are generated by molecular dynamics simulations using high quality interaction potentials obtained by ab initio force-fitting as described previously 31,32,39 .…”

“…Using a quadrupole-polarizable interaction potential 39 we carried out an equivalent parameterization of the light scattering model for liquid BeF 2 . DFT calculations of the ionic polarizabilities were performed on three liquid configurations, each containing 72 ions, which were taken from simulations of the liquid phase at 1300 K. The F − ion polarizabilityᾱ F extracted from these calculations are smaller than those seen in This is consistent with a short-range effect of comparable magnitude, but which decays more rapidly with ionic separation due to the smaller size of the Be 2+ ion.…”

“…Alongside cryolite 5,24 , the electrolyte involved in aluminium extraction, it is by far the best-characterized fluoride melt. We have already determined interaction potentials for these mixtures and compared simulation results with a wide range of observable properties 32,39,40 in the liquid and solid state.…”