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.

The relationship between the diffusion coefficient and the viscosity has been examined in computer simulations for a number of ions diffusing in a molten salt (alkali halide) solvent. The comparison gives a measure of a hydrodynamic radius for the diffusing ions which is then compared with the bare ionic radius and a characteristic radius of the coordination complex formed by halide ions around polyvalent cations. K(+) and Cl(-) ions appear to diffuse as isolated spherical particles, whereas the trivalent cations Sc(3+), Y(3+), and La(3+) diffuse as if with an intact coordination shell. These different behaviors can be related to the time scale for the relaxation of the coordination shell, compared to the structural relaxation time of the solvent.