Development of a Transferable Variable Charge Potential for the Study of Energy Conversion Materials FeF2 and FeF3

A variable charge potential is developed that is suitable for the simulations of energy conversion materials FeF 2 and FeF 3 . Molecular dynamics simulations using this potential show that the calculated structural and elastic properties of both FeF 2 and FeF 3 are in good agreement with experimental data. Such a transferability of this potential rests in the fact that the difference in the bond characteristic between FeF 2 and FeF 3 is properly accounted for by the variable charge approach. The calculated equilibrium charges are also in excellent agreement with first-principles Bader charges. Surface energies obtained by the variable charge method are closer to the first-principles data than are fixed charge models, indicating the importance of variable charge method for the simulations of the surface. A significant decrease in atomic charges is observed only for the outermost one or two layers, which is also observed in the first-principles calculations.