Derivation and validation of model potentials for Li2O from density-functional theory

We present a methodology used to generate interatomic potentials fitted on results of ab initio calculations. Our aim is to obtain models suitable for large-scale simulations in ionic solids. We fitted a potential based on the rigid-ion model in order to investigate the high-temperature properties of lithium oxide. Density-functional theory calculations with the local density approximation are performed to obtain ground-state properties, used as fitting quantities. The Car-Parrinello method with pseudopotentials and a plane wave basis is used to minimize the total energy. Calculations concerning the elastic moduli have been performed and give results in good agreement with experimental values. The ab initio data selected for the fitting procedure involved pressure and energy differences calculated for various configurations. The ionic charges used in the model are the nominal ones. The fitted parameters only concern short-range interactions. Five potentials have been fitted, they differ by the number of parameters or by the choice of the fitting quantities. The validation of this model potential includes the calculation of the expansion coefficient, the formation energy of the cationic Frenkel defect, the elastic moduli and the temperature evolution of the heat capacity, the thermal vibrations and the diffusion coefficients of lithium ions,