Thermal expansion, diffusion and melting of Li2O using a compact forcefield derived from ab initio molecular dynamics

This work shows a straightforward procedure to derive forcefields (FFs) which are able to describe the structural, thermal and transport properties of condensed phases. The approach is based on ab initio molecular dynamics trajectories and an empirical calibration such as the melting point. This is demonstrated for lithium oxide using a Buckingham-type potential and optimized effective atomic charges. The present FF reproduces the density and thermal expansion of Li2O very well, including an anomaly related to the known superionic behaviour, i.e. a pre-melting of the Li sublattice at a critical temperature of T-c = 1200 K. Calculations of the diffusion coefficient as a function of temperature show a strong dependence on vacancy concentration for temperatures below T-c, consistent with previous simulations. Extensions to other ionic systems and compositions are made straightforward by the compact form of the FF and the present methodology employed in the parameter fitting.