Lithium oxide and superionic behaviour - a study using potentials from periodic ab initio calculations

A simple general methodology for obtaining interionic potentials from periodic ab initio calculations is presented, using periodic Hartree-Fock theory as implemented in the program CRYSTAL. TO test the approach, two-body potentials are generated for Li2O. Results obtained from our new potential are compared with those from previously suggested empirical potentials, paying most attention to the possibility of superionic behaviour in this material at high temperatures. The application of ab initio Hartree-Fock theory, lattice statics, lattice dynamics and molecular dynamics is able to provide a consistent picture of a superionic transition in lithium oxide at 1100 K. Details of the mechanism of the transition are discussed with the aid of the calculated dispersion curves at high temperature, and individual molecular dynamics trajectories. (C) 1997 Elsevier Science Ltd.