LITHIUM-OXIDE AND SUPERIONIC BEHAVIOR - A STUDY USING POTENTIALS FROMPERIODIC AB-INITIO CALCULATIONS

A simple general methodology for obtaining interionic potentials from periodic ab initio calculations is presented, using periodic Hartree-F ock theory as implemented in the program CRYSTAL. TO test the approach , two-body potentials are generated for Li2O. Results obtained from ou r new potential are compared with those from previously suggested empi rical potentials, paying most attention to the possibility of superion ic 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 superi onic transition in lithium oxide at 1100 K. Details of the mechanism o f the transition are discussed with the aid of the calculated dispersi on curves at high temperature, and individual molecular dynamics traje ctories. (C) 1997 Elsevier Science Ltd.