Molecular Dynamics Simulation of Silica with a First- Principles Interatomic Potential SHINJI TSUNEYUKI Institute for Solid State Physics, University of Tokyo Roppongi, Minato-kzl, Tokyo 106, Japan Key words. Ab initio pair potentials, Molecular dynamics, silical, quartz, cristobalite, liquid silica, phase transitions 1. Introduction Prediction of the structures and properties of materials from a knowl- edge of their chemical composition has been a longstanding problem of materials science. The Molecular Dynamics method (MD, hereafter) has been one of the most powerful techniques to simulate both static and dy- namical properties of materials starting from atomistic information, i.e. an interatomic potential, which we expect not to be affected by a small change in environment of the atoms. In the study of silica and silicates, MD was primarily used to simulate molten and vitreous states using ionic and pairwise interatomic potentials [l, 2, 3, 41, where the interatomic potential was obtained empirically by trial and error. Although the fourfold oxygen coordination of silicon atoms and non-linear Si-0-Si angle widely observed in silica and silicates seem to suggest covalent character of the Si-0 bonds, it has been shown that these structural properties are roughly reproduced by pairwise interatomic potentials. When the application was extended to simulation of crystalline silica and silicate, however, we encounter the fact that these interatomic poten- tials does not necessarily reproduce important structural properties such as bulk moduli, elastic constants or sometimes even dynamical stability of the crystalline symmetry. Thus some efforts have been made to incorporate crystal structures and their elastic properties into the process of empirical determination of the interatomic potentials by means of a static energy minimization technique [5, 6, 7, 8, 91. Molecular Engineering 6: 157-182, 1996. 0 1996 Kluwer Academic Publishers. Printed in the Netherlands.