TECHNICAL REPORT 019 "Theoretical Assesment of Phases of MgO from DFT and MD Simulations"

We use rst principles methods (no empirical parameters) to establish the phase diagram for the B1(NaCl), B2(CsCl), and liquid phases of MgO. We used density functional theory (DFT) with the generalized gradient approximation (GGA) to predict the equation-of-state [volume versus pressure (V (P ))] at 0 K for MgO in the low density B1 (NaCl) phase and the high density B2 (CsCl) phase. We nd a pressure induced phase transition at P = 400GPa. We then tted an MS-Q type force eld (FF) to the quantum results. This FF, denoted as qMS-Q FF, was then used in molecular dynamics (MD) simulations to investigate the phase coexistence curves of the B1-B2 and B1-liquid phases. This leads to a rst-principles phase diagram for MgO for pressures up to 500GPa and temperatures up to 8000K. The accuracy of the t of the qMS-Q FF to the QM validates the functional form of the qMS-Q FF in which the charges are obtained from charge equilibration (QEq) and the nonelectrostatic forces are described with simple two-body Morse potentials. Such qMS-Q FF using no empirical data should be useful for MD or Monte Carlo simulations of many other materials. 64.30.+t, 64.70.Kb, 64.70.Dv, 64.90.+b