Molecular dynamics study of the structural and thermodynamic properties of MgO crystal with quantum correction

Abstract

We have applied the constant temperature and pressure molecular dynamics technique to the simulation of structural and thermodynamic properties of the MgO crystal in the temperature range between 300 and 2000 K, using empirical pair potential functions consisted of the Coulomb, dispersion, and repulsion interactions. Quantum corrections are included, based on the Wigner–Kirkwood expansion of the free energy in powers of Planck constant h. In the present study, only the first nonvanishing term with the order h2 is considered. As expected, quantum effects on the properties are found to become increasingly important with decreasing temperature. In view of the simplicity of the potential used, our simulation is quite successful in reproducing a wide range of measured properties of MgO, including the crystal structure, bulk modulus, thermal expansion coefficient, heat capacity, and mean-square atomic displacements over a wide temperature range above 500 K. However, at lower temperatures, both the heat capacity and thermal expansion coefficient of MgO are computed to decrease too sharply with decreasing temperature when compared with experiment. This indicates the necessity of including higher-order quantum correction terms at low temperatures for a more accurate description.