Structural and dynamical investigation of Mg2SiO4 liquid

Abstract

We have numerically studied structure and dynamics in Mg2SiO4 liquid. Eight models at pressure up to 40 GPa and at a temperature of 3500 K have been constructed by molecular dynamics simulation. The structural characteristics such as short-, intermediate-range order (denoted as SRO, IRO, respectively) structure and network structure are analyzed via the radial distribution functions, coordination units, bond angle, bond length as well as the number of corner-, edge- and face-sharing bonds and characteristics of all type OTy linkages. To clarify the dynamical properties, the models at different pressures are relaxed in NVE ensemble for a long time. The diffusivity of the individual atomic species is determined through the dependence of the mean-squared displacement on number of MD steps. Under compression, the local environment around Si and Mg atoms as well as the IRO structure in Mg2SiO4 changes significantly. The degree of polymerization of the Si–O network increases with pressure. The Si–O bonds are broken; the Mg atoms tend to incorporate into the Si–O network via both bridging oxygen (BO) and non-bridging oxygen (NBO) to form the –Si–O–Mg– network in Mg2SiO4 liquid. In the considered pressure range, the Mg atom always diffuses faster than the O atom and the O atom diffuses faster than the Si atom. The diffusivity of Si, Mg and O atom decreases with increase in pressure.