Structural and dynamical properties of MgSiO3 melt over the pressure range 200–500 GPa: Ab initio molecular dynamics

• GGA overestimates the average length of MgO bonds than LDA.
• The SiO coordination number increases nearly linearly from 6.4 to 7.3.
• Oxygen tricluster is formed over pressure range from 230.1 to 464.7 GPa at 13,000 K.
• The shear viscosity increases from about 4 to10 cP over pressure range 200–500 GPa.

Ab initio molecular dynamics simulations on MgSiO3 melt have been performed over the pressure range 200–500 GPa. The results calculated by local density approximation (LDA) and generalized gradient approximation (GGA) were compared. Our results showed that compared with experimental data, LDA can yield more accurate pressure and thus the thermal equation of state and Hugoniot curve than GGA. The reason is that in MgSiO3 melt GGA overestimates the average length of MgO bonds than LDA, while they yield nearly the same results for SiO and OO bonds. Over the pressure range 230.1–464.7 GPa at 13,000 K, the calculated pair correlation function changes gradually, the mean SiO coordination number increases nearly linearly from 6.4 to 7.3 while the MgO and OO coordination numbers are almost unchanged, indicating no signature of a first-order liquid–liquid phase transition. The calculated distribution of OSi coordination number presents evidence for the presence of oxygen triclusters (oxygen coordinated with three Si frameworks). The calculated diffusion coefficient decreases from about 4 to 2 × 10− 4 cm2/s but the shear viscosity estimated using Zwanzig's formula increases from about 4 to 10 cP with increasing pressure from 230.1 to 464.7 GPa at 13,000 K.