Abstract
We have performed first principles molecular dynamics simulations of CaO and CaSiO (sub 3) liquids overbroad ranges of pressure (0 to 150 GPa) and temperature (2500 to 8000 K) within density functional theory. They show that both liquids are much more compressible than their solid counterpart simplyfying possible liquid-solid density crossover. The liquid Gruneisen parameter increases on pressure, which is opposite of crystalline phases. Our analysis shows that the liquid structure changes considerably on compression, with the mean cation-anion coordination numbers increasing nearly linearly with volume. The Ca-O coordination number increases from 7 (5) near the ambient pressure to 9 (7) at high pressure for CaSiO (sub 3) (CaO) liquid. The Si-O coordination number increases from 4 to 6 over the same pressure regime. The calculated self-diffusion coefficients are strongly dependent on temperature and pressure and require non-Arrhenian representation with variable activation volume. The diffusivity differences between the two liquids are considerable in low-temperature and low-pressure regime. Also, comparisons with MgSiO (sub 3) liquid suggest that network modifier cations Ca and Mg behave similarly though Ca is more coordinated and more mobile as compared with Mg.