First-principles study of the thermodynamical, structural, transport properties of liquid CaO and CaSiO3 at high pressure

Abstract:

We have performed first principles molecular dynamics simulations of CaO and CaSiO3 liquids over
broad 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 counterparts
implying possible liquid-solid density crossover. The liquid Grüneisen 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 CaSiO3 (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 MgSiO3 liquid suggest that network
modifier cations Ca and Mg behave similarly though Ca is more coordinated and more mobile as
compared with Mg.