First-principles study on the high-pressure physical properties of orthocarbonate Ca 2 CO 4

Abstract

AbstractOrthorhombic Ca2CO4(space groupPnma) is a recently discovered orthocarbonate whose high-pressure physical properties are critical for understanding the deep carbon cycle. Here, we study the structure, elastic and seismic properties of Ca2CO4-Pnmaat 20–140 GPa using first-principles calculations, and compare them with the results of CaCO3polymorphs. The results show that the structural parameters of Ca2CO4-Pnmaare in good agreement with the experimental results. It is the potential host of carbon in the Earth's mantle subduction slab, and its low wave velocity and small anisotropy may be the reason why it cannot be detected in seismic observation. The thermodynamic properties of Ca2CO4-Pnmaat high temperature and high pressure are obtained using the quasi-harmonic approximation method. This study provides new insights into the behavior of carbonate and carbon cycles in the mantle.