<i>Ab initio</i> anharmonic thermodynamic properties of cubic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Ca</mml:mi><mml:mi>Si</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> perovskite
Zhen Zhang, Renata M. Wentzcovitch
Abstract
We present an ab initio study of the thermodynamic properties of cubic $\mathrm{Ca}\mathrm{Si}{\mathrm{O}}_{3}$ perovskite (CaPv) over the pressure and temperature range of the Earth's lower mantle. We compute the anharmonic phonon dispersions throughout the Brillouin zone by utilizing the phonon quasiparticle approach, which characterizes the intrinsic temperature dependence of phonon frequencies and, in principle, captures full anharmonicity. Such temperature-dependent phonon dispersions are used to calculate ab initio free energy in the thermodynamic limit ($N\ensuremath{\rightarrow}\ensuremath{\infty}$) within the framework of the phonon gas model. Accurate free energy calculations enable us to investigate cubic CaPv's thermodynamic properties, e.g., thermal expansivity, Gr\"uneisen parameter, bulk modulus, heat capacity and thermal equation of state, where anharmonic effects are demonstrated. The present methodology provides an important theoretical approach for exploring phase boundaries, thermodynamic, and thermoelastic properties of strongly anharmonic materials at high pressures and temperatures.