Temperature and pressure effects on phase stabilities in the Ca–Ge system from first-principles calculations and Debye-Gruneisen model

We present a study of phase stabilities of intermetallics in the Ca–Ge system including finite temperature and pressure effects based on density functional theory (DFT) within the projector augmented wave (PAW) method. Temperature effects, mainly represented by vibrational degrees of freedom, were taken into account within the Debye-Gruneisen model. The results predict the existence of two new polymorphs of the CaGe2 compound. The pressure-temperature phase diagram of this polymorphism is calculated. The stabilization by both temperature and pressure of a new compound of the Ca3Si4-type is also predicted in this system.