Periodic Hartree-Fock study of B1 ⇌ B2 reactions: phase transition in CaO

Abstract The periodic Hartree-Fock method has been used to sample the potential energy hypersurface of CaO to determine a collective reaction pathway between the low-pressure (NaCl) and high-pressure (CsCl) phases. The predicted transition pressure, 68 GPa, is in good agreement with both experimental data and previous theoretical studies. At low pressure the enthalpy ( E + PV ) surface presents only one minimum corresponding to the B 1 (NaCl) structure. A second minimum appears at the B 2 (CsCl) geometry when the pressure is increased. The transformation kinetics is estimated using the Johnson-Mehl model coupled to random nucleation and interface-controlled growth. Independently of the interfacial energy, the kinetics is highly pressure dependent. A pressure hysteresis loop is predicted. The results presented are in qualitative agreement with available data.