Ab initio quasiharmonic equations of state for dynamically stabilized soft-mode materials

[摘要] We introduce a method for treating soft modes within the analytical framework of the quasiharmonic equation of state. The corresponding double-well energy-displacement relation is fitted to a functional form that is harmonic in both the low- and high-energy limits. Using density-functional calculations and statistical physics, we apply the quasiharmonic methodology to solid periclase (MgO). We predict the existence of a B1-B2 phase transition at high pressures and temperatures.

[关键词] MOLECULAR-DYNAMICS;MGSIO3 PEROVSKITE;LATTICE-DYNAMICS;PHASE-TRANSITIONS;FIRST-PRINCIPLES;MAGNESIUM-OXIDE;LOWER MANTLE;PSEUDOPOTENTIALS;SIMULATIONS;PHONONS