The lattice dynamics of α- and γ-Ce: a first-principles approach

Abstract

An Ab initio pseudopotentials plane wave method supplemented with the linear responseapproach has been employed to study the lattice dynamics of face-centered cubic (fcc)α- andγ-cerium. The bulk properties, entire phonon dispersions, phonon densityof states, and temperature-dependent thermodynamic quantities of bothcerium phases are obtained. With regard to the phonon spectrum ofα-Ce, it exhibits imaginary phonon frequencies near theΓ point, indicating that this phase is unstable under low ambientpressure. The calculated phonon spectrum and elastic constants ofγ-Ce successfully reproduce several extraordinary features, including pronouncedphonon softening at the L point, particularly low energy phonons along theT[ξξξ] branch, and large elastic anisotropy. Some apparent discrepancieshave been observed between the phonon density of states ofα- andγ-Ce. As a result, the phonon entropy change across theα–γ phase boundary is not negligible. To obtain a full understanding of the driving force of the fascinatingα–γ phase transition, the lattice contribution should be taken into consideration.