Ab initiolattice dynamics and thermodynamics of rare-earth hexaboridesLaB6andCeB6

Abstract

We have performed an ab initio study of structural, elastic, lattice-dynamical, and thermodynamical properties of rare-earth hexaborides ${\text{LaB}}_{6}$ and ${\text{CeB}}_{6}$. The calculations have been carried out within the density-functional theory and linear-response formalism using pseudopotentials and a plane-wave basis. Thermodynamical properties of ${\text{LaB}}_{6}$ and ${\text{CeB}}_{6}$ obtained from quasiharmonic approximation are in a good agreement with the available experimental data. We also present the complete phonon-dispersion curves, phonon density of states, and mode-Gr\"uneisen parameters and compared with the experimental measurements. A sizable difference between the vibrational contribution to entropy of ${\text{LaB}}_{6}$ and ${\text{CeB}}_{6}$ is found. The thermal electronic contribution to entropy and specific heat is found to be important for ${\text{CeB}}_{6}$.