Phonon spectrum and thermodynamic properties of LaCoO3 based on first-principles theory

Abstract

The structural, vibrational, phonon dispersion spectrum, and thermodynamic properties of LaCoO3 were investigated using first-principles calculations using density functional theory. Calculations were performed using the projector augmented wave (PAW) pseudopotentials within the generalized-gradient approximation (GGA) and local density approximation (LDA) models for the exchange and correlation functional. In addition, GGA+U and LDA+U were used to describe the 3d electrons. The phonon dispersion spectrum and phonon density of states of LaCoO3 were calculated with the finite displacement method. The related thermodynamic properties such as heat capacity, entropy, free energy, and the coefficient of thermal expansion were calculated at various temperatures from the lattice dynamical data obtained by quasi-harmonic approximation. The phonon dispersion spectrum results indicate that the LaCoO3 structure is dynamically stable. The phonon dispersion and the peaks of the infrared (IR) and Raman spectrum in the frequency range of 0–700cm−1 were analyzed and assigned. The calculated thermodynamic properties agree well with the experimental results.