First-principles lattice dynamics and heat capacity of BiFeO3

We study the lattice dynamics of bismuth ferrite (BiFeO3) rhombohedral ferroelectric (R3c) using first-principles density functional theory calculations and the direct force constant method. We determine the phonon dispersions, phonon density of states, and heat capacity. Special attention is paid to the heat capacity at low temperature, at which the present phonon calculations show significant deviations from the Debye-like T3 behavior until T ⩽ 7 K. Based on the excellent agreement between the measured and calculated curve shapes of the heat capacity we propose that no gapped magnon modes exist for BiFeO3 that contribute to the heat capacity of BiFeO3 in the temperature range 5–30 K.