The structure, dynamical and thermodynamic properties of α-Li3N: A first-principles study

We have investigated the structure, dynamical properties and thermodynamic properties of α-Li3N from ab initio density functional theory within local-density approximation (LDA). The results for the lattice constant agree well with available experimental values. A liner response approach to the density functional theory is used to derive the Born effective charge tensors, the dielectric permittivity tensors, the phonon frequencies at the center of the Brillouin zone, the phonon dispersion curves and the corresponding density of states of Li3N. The Born effective charge and the dielectric permittivity tensors are diagonal, which are analyzed in detail. The calculated phonon frequencies at the Γ point of the Brillouin zone show good agreement with the experimental values for most vibrational modes. The thermodynamic properties are investigated within the harmonic approximation based on the calculated phonon dispersion relations. The extensive and successful comparisons with experiments demonstrate once more that the method can provide reliable predictions for the temperature dependence of these quantities, such as the Helmholtz free energy FF, the entropy SS, Gibbs free energy GG, and the enthalpy changes of H−H298.15H−H298.15, and the heat capacity in detail.