  Within the framework of density functional theory (DFT), the total energy of
crystal structures is calculated at zero temperature. Herein, we briefly
discuss the DFT-based lattice-dynamics approach for computing crystal free
energy, the quantity needed in various non-zero-temperature contexts. We
illustrate this well-established approach by examining the
temperature-dependent thermodynamic stability of several crystalline materials,
including ZrO$_2$, HfO$_2$, KBH$_4$, and Zn(BH$_4$)$_2$.
