Predicting the energetics of defects at T>0 K

The first-principles theory of defects in semiconductors is very good at predicting most ground state properties of defects in periodic supercells at T=0K. Even though the total zero-point energy is ignored, these calculations lead to reliable geometries, energetics, densities, and local vibrational modes. However, much of the real world operates around room temperature, samples are annealed or exposed to various sources of energy which, ultimately, raise the temperature of the crystal. In this paper, we extend first-principles theory to finite temperatures by calculating explicitly the various contributions to the free energy (at constant volume). The emphasis in this paper is on the temperature and sample dependence of binding free energies.