D, H, and Mu in GaN: Theoretical predictions at finite temperatures

The so-called 'first-principles' theory of defects in semiconductors is very good at predicting many ground state properties of impurities in periodic supercells at T=0K. Even though the total zero-point energy is at best partially taken into account, these calculations generally lead to reliable geometries, energetics, densities, and local vibrational modes. However, in the case of light impurities such as a proton or muon, the contribution of the zero-point energy is large and must be taken into account. In this paper, we discuss the calculation of structures, dynamical matrices, phonon densities of state and vibrational free energy contributions, and apply the results to D, H, and Mu in GaN. The temperature dependence of the free energy difference between various configurations is calculated.