From ab-initio thermodynamics to quasi-harmonic thermoelastic properties of crystals: A new workflow and selected applications

In this thesis we investigate several thermodynamic properties of materials from ab-inito calculations and the quasi-harmonic approximation (QHA) by means of the thermo_pw code. We present its general scheme of operation, extending the calculation to the temperature dependent elastic constants (ECs). The calculation can be done within either the quasi-static or the QHA and can provide both the isothermal and isoentropic ECs. We apply our method to several metals (Al, Ag, Au, Cu, Pd, and Pt) and semiconductors (Si and BAs). The results are compared with the available experimental data. The effect of finite temperature electronic excitation as well as of the exchange and correlation functional are discussed. We also address the effect of finite-temperature atomic relaxations and their contributions to the ECs of Si and BAs. Finally, we leave the discussion about ECs to present the implementation of the temperature-dependent atomic B-factor.