First-principles calculations of phonon and thermodynamic properties of Fe-Si compounds

The phonon approach and the Debye model are combined to predict the vibrational thermodynamic contribution for the following Fe-Si compounds: Fe3Si, Fe2Si, Fe5Si3, FeSi, β-FeSi2 and α-FeSi2. Both the ultrasoft pseudopotential (USPP) and the projector augmented wave (PAW) methods are employed to describe the electron-ion interactions. The generalized gradient approximation including PW91 and PBE is employed to describe the exchange-correlation functional. Lattice parameters, bulk modulus, phonon dispersions, and finite temperature thermodynamic properties are calculated and compared with available experimental data, and good agreement is observed. The thermodynamic data obtained in the present work provide better understanding of the stability of binary Fe-Si compounds and can be used for further thermodynamic modeling of this system.