Phase diagram calculations in the Co–Mo and Fe–Mo systems using first-principles results for the sigma phase

We calculate the phase diagrams of Co–Mo and Fe–Mo systems by means of a combination of ab initio electronic structure calculations and the CALPHAD approach. Ab initio calculations of the total energy differences between the sigma phase and standard element reference (SER) structures for pure constituents are accomplished by means of the full-potential linearized augmented plane wave (FLAPW) method in the generalized gradient approximation (GGA). During these calculations the structure relaxation is performed. The results obtained are employed as a part of the Gibbs energy describing the thermodynamics of the sigma phase. Subsequently, the thermodynamic data sets describing the sigma phases in the Co–Mo and Fe–Mo systems are optimized using the CALPHAD approach by employing both the experimental and thermodynamic data extended by ab initio calculations. Description of all other phases is taken from the literature.