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Calculating heat of formation using DFT: Some guidelines for the study of TCP phases
- Date: 23.05.2011
- Place: XL CALPHAD, Computer Coupling of Phase Diagrams and Thermochemistry, Rio de Janeiro, Brazil
Calculating heat of formation using first-principles density theory (DFT) has been in common usage for several decades, in particular to support the Calphad method. In fact, Calphad thermodynamic modeling requires a complete energetic description of a system, which could be limited by experimental works alone. To compensate for the lack of information, DFT calculations can provide formation enthalpies at 0K of any ordered compounds, even in metastable or non-stable states.
The aim of this work is to present our experience of DFT calculations to estimate the heat of formation of compounds formed at 0K, with a focus on the complex topologically-close packed phases (TCP). Taking the chi and sigma phases as examples, we present calculations of all ordered configurations for several rhenium-based systems. For each of the above systems, we discuss the influence on the converged energy of one specific parameter per DFT calculation: (i) of the basic pseudo-potential parameters, (ii) of the exchange-correlation functional LDA and GGA (PW91 or PBE), (iv) of the magnetic contribution, and (v) of the number of valence electrons considered with different pseudo-potentials.
For each of the above points, we pay attention to the validity of ab initio results in comparison with experimental data available: lattice parameters, internal coordinates, site occupancies and enthalpies of formation.