Place: Bundesanstalt für Materialforschung und -prüfung, Berlin, Germany
First-principles calculations based on Density Functional Theory (DFT) can provide the understanding for the physical origin of the different contributions to properties such as the heat capacity, voliumes, formation enthalpies, etc. due to vibrational, electronical and magnetic excitations.
Unsing a methodology that we named SAPIENS, where the advantages of DFT and CALPHAD method are integrated, first-principles and experimental databases for the pure elements are produced and predictive parametric modeling for the pure elements are produced and predictive parametric modeling of thermophysical properties such as bulk modulus and thermal expansion are made available. Our approach is based on the Helmholtz energy for ease of coupling with first-principles calculations. The methodology has been demonstrated for four technologically important pure elements (Fe, Cr, Ni, Al) and will be subsequently extended to more elements.
A new code for unaires, Open Unary (developed by Mauro palumbo), in C++ as part of the Open Caphad software (developed by Bo Sundman, Ursula Kattner and others), is available. The code allows us easily derive thermophysical properties using the results of first-principles calculations (performed using, for example, Quantum Espresso) and to determine the values of very few fitting parameters using least-squares minimization of the errors. The same methodology is being developed for binary systems, taking the Cr-Ni system as an example.
We understand the enormous advantage that the use of the SGTE unary database has brougth to the CALPHAD community, as without these universally accepted standards the constrution of muticomponent databases would not be possible. We hope with the present work to contribute to a better understanding of the physical background of these unary descriptions, to the enlargement of the community involved in this effort and to the discussion of possible new standards.