Influence of interaction energies between carbon atoms in FCC iron on concentration dependence of carbon activity

The first-principle simulation of the interaction energies of carbon atoms in FCC iron was carried out using the software package WIEN2k. They amounted to E1 = 0.06 eV, E2 = 0.1 eV and E3 = 0.005 eV (interaction energies between carbon atoms located on the first, second and third spheres of coordination of interstitial sublattice of FCC iron). The full potential linear augmented plane-wave (LAPW) method within the generalized gradient approximation PBE-GGA in the supercell of 32 iron atoms with periodic boundary conditions was used in the investigation. This is the most powerful technique in the framework of Density Functional Theory. In order to check the reliability of found energy values, the concentration dependence of carbon activity in FCC iron was built using Monte-Carlo simulation. The good qualitative agreement of activity curve obtained with our interaction energies with the experimental one indicates the reliability of C-C interaction energy and performance of our model of paramagnetic state. Accounting of data on interaction on the third sphere of coordination does not significantly affect the calculation results. This is due to a very low value of the interaction energy of carbon atoms in FCC-iron on the third sphere of coordination.