Structural $\gamma \text{-}\epsilon$ phase transition in Fe-Mn alloys from CPA+DMFT approach

We present a computational scheme for total energy calculations of disordered alloys with strong electronic correlations. It employs the coherent potential approximation combined with the dynamical mean-field theory and allows one to study the structural transformations. The material-specific Hamiltonians in the Wannier function basis are obtained by density functional theory. The proposed computational scheme is applied to study the $\gamma \text{-}\epsilon$ structural transition in paramagnetic Fe-Mn alloys for Mn content from 10 to 20 at. %. The electronic correlations are found to play a crucial role in this transition. The calculated transition temperature decreases with increasing Mn content and is in a good agreement with experiment. We demonstrate that in contrast to the $\alpha \text{-}\gamma$ transition in pure iron, the $\gamma \text{-}\epsilon$ transition in Fe-Mn alloys is driven by a combination of kinetic and Coulomb energies. The latter is found to be responsible for the decrease of the $\gamma \text{-}\epsilon$ transition temperature with Mn content.