Electronic correlations determine the phase stability of iron up to the melting temperature

We present results of a theoretical investigation of the phase stability and phonon spectra of paramagnetic iron at high temperatures obtained within the LDA+DMFT scheme. This approach combines {\it ab initio} band-structure methods with dynamical mean-field theory for correlated electrons and allows one to calculate correlation-induced structural transformations and their temperature evolution [1]. We find that electronic correlations determine the structural phase stability of iron up to the melting temperature. Several peculiarities, including a pronounced softening of the [110] transverse $T_1$ mode and a dynamical instability of the $bcc$ lattice in harmonic approximation, are identified. We relate these features to the $\alpha$-to-$\gamma$ and $\gamma$-to-$\delta$ phase transformations in iron. The high temperature $bcc$ phase of iron is found to be highly \textit{anharmonic} and appears to be stabilized by the lattice entropy. This indicates the importance of both electronic correlations and lattice anharmonic effects for a correct description of the high-temperature $\delta$ phase of iron. [1] I.Leonov, A.I.Poteryaev, V.I.Anisimov, D.Vollhardt, PRL {\bf 106}, 106405 (2011); PRB {\bf 85}, 020401 (2012).