Electronic correlations determine the phase stability of iron up to the   melting temperature
  We present theoretical results on the high-temperature phase stability and phonon spectra of paramagnetic bcc iron which explicitly take into account many-body effects. 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 is found to be highly anharmonic and appears to be stabilized by the lattice entropy. 
I. Leonov, A. I. Poteryaev, Yu. N. Gornostyrev, A. I. Lichtenstein, M.   I. Katsnelson, V. I. Anisimov, and D. Vollhardt
cond-mat.str-el cond-mat.mtrl-sci