Phonon dispersions of bcc Fe around the Curie temperature from ab initio molecular dynamics

Iron (Fe) is a polymorph with a great variety of applications. At the lowest pressures and temperatures it has the bcc structure whereas at high temperatures it crystallizes in the fcc structure. The bcc phase is ferromagnetic below its Curie temperature of 1043 K and it remains in the bcc phase while paramagnetic before finally transforming to fcc at 1183 K. We performed density functional theory (DFT) molecular dynamics calculations in the Born-Oppenheimer approximation of ferromagnetic and paramagnetic bcc iron at temperatures close to the Curie temperature. Effective interatomic forces constants up to fifth nearest-neighbors were calculated from the dynamics calculations and used to generate phonon dispersions and density of states curves. A softening of the phonons in the Γ to N direction is observed, and we discuss this and other trends.