Free energy of bcc iron: Integrated ab initio derivation of vibrational, electronic and magnetic contributions
F. Körmann, A. Dick, B. Grabowski, B. Hallstedt, T. Hickel, J. Neugebauer.
Physical Review B, 78, 033102,1-4, (2008)
We present ab initio derived thermodynamic properties of ferromagnetic bcc iron up to the bcc-fcc phase transition temperature (1200 K), including vibrational, electronic, and magnetic contributions. The quasiharmonic approximation and finite-temperature density-functional theory are employed to account for vibrational and electronic excitations. The magnetic contribution is derived from the solution of the quantum Heisenberg model within many-body theory using the mean-field and random-phase approximation. The calculated thermodynamic properties show an excellent agreement with available experimental data and reveal the necessity to consider all three types of excitations.