Investigation of Fe by means of atomistic spin dynamics coupled with ab initio molecular dynamics simulations

Ab initio molecular dynamics (AIMD) is a mature approach for the investigation of nonmagnetic materials. Magnetism in condensed matter, however, introduces a further challenge for the theoretical community. A recently developed method that allows to take advantage of the accuracy of AIMD and couples the magnetic and vibrational degrees of freedom is the atomistic spin dynamics - ab initio molecular dynamics (ASD-AIMD) method [1]. In this approach, the atomic and magnetic dynamics are run in parallel while communicating with each other. The applicability of the method has been shown in the study of CrN, a semiconducting system with well localized magnetic moments.
Here, we employ ASD-AIMD simulations to investigate Fe near its Curie temperature. Being Fe a ferromagnetic metal, temperature induces fluctuations not only on the transversal magnetic degrees of freedom, but also on the longitudinal ones, which are often considered irrelevant for a system like bcc Fe. In our simulations we include this type of excitations through a mean-field entropic term, and we compare results in absence of this effect. This work is a pre-step in the calculation of free energy differences in magnetic systems with ab initio accuracy.
[1] Stockem et al., Physical Review Letters 121, 125902 (2018)