Advanced computational methods for an accurate thermodynamic description of the paramagnetic state of magnetic materials from first principles

In the past years, procedures to calculate from first principles the (Gibbs) free energy of a system with arbitrary accuracy have been established, starting in general from a simplified model and then calculating the full free energy with the use of statistical sampling techniques. These methods have been proven powerful for many materials; however, when it comes to magnetic materials at finite temperature, the system becomes more complex to be treated with ab initio techniques because of the indirect influence of magnetism on several equilibrium properties, besides its explicit contribution to the free energy.
To improve the description of magnetic materials in the high temperature paramagnetic phase from first principles, we develop a method [Physical Review B 98, 064105 (2018)] to perform structural relaxations in the paramagnetic phase based on the disordered local moment (DLM) model, and we apply it to the case of a vacancy and a C interstitial in bcc Fe, bcc Fe_1-xCr_x random alloys, and defects in CrN. We also apply the recently developed atomistic spin dynamics-ab initio molecular dynamics approach [Physical Review Letters 121, 125902 (2018)] to defect free bcc Fe at the Curie temperature to prove the feasibility of free energy calculations on this system.