Regensburg 2013 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 31: Computational Materials Modelling - Diffusion & Kinetics II

MM 31.5: Talk

Wednesday, March 13, 2013, 11:15–11:30, H24

First-principles thermodynamics of paramagnetic fcc iron — •Fritz Körmann, Blazej Grabowski, Biswanath Dutta, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, D-40237, Düsseldorf, Germany

A key issue of thermodynamic first-principles modeling of paramagnetic materials is the interplay of magnetic and atomic degrees of freedom. Practical approaches allowing the computation of atomic forces at finite magnetic temperatures are up to now only rarely available, but are decisive for an accurate description of the thermodynamics in many material systems. For example, first-principles predictions for paramagnetic iron are typically based on empirical approximations, e.g., the 2-states spin model. For this reason, we have recently developed an ab initio approach to obtain effective paramagnetic atomic forces [1]. They are obtained from SQS structures for the magnetic disorder combined with a spin-space averaging procedure. Employing this method we calculate the paramagnetic quasi-harmonic (vibrational) free energy for fcc iron. Adding electronic and magnetic contributions we obtain the complete free energy surface. The derived thermodynamic properties such as phonon spectrum, expansion coefficient, and bulk modulus are in good agreement with experiment.

[1] F. Körmann, A. Dick, B. Grabowski, T. Hickel, and J. Neugebauer, Phys. Rev. B 85, 125104 (2012).