PROJECTS

Electronic structure and excitation spectra of magnetic materials within first-principles many-body perturbation theory

PRINCIPAL INVESTIGATOR

Dr. Arno Schindlmayr Forschungszentrum Jülich GmbH Institut für Festkörperforschung D-52425 Jülich Germany +49 2461 61 5193 +49 2461 61 2983 a.schindlmayr@fz-juelich.de

TOGETHER WITH

Dr. Gustav Bihlmayer Forschungszentrum Jülich GmbH Institut für Festkörperforschung D-52425 Jülich Germany +49 2461 61 4677 +49 2461 61 2620 G.Bihlmayer@fz-juelich.de

Prof. Dr. Stefan Blügel Forschungszentrum Jülich GmbH Institut für Festkörperforschung D-52425 Jülich Germany +49 2461 61 4249 +49 2461 61 2620 S.Bluegel@fz-juelich.de

ABSTRACT

We develop a computational method based on many-body perturbation theory to enable first-principles calculations of the electronic structure and excitation spectra of magnetic materials, including single quasiparticle and collective magnon excitations as well as their mutual interaction. In a first step we implemented the GW approximation for the electronic self-energy within the all-electron FLAPW method, which allows spin-polarised quasiparticle calculations. At this level, however, the self-energy only describes the coupling to charge fluctuations but not to spin fluctuations. Therefore, we now plan to obtain the transverse spin susceptibility within the same mathematical framework. The poles of this correlation function correspond to the magnon excitation energies, so that materialspecific spectra can be conveniently accessed. The principal computational task is the calculation of the T-matrix that couples electrons and holes in the two spin channels. In order to reduce the numerical cost associated with the construction of this four-point function without compromising first-principles accuracy, we propose a transformation to maximally localised Wannier functions that takes advantage of the short-range nature of the correlation. This may also be used to derive exchange-correlation kernels with memory to be used in time-dependent density-functional theory for magnetic materials. In the future, the two schemes will be combined to incorporate magnon scattering in the self-energy, which strongly influences the lifetime of quasiparticle excitations.

PUBLICATIONS

C. Friedrich, A. Schindlmayr, S. Blügel, T. Kotani,
Elimination of the linearization error in GW calculations based on the linearized augmented-plane-wave method,
Phys. Rev. B 74, 045104 (2006)