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MA: Fachverband Magnetismus

MA 41: Poster III

MA 41.21: Poster

Donnerstag, 20. März 2025, 15:00–17:30, P3

Exact exchange kernel for spin waves in the spin-polarized homogeneous electron gas — •Michael Neugum, Alexandre Borrameo Alcaïde, and Arno Schindlmayr — Universität Paderborn, Department Physik, 33095 Paderborn, Germany

Spin waves represent an important class of elementary excitations in magnetically ordered materials. Ab initio spin-wave calculations for real materials are often based on time-dependent density-functional theory. The crucial ingredient is the so-called exchange-correlation kernel, which incorporates the effects of the Coulomb interaction between the electrons. In general, the kernel is wavevector and frequency dependent, although its exact mathematical form is unknown. Practical implementations typically employ the adiabatic local-density approximation (ALDA), where the kernel is replaced by a simple constant. The results are generally in good qualitative agreement with experimental measurements but sometimes exhibit significant quantitative deviations. In this work, we implement the exact exchange kernel, which is based on a diagrammatic expansion to first order in the Coulomb interaction. We show results for the fully spin-polarized homogeneous electron gas in two and three dimensions. Overall, we observe a substantial discrepancy from the ALDA. In particular, the parabolic component of the dispersion, the spin-wave stiffness, is systematically lower for the exact exchange kernel. While the exact exchange kernel depends both on wavevector and frequency, the most significant effects are due to the wavevector dependence, whereas the frequency dependence may be neglected for practical purposes.

Keywords: spin waves; spin-polarized electron gas; exact exchange kernel; time-dependent density-functional theory