Speaker
Description
The dipole-dipole interaction—a relativistic term in the Breit-Pauli Hamiltonian—is not treated explicitly in non-relativistic spin density functional theory, its influence on the total energy of periodic systems being neglected due the square of the fine structure constant that scales it. This magnetostatic energy contribution may, in magnetically isotropic systems, be negligible, yet it is not obvious that it remains so in systems where the spin-induced shape anisotropy effect is critical for performance.
We propose here a practical algorithm for non-self-consistent, but non-perturbative, calculations of the spin dipole-dipole correction to the total energy in periodic and molecular systems [1]. To this end, we consider systems with vanishing free current density, in which the magnetization intrinsic to the ground-state spin-density can be associated with a physically fictitious magnetic charge density. We make use of this auxiliary to calculate its associated magnetic scalar potential as defined by Poisson’s equation for magnetism. This potential is then exploited to find the magnetic field, in which the initial magnetization is immersed, ultimately, to generate the non-self-consistent energy correction.
A versatile Mathematica notebook was built to determine the magnetostatic energy contribution for spin-densities in general periodic unit cells, to be used as a post-processing tool with any standard DFT code. Across all systems tested, the algorithm consistently reported the strength of the magnetostatic energy, as compared to the electrostatic energy, consistently on the order of $10^{-5}$, as is expected due to the term’s position in the relativistic expansion. Our approach highlights the possible utility of the magnetic charge density as an intriguing quantity for computing the magnetic properties of quantum systems.
Research funded by Science Foundation Ireland through the Advanced Materials and Bioengineering Research Centre (AMBER, Grant No. 12/RC/2278).
[1] L. MacEnulty and D. D. O’Regan, Journal of Undergraduate Reports in Physics 30, 100005 (2020).
| Speaker Country | Ireland |
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