Volume 224, 2020

Subsystem density-functional theory for interacting open-shell systems: spin densities and magnetic exchange couplings

Abstract

We investigate the possibility of describing interacting open-shell systems in high-spin and broken-symmetry (BS) states with subsystem density-functional theory (sDFT). This subsystem method typically starts from the electronic-structure results obtained for individual systems, for which the spin states can be individually defined. Through the confining effect of the embedding potential and/or the use of monomer basis sets, these individual spin states can be preserved in sDFT calculations. This offers the possibility of easy convergence to broken-symmetry states with arbitrary local spin patterns. We show that the resulting spin densities are in very good agreement with successfully converged broken-symmetry Kohn–Sham density-functional theory (KS-DFT) calculations. Yet sDFT can even cure those BS cases where KS-DFT suffers from convergence problems or convergence to undesired spin states. In contrast to KS-DFT, the sDFT-results only show a mild exchange–correlation functional dependence. We also show that magnetic coupling constants from sDFT are not satisfactory with standard approximations for the non-additive kinetic energy. When this component is evaluated “exactly”, i.e. based on potential reconstruction, however, the magnetic coupling constants derived from spin-state energy differences are greatly improved. Hence, the interacting radicals studied here represent cases where even (semi-)local approximations for the non-additive kinetic-energy potential work well, while the parent energy functionals do not yield satisfactory results for spin-state energy differences.

Graphical abstract: Subsystem density-functional theory for interacting open-shell systems: spin densities and magnetic exchange couplings

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
15 May 2020
Accepted
14 Tem 2020
First published
01 Eki 2020

Faraday Discuss., 2020,224, 201-226

Subsystem density-functional theory for interacting open-shell systems: spin densities and magnetic exchange couplings

A. Massolle and J. Neugebauer, Faraday Discuss., 2020, 224, 201 DOI: 10.1039/D0FD00063A

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