Spin-dependent interactions in orbital-density-dependent functionals: non-collinear Koopmans spectral functionals

Abstract

The presence of spin-orbit coupling or non-collinear magnetic spin states can have dramatic effects on the ground-state and spectral properties of materials, in particular on the band structure. Here, we develop non-collinear Koopmans-compliant functionals based on Wannier functions and density-functional perturbation theory, targeting accurate spectral properties in the quasiparticle approximation. Our non-collinear Koopmans-compliant theory involves functionals of four-component orbitals densities, that can be obtained from the charge and spin-vector densities of Wannier functions. We validate our approach on four emblematic non-magnetic and magnetic semiconductors where the effect of spin-orbit coupling goes from small to very large: the III-IV semiconductor GaAs, the transition-metal dichalcogenide WSe${}_2$, the cubic perovskite CsPbBr${}_3$, and the ferromagnetic semiconductor CrI${}_3$. The predicted band gaps are comparable in accuracy to state-of-the-art many-body perturbation theory and include spin-dependent interactions and screening effects that are missing in standard diagrammatic approaches based on the random phase approximation. While the inclusion of orbital- and spin-dependent interactions in many-body perturbation theory requires self-screening or vertex corrections, they emerge naturally in the Koopmans-functionals framework.

16 pages, 6 figures, 4 tables + supplementary material (5 pages): added simulations and discussion for ferromagnetic bulk CrI3, added references, fixed typos

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Cited by in corpus (3)

• The Wannier Function Software Ecosystem for Materials Simulations
• Predicting electronic screening for fast Koopmans spectral functional calculations
• Predicting the suitability of photocatalysts for water splitting using Koopmans spectral functionals: The case of TiO${}_2$ polymorphs