Predicting ${\text{d}}^0$ magnetism: Self-interaction correction scheme

Predicting magnetism originating from $2p$ orbitals is a delicate problem, which depends on the subtle interplay between covalency and Hund’s coupling. Calculations based on density-functional theory and the local spin-density approximation fail in two remarkably different ways. On one hand the excessive delocalization of spin-polarized holes leads to half-metallic ground states and the expectation of room-temperature ferromagnetism. On the other hand, in some cases a magnetic ground state may not be predicted at all. We demonstrate that a simple self-interaction correction scheme modifies both these situations via an enhanced localization of the holes responsible for the magnetism and possibly Jahn-Teller distortion. In both cases the ground state becomes insulating and the magnetic coupling between the impurities becomes weak.

Figure 1

(Color online) Total density of states (black line) and density of states projected over the $2p$ shells of the anion acceptor (fill shaded) for MgO doped, respectively, with (a) B, (b) C, and (c) N. The left-hand (right-hand) side plots correspond to LSDA (ASIC). The majority (minority) density of states (DOS) is plotted in the upper (lower) half of each panel.

Figure 2

(Color online) Magnetization isosurfaces calculated with ASIC for ${\text{N}}_{\text{O}}$ in MgO. Note that the $S=1/2$ hole is completely localized along the $p_y$ orbital and it is not evenly distributed along all the bonds. The large spheres are Mg and the smaller spheres are O ions. N is not displayed for clarity.

Figure 3

(Color online) Isosurface of the three holes (the magnetization) associated to $V_{\text{Ga}}$ in GaN as calculated with LSDA (left) and ASIC (right). In LSDA the holes are distributed uniformly over all the four N ions surrounding the vacancy, while they localize around the longer three bonds in ASIC.

Figure 4

(Color online) Isosurface of the hole (the magnetization) associated to ${\text{Zn}}_{\text{Ga}}$ in GaN as calculated with LSDA (left) and ASIC (right). In LSDA the hole is unpolarized and distributed uniformly over all the four N ions surrounding the vacancy, while it spin splits and localizes around the longer bond in ASIC.