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We study d 0 ferromagnetism in ZnS quantum dots (QDs) and nanowires (NW). To find the magnetization of the medium and large size nanocrystals (NC), we introduce the surface-bulk (SB) model where the separately calculated surface and bulk contributions to the total magnetic moment allow us to find the magnetization for a large nanocrystal (NC). For nanowire calculations the accuracy of the SB model varies from 0.2% to 21% depending on the Zn vacancy concentrations on the NC surface and in the NC core. We find that the higher the concentration of the Zn vacancies, the larger the total magnetic moment in the nanocrystal. However, the magnetic moment increases faster for quantum dots rather than for nanowires. We also study the cases where the concentrations of Zn vacancies can be different on the NC surface and in the core. From the comparison of the experimental and theoretical NW magnetic moments, we find that the experimental magnetization is 1.4 × 10 3 smaller than the calculated one. Such a huge discrepancy can be explained from the assumption that not all magnetic moments due to Zn vacancy participate in the ferromagnetism, and there are some regions with zero magnetism and uncoupled (paramagnetic) spins. The random orientation of nanoowires could be another reason for the weak ferromagnetism.

We investigate the electronic structure of a planar mononuclear Cu-based molecule [Cu(C6H4S2)2]z in two oxidation states (z = −2, −1) using density-functional theory (DFT) with Fermi–Löwdin orbital (FLO) self-interaction correction (SIC). The dianionic Cu-based molecule was proposed to be a promising qubit candidate. Self-interaction error within approximate DFT functionals renders severe delocalization of electron and spin densities arising from 3d orbitals. The FLO-SIC method relies on optimization of Fermi–Löwdin orbital descriptors (FODs) with which localized occupied orbitals are constructed to create SIC potentials. Starting with many initial sets of FODs, we employ a frozen-density loop algorithm within the FLO-SIC method to study the Cu-based molecule. We find that the electronic structure of the molecule remains unchanged despite somewhat different final FOD configurations. In the dianionic state (spin S = 1/2), FLO-SIC spin density originates from the Cu d and S p orbitals with an approximate ratio of 2:1, in quantitative agreement with multireference calculations, while in the case of SIC-free DFT, the orbital ratio is reversed. Overall, FLO-SIC lowers the energies of the occupied orbitals and, in particular, the 3d orbitals unhybridized with the ligands significantly, which substantially increases the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) compared to SIC-free DFT results. The FLO-SIC HOMO–LUMO gap of the dianionic state is larger than that of the monoanionic state, which is consistent with experiment. Our results suggest a positive outlook of the FLO-SIC method in the description of magnetic exchange coupling within 3d-element-based systems.

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