Theory of the sp-d coupling of transition metal impurities with free carriers in ZnO.

The [Formula: see text] exchange coupling between the spins of band carriers and of transition metal (TM) dopants ranging from Ti to Cu in ZnO is studied within the density functional theory. The [Formula: see text] corrections are included to reproduce the experimental ZnO band gap and the dopant levels. The p-d coupling reveals unexpectedly complex features.

Calculated optical properties of Co in ZnO: internal and ionization transitions.

Previous luminescence and absorption experiments in Co-doped ZnO revealed two ionization and one intrashell transition of [Formula: see text] electrons. Those optical properties are analyzed within the generalized gradient approximation to the density functional theory. The two ionization channels involve electron excitations from the two [Formula: see text] gap states, the [Formula: see text] triplet and the [Formula: see text] doublet, to the conduction band.

DFT calculations of magnetic anisotropy energy of Ge(1-x)Mn(x)Te ferromagnetic semiconductor.

Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted ferromagnetic semiconductor Ge(1-x)Mn(x)Te were performed using OpenMX package with fully relativistic pseudopotentials. The influence of hole concentration and magnetic ion neighbourhood on magnetic anisotropy energy is presented. Analysis of microscopic mechanism of magnetic anisotropy is provided, in particular the role of spin-orbit coupling, spin polarization and spatial changes of electron density are discussed.

Point defects as a test ground for the local density approximation +U theory: Mn, Fe, and V(Ga) in GaN.

Electronic structure of the Mn and Fe ions and of the gallium vacancy V(Ga) in GaN was analysed within the GGA + U approach. First, the +U term was treated as a free parameter, and applied to p(N), d(Mn), and d(Fe). The band gap of GaN is reproduced for U(N) ≈ 4 eV.

Theory of nitrogen doping of carbon nanoribbons: edge effects.

Nitrogen doping of a carbon nanoribbon is profoundly affected by its one-dimensional character, symmetry, and interaction with edge states. Using state-of-the-art ab initio calculations, including hybrid exact-exchange density functional theory, we find that, for N-doped zigzag ribbons, the electronic properties are strongly dependent upon sublattice effects due to the non-equivalence of the two sublattices. For armchair ribbons, N-doping effects are different depending upon the ribbon family: for families 2 and 0, the N-induced levels are in the conduction band, while for family 1 the N levels are in the gap.