We use an analytical model to describe the magnetocrystalline anisotropy energy (MAE) in solids as a function of band filling. The MAE is evaluated in second-order perturbation theory, which makes it possible to decompose the MAE into a sum of transi
tions between occupied and unoccupied pairs. The model enables us to characterize the MAE as a sum of contributions from different, often competing terms. The nitridometalates Li$_{2}$[(Li$_{1-x}$T$_{x}$)N], with $T$=Mn, Fe, Co, Ni, provide a system where the model is very effective because atomic like orbital characters are preserved and the decomposition is fairly clean. Model results are also compared against MAE evaluated directly from first-principles calculations for this system. Good qualitative agreement is found.
The spin-orbit interaction generally leads to spin splitting (SS) of electron and hole energy states in solids, a splitting that is characterized by a scaling with the wavevector $bf k$. Whereas for {it 3D bulk zincblende} solids the electron (heavy
hole) SS exhibits a cubic (linear) scaling with $k$, in {it 2D quantum-wells} the electron (heavy hole) SS is currently believed to have a mostly linear (cubic) scaling. Such expectations are based on using a small 3D envelope function basis set to describe 2D physics. By treating instead the 2D system explicitly in a multi-band many-body approach we discover a large linear scaling of hole states in 2D. This scaling emerges from hole bands coupling that would be unsuspected by the standard model that judges coupling by energy proximity. This discovery of a linear Dresselhaus k-scaling for holes in 2D implies a different understanding of hole-physics in low-dimensions.
We present first-principles calculations of the impact ionization rate (IIR) in the $GW$ approximation ($GW$A) for semiconductors. The IIR is calculated from the quasiparticle (QP) width in the $GW$A, since it can be identified as the decay rate of a
QP into lower energy QP plus an independent electron-hole pair. The quasiparticle self-consistent $GW$ method was used to generate the noninteracting hamiltonian the $GW$A requires as input. Small empirical corrections were added so as to reproduce experimental band gaps. Our results are in reasonable agreement with previous work, though we observe some discrepancy. In particular we find high IIR at low energy in the narrow gap semiconductor InAs.
We present a new full-potential method to solve the one-body problem, for example, in the local density approximation. The method uses the augmented plane waves (APWs) and the generalized muffin-tin orbitals (MTOs) together as basis sets to represent
the eigenfunctions. Since the MTOs can efficiently describe localized orbitals, e.g, transition metal 3$d$ orbitals, the total energy convergence with basis size is drastically improved in comparison with the linearized APW method. Required parameters to specify MTOs are given by atomic calculations in advance. Thus the robustness, reliability, easy-of-use, and efficiency at this method can be superior to the linearized APW and MTO methods. We show how it works in typical examples, Cu, Fe, Li, SrTiO$_3$, and GaAs.
We present spin wave dispersions in MnO, NiO, and $alpha$-MnAs based on the quasiparticle self-consistent $GW$ method (qsgw), which determines an optimum quasiparticle picture. For MnO and NiO, qsgw results are in rather good agreement with experimen
ts, in contrast to the LDA and LDA+U description. For $alpha$-MnAs, we find a collinear ferromagnetic ground state in qsgw, while this phase is unstable in the LDA.
