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Register a new userElectronic structure of zinc-blende MnTe within the GW approximation
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Using the local spin-density approximation (LSDA) and the (non self-consistent) GW approach, the (quasi-particle) band structure is calculated for MnTe in zinc-blende geometry. Different parameters characterizing the electronic structure are computed for an antiferromagnetic and the ferromagnetic phase and compared with the experiment. The strong Hubbard-type repulsion on the Mn-3d orbitals and the p-d hybridization are seen to be responsible for substantial defects found in the LSDA picture. It is discussed to which extent these can be improved upon by means of the GW approach.
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The quasiparticle band structures of 3d transition metals, ferromagnetic Fe, Ni and paramagnetic Cu, are calculated by the GW approximation. The width of occupied 3d valence band, which is overestimated in the LSDA, is in good agreement with experimental observation. However the exchange splitting and satellite in spectra are not reproduced and it is required to go beyond the GW approximation. The effects of static screening and dynamical correlation are discussed in detail in comparison with the results of the static COHSEX approximation. The dynamical screening effects are important for band width narrowing.
In many-body perturbation theory (MBPT) the self-energy Sigma=iGWGamma plays the key role since it contains all the many body effects of the system. The exact self-energy is not known; as first approximation one can set the vertex function Gamma to unity which leads to the GW approximation. The latter properly describes the high-density regime, where screening is important; in the low-density regime, instead, other approximations are proposed, such as the T matrix, which describes multiple scattering between two particles. Here we combine the two approaches. Starting from the fundamental equations of MBPT we show how one can derive the T-matrix approximation to the self-energy in a common framework with GW. This allows us to elucidate several aspects of this formulation, including the origin of, and link between, the electron-hole and the particle-particle T matrix, the derivation of a screened T matrix, and the conversion of the T matrix into a vertex correction. The exactly solvable Hubbard molecule is used for illustration.
We present the results of calculations for Pu and Am performed using an implementation of self-consistent relativistic GW method. The key feature of our scheme is to evaluate polarizability and self-energy in real space and Matsubaras time. We compare our GW results with the calculations using local density (LDA) and quasiparticle (QP) approximations and also with scalar-relativistic calculations. By comparing our calculated electronic structures with experimental data, we highlight the importance of both relativistic effects and effects of self-consistency in this GW calculation.
The properties of neutral acceptor states in zinc-blende semiconductors are re-examined in the frame of extended-basis $sp^3d^5s^*$ tight-binding model. The symmetry discrepancy between envelope function theory and atomistic calculations is explained in terms of over symmetric potential in current k$cdot$p approaches. Spherical harmonics decomposition of microscopic Local Density Of States (LDOS) allows for the direct analysis of the tight-binding results in terms of envelope function. Lifting of degeneracy by strain and electric field and their effect on LDOS is examined. The fine structure of magnetic impurity caused by exchange interaction of hole with impurity $d$-shell and its dependence on strain is studied. It is shown that exchange interaction by mixing heavy and light hole makes the ground state more isotropic. The results are important in the context of Scanning Tunneling Microscopy (STM) images of subsurface impurities.
We report on first-principles calculations of multilayers of zinc-blende half-metallic ferromagnets CrAs and CrSb with III-V and II-VI semiconductors, in the [001] orientation. We examine the ideal and tetragonalised structures, as well as the case of an intermixed interface. We find that, as a rule, half-metallicity can be conserved throughout the heterostructures, provided that the character of the local coordination and bonding is not disturbed. At the interfaces with semiconductors, we describe a mechanism that can give also a non-integer spin moment per interface transition atom, and derive a simple rule to evaluate it.
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