Quasiparticle band structure based on a generalized Kohn-Sham scheme

We present a comparative full-potential study of generalized Kohn-Sham schemes (gKS) with explicit focus on their suitability as starting point for the solution of the quasiparticle equation. We compare $G_0W_0$ quasiparticle band structures calculated upon LDA, sX, HSE03, PBE0, and HF functionals for exchange and correlation (XC) for Si, InN and ZnO. Furthermore, the HSE03 functional is studied and compared to the GGA for 15 non-metallic materials for its use as a starting point in the calculation of quasiparticle excitation energies. For this case, also the effects of selfconsistency in the $GW$ self-energy are analysed. It is shown that the use of a gKS scheme as a starting point for a perturbative QP correction can improve upon the deficiencies found for LDA or GGA staring points for compounds with shallow $d$ bands. For these solids, the order of the valence and conduction bands is often inverted using local or semi-local approximations for XC, which makes perturbative $G_0W_0$ calculations unreliable. The use of a gKS starting point allows for the calculation of fairly accurate band gaps even in these difficult cases, and generally single-shot $G_0W_0$ calculations following calculations using the HSE03 functional are very close to experiment

GW band structure of InAs and GaAs in the wurtzite phase

We report the first quasiparticle calculations of the newly observed wurtzite polymorph of InAs and GaAs. The calculations are performed in the GW approximation using plane waves and pseudopotentials. For comparison we also report the study of the zinc-blende phase within the same approximations. In the InAs compound the In 4d electrons play a very important role: whether they are frozen in the core or not, leads either to a correct or a wrong band ordering (negative gap) within the Local Density Appproximation (LDA). We have calculated the GW band structure in both cases. In the first approach, we have estimated the correction to the pd repulsion calculated within the LDA and included this effect in the calculation of the GW corrections to the LDA spectrum. In the second case, we circumvent the negative gap problem by first using the screened exchange approximation and then calculating the GW corrections starting from the so obtained eigenvalues and eigenfunctions. This approach leads to a more realistic band-structure and was also used for GaAs. For both InAs and GaAs in the wurtzite phase we predict an increase of the quasiparticle gap with respect to the zinc-blende polytype.Comment: 9 pages, 6 figures, 3 table

Universality of electron accumulation at wurtzite c- and a-plane and zinc-blende InN surfaces

Electron accumulation is found to occur at the surface of wurtzite (112¯0), (0001), and (0001¯) and zinc-blende (001) InN using x-ray photoemission spectroscopy. The accumulation is shown to be a universal feature of InN surfaces. This is due to the low Г-point conduction band minimum lying significantly below the charge neutrality level

Novel Reconstruction Mechanism for Dangling-Bond Minimization: Combined Method Surface Structure Determination of SiC(111)-(3×3)

The SiC(111)−(3×3) phase was analyzed by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED) holography, density functional theory (DFT), and conventional LEED. A single adatom per unit cell found in STM acts as a beam splitter for the holographic inversion of discrete LEED spot intensities. The resulting 3D image guides the detailed analyses by LEED and DFT which find a Si tetramer on a twisted Si adlayer with cloverlike rings. This twist model with one dangling bond left per unit cell represents a novel (n×n)-reconstruction mechanism of group-IV (111) surfaces

Electronic structure of the (111) and (-1-1-1) surfaces of cubic BN: A local-density-functional ab initio study

We present ab initio local-density-functional electronic structure calculations for the (111) and (-1-1-1) surfaces of cubic BN. The energetically stable reconstructions, namely the N adatom, N3 triangle models on the (111), the (2x1), boron and nitrogen triangle patterns on the (-1-1-1) surface are investigated. Band structure and properties of the surface states are discussed in detail.Comment: 8 pages, 12 figure

Electronic structure and the minimum conductance of a graphene layer on SiO2 from density-functional methods.

The effect of the SiO$_2$ substrate on a graphene film is investigated using realistic but computationally convenient energy-optimized models of the substrate supporting a layer of graphene. The electronic bands are calculated using density-functional methods for several model substrates. This provides an estimate of the substrate-charge effects on the behaviour of the bands near $E_F$, as well as a variation of the equilibrium distance of the graphene sheet. A model of a wavy graphene layer is examined as a possible candidate for understanding the nature of the minimally conducting states in graphene.Comment: 6 pages, 5 figure

Accurate calculation of polarization-related quantities in semiconductors

We demonstrate that polarization-related quantities in semiconductors can be predicted accurately from first-principles calculations using the appropriate approach to the problem, the Berry-phase polarization theory. For III-V nitrides, our test case, we find polarizations, polarization differences between nitride pairs, and piezoelectric constants quite close to their previously established values. Refined data are nevertheless provided for all the relevant quantities.Comment: RevTeX 4 pages, no figure

All electron and pseudopotential study of the spin polarization of the V (001) surface: LDA versus GGA

The spin-polarization at the V(001) surface has been studied by using different local (LSDA) and semilocal (GGA) approximations to the exchange-correlation potential of DFT within two ab initio methods: the all-electron TB-LMTO-ASA and the pseudopotential LCAO code SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms). A comparative analysis is performed first for the bulk and then for a N-layer V(001) film (7 < N < 15). The LSDA approximation leads to a non magnetic V(001) surface with both theoretical models in agreement (disagreement) with magneto-optical Kerr (electron-capture spectroscopy) experiments. The GGA within the pseudopotential method needs thicker slabs than the LSDA to yield zero moment at the central layer, giving a high surface magnetization (1.70 Bohr magnetons), in contrast with the non magnetic solution obtained by means of the all-electron code.Comment: 12 pages, 1 figure. Latex gzipped tar fil