Combining GW calculations with exact-exchange density-functional theory: An analysis of valence-band photoemission for compound semiconductors

The journey of theoretical study on semiconductors is reviewed in a non-conventional way. We have started with the basic introduction of Hartree-Fock method and introduce the fundamentals of Density Functional Theory (DFT). From the oldest Local Density Approximations (LDA) to the most recent developments of semi-local corrections [Generalised Gradient Approximation (GGA), Meta-GGAs], hybrid functionals and orbital dependent methodologies are discussed in detail. To showcase ...

We have studied the electronic structure of InN and GaN employing G0W0 calculations based on exact-exchange density-functional theory. For InN our approach predicts a gap of 0.7 eV. Taking the Burnstein-Moss effect into account, the increase of the apparent quasiparticle gap with increasing electron concentration is in good agreement with the observed blue shift of the experimental optical absorption edge. Moreover, the concentration dependence of the effective mass, which re...

In electronic structure calculations the optimized effective potential (OEP) is a method that treats exchange interactions exactly using a local potential within density-functional theory (DFT). We present a method using density functional perturbation theory combined with the Hylleraas variational method for finding the OEP by direct minimization which avoids any sum over unoccupied states. The method has been implemented within the plane-wave, pseudopotential formalism. Ban...

We present a comprehensive study of the photon energy dependence of the valence band photoemission yield in the prototype Mott-Hubbard oxide V2O3. The analysis of our experimental results, covering an extended photon energy range (20-6000 eV) and combined with GW calculations, allow us to identify the nature of the orbitals contributing to the total spectral weight at different binding energies, and in particular to locate the V 4s at about 8 eV binding energy. From this co...

We use fully self-consistent GW calculations on diamond and silicon carbide to reparametrize the Heyd-Scuseria-Ernzerhof exact exchange density functional for use in band structure calculations of semiconductors and insulators. We show that the thus modified functional is able to calculate the band structure of bulk Si, Ge, GaAs, and CdTe with good quantitative accuracy at a significantly reduced computational cost as compared to GW methods. We discuss the limitations of this...

We report calculated, electronic and related properties of wurtzite and zinc blende gallium nitrides (w-GaN, zb-GaN). We employed a local density approximation (LDA) potential and the linear combination of atomic orbital (LCAO) formalism. The implementation of this formalism followed the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). The calculated electronic and related properties, for both structures of GaN, are in good agreement with...

Computing the $GW$ quasiparticle bandstructure and Bethe-Salpeter Equation (BSE) absorption spectra for materials with spin-orbit coupling has commonly been done by treating $GW$ corrections and spin-orbit coupling as separate perturbations to density-functional theory. However, accurate treatment of materials with strong spin-orbit coupling often requires a fully relativistic approach using spinor wavefunctions in the Kohn-Sham equation and $GW$/BSE. Such calculations have o...

Exact exchange (EXX) Kohn-Sham calculations within an all-electron full-potential method are performed on a range of semiconductors and insulators (Ge, GaAs, CdS, Si, ZnS, C, BN, Ne, Ar, Kr and Xe). We find that the band-gaps are not as close to experiment as those obtained from previous pseudopotential EXX calculations. Full-potential band-gaps are also not significantly better for $sp$ semiconductors than for insulators, as had been found for pseudopotentials. The locations...

A predicted type-II staggered band alignment with an approximately $1.4 eV$ valence band offset at the $ZnGeN_2/GaN$ heterointerface has inspired novel band-engineered $III-N/ZnGeN_2$ heterostructure-based device designs for applications in high performance optoelectronics. We report on the determination of the valence band offset between metalorganic chemical vapor deposition grown $(ZnGe)_{1-x}Ga_{2x}N_2$, for $x = 0$ and $0.06$, and $GaN$ using X-ray photoemission spectros...

We describe an all-electron $G_0W_0$ implementation for periodic systems with $k$-point sampling implemented in a crystalline Gaussian basis. Our full-frequency $G_0W_0$ method relies on efficient Gaussian density fitting integrals and includes both analytic continuation and contour deformation schemes. Due to the compactness of Gaussian bases, no virtual state truncation is required as is seen in many plane-wave formulations. Finite size corrections are included by taking th...