Electronic properties of interfaces and defects from many-body perturbation theory: Recent developments and applications

We review some recent developments in many-body perturbation theory (MBPT) calculations that have enabled the study of interfaces and defects. Starting from the theoretical basis of MBPT, Hedin's equations are presented, leading to the GW and GWΓ approximations. We introduce the perturbative approach, that is the one most commonly used for obtaining quasiparticle (QP) energies. The practical strategy presented for dealing with the frequency dependence of the self-energy operator is based on either plasmon-pole models (PPM) or the contour deformation technique, with the latter being more accurate. We also discuss the extrapolar method for reducing the number of unoccupied states which need to be included explicitly in the calculations. The use of the PAW method in the framework of MBPT is also described. Finally, results which have been obtained using MBPT for band offsets at interfaces and for defects are presented, with emphasis on the main difficulties and caveats. Schematic representation of the QP corrections (marked with δ) to the band edges (E_v and E_c) and a defect level (E_d) for a Si/SiO₂ interface (Si and O atoms are represented in blue and red, respectively, in the ball-and-stick model) with an oxygen vacancy leading to a Si-Si bond (the Si atoms involved in this bond are colored light blue).