$G_0W_0$()

Background

Standard functionals (LDA and GGA), systematically underestimate band gaps, giving values that are about 30-40% smaller than experimental data. The inability of standard Kohn-Sham (KS) theory to give band gaps close to experiment is often referred to as the band-gap problem. From a theoretical point of view this is not surprising since KS eigenvalues are not supposed to give the correct band energies. The band structure of a crystal is rigorously defined as the energies needed to add or subtract electrons from the many-body system which, in turn, are related to the difference between total energies of many-body states differing by one electron.

An alternative, more traditional, approach to the study of exchange-correlation effects in many-body systems is provided by Many-Body Perturbation Theory (MBPT) which defines a rigorous approach to the description of excited-state properties, based on the Green's function formalism. In this lesson, we discuss how to use the MBPT part of ABINIT to compute the band-structure of silicon within the so-called $G_0W_0$ approximation.

For a very brief introduction to the many-body formalism, see MBPTNNOTES (http://www.abinit.org/documentation/helpfiles/for-v7.10/tutorial/theory_mbt.html).

Related ABINIT variables

    •   optdriver

    •   ecuteps

    •   ecutsigx

    •   nband

    •   gwcalctyp

    •   gw_qprange

    •   all gw** variables

The full description, directly from the abinit documentation, is available via the following shell command:

        abidoc.py man inputvariable

This command will print the official description of inputvariable.

The course of this lesson