Category:Many-Body Perturbation Theory

Theory

GW and RPA are post-DFT methods used to solve the many-body problem approximatively.

RPA stands for the random phase approximation is often used as synonym for the adiabatic connection fluctuation dissipation theorem (ACFDT). RPA/ACFDT provides access to the correlation energy of a system and can be understood in terms of Feynman diagrams as an infinite sum of all bubble diagrams, where excitonic effects (interactions between electrons and holes) are neglected. The RPA/ACFDT is used as a post-processing tool to determine a more accurate groundstate energy.

The GW approximation goes hand in hand with the RPA, since the very same diagrammatic contributions are taken into account in the screened Coulomb interaction of a system often denoted as W. However, in contrast to the RPA/ACFDT, the GW method provides access to the spectral properties of the system by means of determining the energies of the quasi-particles of a system using a screened exchange-like contribution to the self-energy. The GW approximation is currently one of the most accurate many-body methods to calculate band-gaps.

More information about the theoretical background is found on following pages:

• RPA/ACFDT: Correlation energy in the Random Phase Approximation .
• The GW approximation of Hedin's equations.

How to

Practical guides to different diagrammatic approximations are found on following pages:

• ACFDT: ACFDT/RPA calculations.
• GW: Practical guide to GW calculations.
• BSE: BSE calculations.
• Using the GW routines for the determination of frequency dependent dielectric matrix: GW and dielectric matrix.
• MP2 method: MP2 ground state calculation - Tutorial.