# BerkeleyGW overview

BerkeleyGW is a massively parallel computational package for electron excited-state properties that is based on the many-body perturbation theory employing the ab initio GW and GW plus Bethe-Salpeter equation methodology.

It is able to calculate accurate electronic and optical properties in materials of different dimensionalities and complexity, from bulk semiconductors and metals to nanostructured materials and molecules.

It can be used in conjunction with many density-functional theory codes for ground-state properties, including PARATEC, Abinit, PARSEC, Quantum ESPRESSO, OCTOPUS and SIESTA. These codes are used to generate initial files, containing the ground-state density and wavefunctions from density-functional theory, see Mean-Field.

For a theoretical overview of the main steps in a BerkeleyGW calculation, please see the following links:

1. GW calculation:
1. epsilon - evaluating the dielectric screening
2. sigma - calculating the self-energy
2. Bethe-Salpeter equation (BSE) caclculation:
1. kernel - calculating the electron-hole interaction
2. absorption - evaluate optical and excited-state properties.

For practical details of how to perform each part of the calculation, as well as an overview of input keywords, see the Typical workflow section.