# BerkeleyGW overview

BerkeleyGW is a free, open source, and 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 external and well-established 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. In addition, BerkeleyGW also ships with two codes to generate a large number of empty states for GW calculations: SAPO and ParaBands. See the page on mean-field calculations for further information.

After you compile and test BerkeleyGW, we suggest you follow the following tutorials on how to run calculations with BerkeleyGW:

1. GW calculation:
1. epsilon: evaluating the dielectric screening
2. sigma: calculating the electronic self-energy
2. Bethe-Salpeter equation (BSE) calculation:
1. kernel: calculating the electron-hole interaction kernel
2. absorption: computing neutral optical excitation properties, such as optical absorption spectrum.

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.