The BerkeleyGW package is a set of computer codes that calculates the
quasiparticle properties and the optical responses of a large variety of
materials from bulk periodic crystals to nanostructures such as slabs, wires and
molecules. The package takes as input the mean-field results from various
electronic structure codes such as the Kohn-Sham DFT eigenvalues and
eigenvectors computed with PARATEC, Quantum ESPRESSO, SIESTA, PARSEC, Abinit,
Octopus, or TBPW (aka EPM). The package consists of the three main component
codes:
* Epsilon computes the irreducible polarizability in the Random Phase
  Approximation and uses it to generate the dielectric matrix and its inverse.
* Sigma computes the self-energy corrections to the DFT eigenenergies using the
  GW approximation of Hedin and Lundqvist, applying the first-principles
  methodology of Hybertsen and Louie within the generalized plasmon-pole model
  for the frequency-dependent dielectric matrix.
* BSE solves the Bethe-Salpeter equation for correlated electron-hole excitations.