# Mean-field calculations

The BerkeleyGW software package uses many-body perturbation-theory formalisms; therefore, one needs to provide a reasonable mean-field starting point for the perturbation-theory calculations. For most application, density-functional theory (DFT) based on semilocal functionals provide a good starting point for GW and GW-BSE calculations.

The following mean-field codes are currently supported by BerkeleyGW:

- Quantum ESPRESSO
- Abinit
- Octopus
- PARATEC
- PARSEC
- EPM (Empirical Pseudopotential Method)
- RMGDFT
- Siesta
- JDFTx

In addition, we include a wrapper to convert mean-field quantities to the StochasticGW code.

We provide a library to easily write mean-field-related quantities in the format used by BerkeleyGW.

BerkeleyGW requires the following quantities from mean-field codes:

- Mean-field eigenvalues and eigenvectors, stored in
`WFN`

files, for arbitrary k-point grids. - The mean-field exchange-correlation matrix elements,
`vxc.dat`

, or exchange-correlation matrix in reciprocal space,`VXC`

. - Ground-state charge density \rho(G), stored in
`RHO`

-- only for calculations based on the generalized plasmon-pole (GPP) model.

For further information on how to use each mean-field code with the appropriate wrapper for BerkeleyGW, we refer to the BerkeleyGW tutorials. We also present some notes on potential issues arising when running GW calculations starting from different mean-field codes in a separate page.