What is GW approximation? Is it implemented in SIESTA?
The GW approximation, it is one of the approaches for tackling the DFT issues in the description of optical properties. The GW approximation improves charge transfer description, band gap, and conduction band characteristics.
Currently, there is only the possibility of combining SIESTA with other codes, in which the GW approximation is implemented. For example, Berkeley GW is an open source code that can be used in conjunction with SIESTA. Deslippe, J., et al. “BerkeleyGW: A massively parallel computer package for the calculation of the quasiparticle and optical properties of materials and nanostructures.”, 2012, Computer Physics Communications, 183, 1269
The implementation of GW in SIESTA is one of the solutions that are under current development within the SIESTA-PRO project.