GW approximation

The GW approximation, often abbreviated as GW, is a method used in many-body physics and condensed matter theory to calculate the electronic properties of materials. It is particularly effective for studying the electronic structure and excitations of a system, such as the energy levels and optical properties of solids. **Key features of the GW approximation include:** 1. **Green's Function and Screened Coulomb Interaction**: The GW approach is based on the Green's function formalism.