Berkely GW

The G stands for the Green’s function while the W stands for the screened Couloumb interaction. The screening is encoded in the inverse dielectric function ${ϵ}^{-1}$.

Finding the inverse dielectric function

Calculate plane-waves matrix elements (FFT’s) $⟨{\psi }_{j,k+q}|e^{i(G+q)\cdot r}|{\psi }_{ak}⟩$