Despite its accuracy, the GW approximation has some limitations. It is computationally expensive, making it challenging to apply to very large systems or complex materials. Additionally, the accuracy of the GW method depends on the initial guess for the Green's function, typically derived from DFT, which can sometimes lead to convergence issues. Moreover, the GW approximation may not fully capture all correlation effects, necessitating the use of more advanced methods like the Bethe-Salpeter equation for excited states.
