GW approximation is a well-known approximation for calculating exchange and correlation energies of molecular systems. However, the calculation is relatively computationally demanding, restricting the pure GW to small systems.
Further approximations can be made to alleviate the computational price, especially the memory requirements. The basis and implications of these approximations are discussed in the context of the calculation of energetic spectrum of sodium nanoclusters.
Stability and precision of different GW variants is discussed on several model calculations.