Hi,
indeed this is to be expected; qsGW will in general need many more iterations than evGW and sometimes even more than HF/DFT calculations. qsGW updates all the Fock-Matrix elements, making a re-diagonalization of the Fock-Matrix necessary in every iteration. Especially in cases were the self-energy has peaks close to the Fock-Matrix elements a steep dependence of the latter to small changes can be expected. This leads to a rather slow convergence, and DIIS is not helping too much in these cases. In evGW only the eigenvalues/quasiparticle energies but not the eigenvectors of the Fock-Matrix are updated, a re-diagonalization is not needed. Therefore, it converges pretty fast especially with DIIS.
All the best,
CHristof
