Author Topic: qsGW vs evGW convergence  (Read 135 times)

martijn

  • Full Member
  • ***
  • Posts: 49
  • Karma: +0/-0
qsGW vs evGW convergence
« on: April 21, 2021, 11:11:30 AM »
Hi,

I have observed that qsGW needs typically many more (10+) iterations than qsGW (3-4) in order to converge. Is that to be expected?

Thanks,

Martijn

chris.hol

  • Jr. Member
  • **
  • Posts: 16
  • Karma: +1/-0
Re: qsGW vs evGW convergence
« Reply #1 on: April 22, 2021, 11:55:07 PM »
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


martijn

  • Full Member
  • ***
  • Posts: 49
  • Karma: +0/-0
Re: qsGW vs evGW convergence
« Reply #2 on: April 23, 2021, 10:45:55 AM »
Thanks Christof