Since I have started working on monolayers I was using the
ISIF=3 tag for relaxation, this was after recompiling VASP with the modified "
constr_cell_relax.F" file. There was no problem in relaxing pure materials, but with the doping of 4x4x1 supercells I don't get convergence in relaxation and the calculations are taking too too much time.
On the other hand my friend is using the tag
ISIF=4 and he is getting always converged results.
Now I am a little bit confused with which tag should be used, since I think that because of vacuum along the c axis there should be no relaxation along it, so
ISIF=4 tag shouldn't be used. I want to know your opinions, especially if you have worked on relaxing doped monolayers.