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Hi,

I wrote a little AWK script that reads direct lattice parameters from OUTCAR and uses that in combination with XDATCAR to build a xyz trajectory file, so I can view the geometry optimization with ISIF=3 (optimize cell & ions)

Not all ISIF=3 runs seem to change the cell in between the iterations. When does VASP decide to change these parameters and when not?

(I checked ISIF=3 and NSW=large_enough in the OUTCAR file. It gives cell parameters twice in the beginning of the file and not there-after)

thanks, Lambert

1) The criterion for changing geometries is controlled by the
EDIFFG input parameter
EDIFFG > 0 changes in the total energy between 2 subsequent ionic steps
EDIFFG < 0 maximum remining forces and the total stress
have to be smaller than the | EDIFFG |
as a breaking condition for the ionic / geometry optimization steps.