TOTAL-FORCE all zero

[yingma]

Hi all,

I was running a geometrical relaxation for a crystal with antifluoride structure. However, the run finished within one step, and thus the ionic positions did not change at all. I looked at the TOTAL-FORCE in OUTCAR and they are all zero, even for the very first configuration. Since the forces are all zero, vasp stopped the optimization. Then I tried to decrease the lattice constant by half such that it is way off the experimental value and run VASP again. The same thing happened, all the forces are zero and VASP stopped after the first step. I though this might be due to the symmetry such that all the forces cancel out exactly, so I tried one with ISYM=0. Again, all the forces are zero.

I never seen this before. Is this possible at all? Please help.

Thanks.

[admin]

1. If atomic positions are highly symmetric change the position of some
atom a little bit. This will cause that forces appear.
2. One do not need to relax highly symmetric positions.

[yingma]

I see. Thank you admin!