I have a large disordered cubic structure that I would like to do AIMD on to look at cation diffusion. I found the primitive cell and then ordered it to create several configurations. I will then relax each one and select the lowest energy configuration for AIMD. But first I have to relax the structures.
Ordering the cell will naturally decrease the symmetry of the structure to something like tetragonal or monoclinic. Typically for a calculation in VASP we switch symmetry on (
ISYM=2). In this case, VASP detects tetragonal symmetry and forces the lattice parameters to fit those symmetry constraints, which is incorrect because I know the structure is cubic.
So my first question is: Is this okay? I presume it isn't.
If not: What's the best or correct way to deal with this? Just setting
ISYM=0 or -1?
Or is it better to constrain the cell shape with
ISIF=2? Or maybe both?
I was under the impression that the structure needs to be fully relaxed before doing AIMD: So then setting
ISIF=2 would not be correct?