How could I generate the parameter of 'selective dynamics' in POSCAR with ASE?

Question

I often use selective dynamics to do structure optimization in VASP, but I am not sure how to do it when using ASE, it seems I could use the constraint class to tell ASE what I want to do. My question is:
When I use the constraint class, does ASE generate the POSCAR that includes the selective dynamics parameter? Or it is like the case of optimizer, ASE could just use VASP as a calculator, and set the constraint outside the loop of VASP calculation?

Answer 1

The FixAtoms constraint will be turned into the selective dynamics tags as "F F F". ASE will also convert selective dynamics to this constraint when reading.

I think the FixedPlane and FixedLine could in theory also work, but I am not sure they do since they support directions not aligned with the X, Y, and Z axis. If you need this and it doesn't work (just give it a try), you might ask on the ASE Matrix chat to see if someone is willing to add it for you or tell you how to change it yourself.