Related to Optimize Geometry

[Indra M]

In Optimize Geometry tool at QuantumATK, there is an option Lattice Constraints, which is having "Fix Lattice Vectors for  x   y   z" with check box for tick/untick. Can anyone suggest me what it actually means? Is it necessary to tick in all the dimensions during geometry optimization? Please suggest.

[Tue Gunst]

An optimization usually refers to adjusting (minimizing) the total energy by moving atoms.
Using the lattice constraint one does this for fixed lattice (existing unitcell whatever strain is present).
If you also want to adjust the unitcell by varying the strain while minimizing the total energy, then you don't need the lattice constraint.

[Indra M]

Thank you for your suggestion. If we tick in the checkboxes besides x, y, and z-direction, whether it will restrict the movement of atoms totally? or they can move freely within the lattice during Geometry Optimization?

[AsifShah]

The MOvement will be only within lattice. I guess it is like the box dimensions remain same but whatever is inside box rearranges