Sorry for misunderstanding if any. I need a method to adjust simulation box that can be used in “minimize” with no prerequisite as periodic boundary condition.
For Non-PBC, you have two choice, 1) still use PBC but with large vacuum at the ends so that the ends do not interact with each other. 2) use s or f BC. For the former case, to do static loading, you can use ‘fix deform’ command. For the latter case, “displace_box” command should be an option.
BTW, your name sounds familiar. Did you use to study at JHU and live in broadview apt?
If your boundaries aren't periodic, I don't know what it means to adjust
the box size. If you want to minimize while adjusting a (periodic) box
then use the fix box/relax command.