[lammps-users] box/relax under constant volume


Is it possible to affect an energy minimisation via the box/relax protocol with
the only constraint being that the volume be held fixed?

As far as I can see, the only options I can supply to "box/relax" are the off-
diagonal strains (xy, xz, yz) which leave the volume unchanged.

Can I also allow the box lengths (Lx, Ly, Lz) to vary, but such that:
Lx ྾ Ly ྾ Lz = V? This is called "pure shear", while the former is called
"simple shear". So what I'm asking is whether it is possible to allow the box
to relax with both these strains as degrees of freedom.

(Is spirit, this would be a conjugate to the "couple" keyword, since here, the
dimensions are in some sense "anti-coupled")


If it is not mentioned in the documentation, then it is not implemented.

It should not be too difficult to implement a volume (or area) constraint. For the most part it would be tedious to test for all allowed and disallowed combinations with the couple keyword settings.