Relaxation of atoms in fixed lattice

LAMMPS LAMMPS General Discussion
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1

Hi everyone,

I did a full structure relaxation of a rocksalt structure in LAMMPS using the following code:

fix 1 all box/relax iso 0.0 vmax 0.001
thermo 100
thermo_style custom step pe press pxx pyy pzz lx ly lz
minimize 1.0e-24 1.0e-24 100000 100000
unfix 1

Now I wanted to keep this lattice vectors fixed (obtained from previous step) and relax the structure with small perturbations to the atoms. So is it possible to relax the atom positions while keeping the lattice fixed in LAMMPS?

Thanks
Dominic

2

What do you mean by “keeping the lattice fixed”?

3

Thanks for the response!

By “keeping the lattice fixed,” I meant keeping the simulation cell (lattice vectors, box dimensions, and angles) constant — i.e., not allowing any changes to the box shape or volume during the relaxation.

Essentially, I want to do what ISIF = 2 does in VASP: relax the atomic positions only, while the lattice parameters remain fixed at the values obtained from a previous full relaxation.

4

Just don’t use fix box/relax. Then the box will remain unchanged.

I don’t know anything about VASP syntax. I never used it.

1 Like
5

When using the minimize command, LAMMPS stops when either the energy tolerance (etol) or the force tolerance (ftol) is reached.

Is there a way to make it stop only when both the energy and force tolerances are satisfied?

6

Please post new questions as new topic with a suitable subject line. That will make it easier to others to look up the answer if they come across the same issue.