I would like some suggestions on how to do structural relaxation (while I'm at it, let me list some synonyms for search exposure - geometry optimization, structural refinement, energy minimization etc) using molecular mechanics (force fields) that preserves space group symmetry.
A typical workflow that I'm thinking of is to start by generating a structure data file (eg. cif, but later easily converted to input data for various packages) with a reasonable crystalline arrangement of atoms, usually <1000 in number and having some spatial symmetry higher than P1. Then I would refine the structures with atomistic simulations at various levels of accuracy (ranging from mol mech to DFT on a HPC cluster if need be) until they compare reasonably with experimental data which I already have for similar structures, in which one of the elements is substituted with another in the same group on the periodic table.
I have so far tried using LAMMPS, GROMACS, Forcite (a module in Materials Studio) and was able to put together bare minimal input files for each of their structural relaxation routines, without spending too much time going through their thick manuals to see if they have the exact options/functions that I need. Under default settings (with say, the DREIDING force field), they all seemed to break initial symmetries, maybe because of some thermostat that causes random displacements.
But I feel that the need for this kind of (symmetry-respecting relaxation) task at low level is fairly common and there's gotta be some standard, straightforward way to do this on an ordinary desktop workstation. I know that DFT packages like Quantum Espresso or VASP do this kind of relaxation by default, mainly because thermostats aren't part of their standard routines.
Can anyone save me some web-searching/manual-reading time by pointing me to the right direction/tool?
(This question may very well boil down to asking how to turn off the thermostat...)
Thanks in advance