Reg: Rigid Movement of a group

Hello Lammps users,

Is it possible to rigidly move a particular group of atoms along with another group during minimisation, while the force components of the group to be rigidly moved being zero.

I tried the fix setforce command but the it freezes the group displacement as well, during minimisation.

Thanks in advance,

Cheers,

Srinivasan

Hello Lammps users,

Is it possible to rigidly move a particular group of atoms along with
another group during minimisation, while the force components of the group
to be rigidly moved being zero.

it doesn't make sense to move *during* a minimization, since there is
no such thing as a "timeline" and thus no way to determine at which
speed those movements would be meaningful. however, what is usually
done in similar cases, is to alternate between moving the group(s) of
atoms and running a minimization. LAMMPS supports this via the
displace_atoms command and its looping constructs.

axel.

Dear Mr.Kohlmeyer,

I can understand your point, since there is no timestep in the minimisation procedure it is not possible.

But my criteria is like this I am trying to implement a pair style for core/shell model to model Olivine, for which I first implemented arrays to store shell properties parallel to core’s and did the rigid movement of shells, but the procedure gets complicated for using different features of lammps.

So now I tried to give shell as a n+1 th atom type and tried to rigidly move the shell along with it’s core(since the shell is massless) during the energy minimisation of the cores.

Once if I could do the rigid movement of the shells along the core, I could do the shell minimisation by using the fix setforce command where the core atoms has to be constrained.

Sorry if I am wrong, since I am a beginner.

Thanks in advance,

With regards,

Srinivasan Mahendran

Dear Mr.Kohlmeyer,

I can understand your point, since there is no timestep in the minimisation
procedure it is not possible.

But my criteria is like this I am trying to implement a pair style for
core/shell model to model Olivine, for which I first implemented arrays to
store shell properties parallel to core's and did the rigid movement of
shells, but the procedure gets complicated for using different features of
lammps.

the fact that you cannot think of an alternative, still doesn't mean
that what you are asking for is meaningful (it isn't).

So now I tried to give shell as a n+1 th atom type and tried to rigidly move
the shell along with it's core(since the shell is massless) during the
energy minimisation of the cores.

Once if I could do the rigid movement of the shells along the core, I could
do the shell minimisation by using the fix setforce command where the core
atoms has to be constrained.

Sorry if I am wrong, since I am a beginner.

what you need to do is to write a different integrator/minimizer then
that takes care of the additional constraints the way you want them to
be taken care of.

axel.

Yes, I accept it. I have one modified linesearch algorithm implemented, but I will try to write an alternative minimiser/integrator.

Sri