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Hi Dear

I use Lammps to calculate elastic constants of vinylester/titan nanocomposites. Because the matrix is polymeric, I’m forced to define the atom_style molecular.

I want to freeze the atoms of nanoparticle to prevent movement and interaction between them, But I meet following error:

“Fix freeze requires atom attribute torque”

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Hi Dear
I use Lammps to calculate elastic constants of vinylester/titan
nanocomposites. Because the matrix is polymeric, I'm forced to define the
atom_style molecular.

I frequently use "atom_style full", because it allows particles to
have charge, but if you don't need charge, "atom_style molecular"
should be fine.

I want to freeze the atoms of nanoparticle to prevent movement and
interaction between them, But I meet following error:
"Fix freeze requires atom attribute torque"

I think you do not need to use "fix freeze". According to the
documentation, use this only if you want to:

"Zero out the force and torque on a granular particle."
http://lammps.sandia.gov/doc/fix_freeze.html

(Granular particles are non-point-like particles such as "atom_style
sphere". You are using "atom_style molecule", so you should not use
this fix, unless for some reason you want to have large smooth round
particles in your simulation, which I don't think you wanted.)

  It's not clear from your post what you are trying to do.

If you want to immobilize some of the atoms in your simulation, then
the best way (I know of) to do this is to use the "group" command to
exclude them from the group of atoms you are moving with "fix nvt" or
"fix nve".
There are examples how to do this (and a discussion) here:

http://lammps.sandia.gov/threads/msg32451.html
http://lammps.sandia.gov/threads/msg32456.html

There are videos of some simulations using this approach here:

http://www.moltemplate.org/videos/nanotube+water/nanotube+water_t=0-285ps.avi
(NVT)

http://www.moltemplate.org/videos/translocation/walls+solvent+polymer_t=0-60ps.avi
(NPT)

and pictures here:

http://www.moltemplate.org/images/nanotube+water/nanotube+walls+water_side_pbc_t=305ps.jpg
http://www.moltemplate.org/images/nanotube+water/nanotube+walls+water_side_pbc_t=0ps.jpg
http://www.moltemplate.org/images/translocation/walls+solvent+polymer_t=0.jpg

Cheers

Andrew

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Oops, I just realized that Axel already responded to your question before I did.

Please avoid posting multiple copies of the same question to the
mailing list, if only because it makes it harder to reply.