fix the position of particle in rigid body

Dear all,

I would like to fix the position, or freeze the center particle in a rigid body, fixing the center of mass of the rigid body is also fine. The group of particles corresponding to the rigid body is tethered by a polymer chain.

First of all, I set the velocity to 0 and use fix setforce to set fx, fy and fz to 0 for the center particle, fix setforce comes after fix rigid. The velocity and force of the center particle are dumped, but I found the velocity isn’t 0 during the simulation, which means that it still moves.

Then I added “force N off off off” in fix rigid, same situation happens.

Are there some options in LAMMPS for it?

Thank you very much.

Best,

Bin

Dear all,

I would like to fix the position, or freeze the center particle in a rigid
body, fixing the center of mass of the rigid body is also fine. The group
of particles corresponding to the rigid body is tethered by a polymer chain.

First of all, I set the velocity to 0 and use fix setforce to set fx, fy
and fz to 0 for the center particle, fix setforce comes after fix rigid.
The velocity and force of the center particle are dumped, but I found the
velocity isn't 0 during the simulation, which means that it still moves.

Then I added "force N off off off" in fix rigid, same situation happens.

Are there some options in LAMMPS for it?

​if you do it correctly, it should work. so it seems to me, there is a
mistake in your input.

axel.​

Dear Axel,

I have attached the input and data files, the particles with id 11 and 34 are center particles in the two rigid bodies.

I would like to fix the center positions of the two rigid bodies and let them free to rotate.

It should be possible in LAMMPS, because I also tried another system, in which the two rigid bodies were replaced by two single particles, and they can be frozen.

Thanks a lot.

Regards,

Bin

in.lammps (1.14 KB)

data.lammps (19.7 KB)

Dear Axel,

I have attached the input and data files, the particles with id 11 and 34
are center particles in the two rigid bodies.
I would like to fix the center positions of the two rigid bodies and let
them free to rotate.
It should be possible in LAMMPS, because I also tried another system, in
which the two rigid bodies were replaced by two single particles, and they
can be frozen.

the force option in fix rigid works for me as it is described in the
documentation. please note, that your fix rigid command only requests
turning off of the center of mass translation for the second rigid object.
you have to enter a second force option with the index 1 to do the same for
the first rigid object. there is no need to use fix setforce here.

axel.

Hi Axel,

sorry I misunderstood the manual about the force option in rigid body, I thought the number 2 which I used meant that both the two rigid bodies.

It works now.

Thank you for your help.

\Bin