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Re: [lammps-users] Rigid body breaking
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Re: [lammps-users] Rigid body breaking

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Tue, 19 Dec 2017 09:50:45 -0500

on top of that, applying two time integration fixes (both, fix move and fix rigid do time integration) to the same atoms is almost always and this case a definite error. LAMMPS must have printed a warning and these warnings need to be taken seriously unless you know for a fact, that they don't apply your specific case.


On Tue, Dec 19, 2017 at 8:17 AM, Stefan Paquay <stefanpaquay@...24...> wrote:
This is incorrect. If you remove the wall from the time integration fix, they will not move due to forces on them, but their forces on the polymer will still be included in the equations of motion on the polymers. The approach I suggest is also mentioned in the docs of fix rigid. 

On Dec 19, 2017 12:59 PM, "Mohd Ibrahim" <mihph12@...24...> wrote:
Thank you very much for your response. 
If I remove the wall atoms from time integration, the polymer chains wouldn't see the wall atoms hence the movement of wall will not cause  shearing of the polymer chains confined between the walls. 

On Tue, Dec 19, 2017 at 4:28 PM, Stefan Paquay <stefanpaquay@...24...> wrote:
Not directly an answer to your question but I think you might be overcomplicating things.
Why don't you just remove your wall atoms from the time integration and just move them with a fix move? That will make things considerably easier and might magically make your current problem go away, or at least easier to address.

On Tue, Dec 19, 2017 at 7:39 AM, Mohd Ibrahim <mihph12@...24...> wrote:
Dear LAMMPS developers,
                                   I have a polymer system confined between two crystalline walls. The wall atoms are assigned as rigid body. Force and torque on both the walls is set to zero. The interaction among wall atoms is switched off. 
In order to calculate viscosity I shear the system by moving one of the wall while keeping the other wall fixed. I used a fix move command to do so. But after some time the moving wall is deforming and breaking apart although force and torque on it due to other particles in the system is set to zero and the wall atoms don't interact among each other. 
I would be much grateful if any one could help. Here is the part of input script where it is breaking apart. 
velocity wal_lo set 0 0 0 units box
fix 24 wal setforce 0.0 0.0 0.0
fix 26 wal  rigid/nvt group 2 wal_hi wal_lo temp 1.0 1.0 0.1 force * off off off torque * off off off
fix        6 wal_hi move linear 1 0 0 units box
dump            21 all custom 5000 eq_shear.lammpstrj id mol type xu yu zu vx vy vz 
dump            27 poly custom 5000 eq_shear_poly.lammpstrj id mol type xu yu zu vx vy vz 
restart 5000000 shear
run 5000000
The wal group  contains both wal_lo and wal_hi
Thank You ,

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Dr. Axel Kohlmeyer  akohlmey@...12...24...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.