center of mass2

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1

Hi all

In my simulation system there are two immisible liquid phases, one of them is in the right side of the simulation box and the other is in the left side in Z direction. In X and Y direction center of mass velocity is 10^-5 in read units and in Z direction the velocity is about 10^-4. Visually I see displacement of phase 1 by phase 2 periodically. I used periodic boundary conditions but I think after equilibration I should not see the displacement. Would you please help me about this?

Would you please give an attention: In equilibration step I used NVT that there is not the above phenomena but in production step that I used NPT there is the above phenomena.

Thanks alot for your time an d attention.

Best Regards

Maria

2

Hi all

In my simulation system there are two immisible liquid phases, one of them
is in the right side of the simulation box and the other is in the left side
in Z direction. In X and Y direction center of mass velocity is 10^-5 in
read units and in Z direction the velocity is about 10^-4. Visually I see
displacement of phase 1 by phase 2 periodically. I used periodic boundary
conditions but I think after equilibration I should not see the
displacement. Would you please help me about this?

do you remove the center of mass momentum of either both phases
or the entire system at the beginning of the production run?

axel.

3

Hi

How can I do this?

Only in my equilibration step I generate initial velocity of atoms by the following command:

velocity all create 298.0 12345678 mom yes rot yes dist gaussian

Regards

Maria

4

Hi

How can I do this?

Only in my equilibration step I generate initial velocity of atoms by the
following command:

velocity all create 298.0 12345678 mom yes rot yes dist gaussian

try:

velocity all zero linear

before starting production.

http://lammps.sandia.gov/doc/velocity.html

if you still have momentum buildup,
you can try using fix momentum, but
that has to be used with great care in
multi-phase systems, to not make a
mess (e.g. try using it on each phase
separately, and don't use it too frequent).

cheers,
     axel.