What is the best way to take a rigid surface in the initial position??

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1

Dear all

I want to take my rigid surface in the initial coordinate position, I have used the fix recenter command, However the surface is moving and changing position.

Could any one mention me what is the best way to do this?

Thanks in advance

2

Dear all

I want to take my rigid surface in the initial coordinate position, I have
used the fix recenter command, However the surface is moving and changing
position.

Could any one mention me what is the best way to do this?

​the easiest way to immobilize atoms is to not apply time integration to
them.

axel.​

3

Dear Axel

In my system I have two phase, one is gas and another is solid surface. my simulation condition is NVT at 273K. I made some of the efforts

  1. I make have considered my gas as a group and fix nvt at 273K for them and to avoid time integration of surface I did not do anything with this. Therefore, the system temperature is increasing at (190K average) during the simulation. Furthermore, since the surface is out of time integration then could it show the interaction due to the VDW attraction?

  2. I tried with a different way, I make a different group with the edge atom of the surface then apply move linear command for them and recenter for the group which one contain rest of the atoms of surface. In that case I also found that the temperature change is similar to point 1.

  3. I tried to fix the position of the surface with only set force command but in that case the position is changing but after some time step its fixed in a position.

I am not sure what wrong I did. Could you please suggest any information.

Thanks in advance

4

Dear Axel

In my system I have two phase, one is gas and another is solid surface. my
simulation condition is NVT at 273K. I made some of the efforts

1. I make have considered my gas as a group and fix nvt at 273K for them
and to avoid time integration of surface I did not do anything with this.
Therefore, the system temperature is increasing at (190K average) during
the simulation.

​what is the temperature of a system, where some atoms are thermostatted to
a given temperature and some are kept "frozen"?​

Furthermore, since the surface is out of time integration then could it

show the interaction due to the VDW attraction?

​force computation is independent of time integration. do a visualization
of your simulation and see for yourself.​

2. I tried with a different way, I make a different group with the edge
atom of the surface then apply move linear command for them and recenter
for the group which one contain rest of the atoms of surface. In that case
I also found that the temperature change is similar to point 1.

​these are meaningless choices, however, you may - by chance - run into a
similar situation as before.​ thus you need to answer the same question i
posed before again.

3. I tried to fix the position of the surface with only set force command
but in that case the position is changing but after some time step its
fixed in a position.

​what is the point of asking for advice and then ignoring the advice you
received and doing something else?
the questions you are asking have been asked and answered a great many​
times. you will find the discussions in the LAMMPS mailing list archives.
have a look for yourself.

I am not sure what wrong I did. Could you please suggest any information.

​i already gave you good suggestions​. however, i cannot help you, if you
don't understand them.

axel.

5

Dear Axel

Sorry for extended try and thank you for your suggestions.

Certainly the temperature will be decrease if some of the atoms have given temperature and some are frozen, However, since the temperature calculation is a time integration calculation then how could I apply temperature to my surface by avoiding time integration ?

Please help I am trying to understand you

Thanks in advance

6

Dear Axel

Sorry for extended try and thank you for your suggestions.

Certainly the temperature will be decrease if some of the atoms have given
temperature and some are frozen, However, since the temperature calculation
is a time integration calculation then how could I apply temperature to my
surface by avoiding time integration ?

​you asked for your surface atoms being immobile (or "rigid"). immobile
atoms have a temperature of 0K. that is what you can achieve by following
my suggestions. if you want your surface atoms to have a temperature, you
have to allow them to move​ as well.​ that is just basic physics. you
cannot have both at the same time.

axel.