[lammps-users] group force calculation for AIREBO

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1

Hello,

I am running a simulation to simulate the depression of a membrane. I want to get force vs. displacement data for a group (all groups use the same AIREBO potential), but I have difficulty calculating the force. Here is how I have tried to calculate force:

  1. compute stress/atom, with a reduce to sum and average and divide by the “volume” of the group of atoms I am interested in. My main problem here is the volume calculation. The forces reported by this method seem to be off (by orders of magnitude), I estimate the volume of the group by taking the volume of the entire ensemble (vol), and multiplying it by a factor that corresponds to the portion of the space occupied by the group I am interested in. It should be noted that I have shrinkwrap boundary conditions, so I believe my simulation box is growing with the membrane as it deforms.

  2. compute group/group, does not work with AIREBO- is there any way to get it to work? Is there an analogous method?

Any suggestions are welcome. Thank you,

-Emil

2

If you want the force on the membrane due to all the other
atoms (the indenter?), just use compute reduce to
sum the forces on atoms in the membrane group.
Forces between membrane atoms will not contribute (they
should sum to zero).

Steve

3

No further ideas - you can always check if you did this
correctly by dumping per-atom forces into the dump file
and summing them yourself.

Steve