Hi LAMMPS users,

I am trying to compute the friction force between two surfaces whose interactions are defined by the Tersoff potential. In the LAMMPS documentation, it says that the compute group/group command cannot accurately describe forces between two groups with 3-body and other many-body potentials.

I think I can accomplish the same thing using the “variable group fcm()” or “compute reduce fx” commands. Do the forces calculated by these commands have the same restrictions on 3-body and many-body potentials? If so, is there a better way to calculate the forces between two Tersoff surfaces?

Thanks,

Michael

Hi LAMMPS users,

I am trying to compute the friction force between two surfaces whose

interactions are defined by the Tersoff potential. In the LAMMPS

documentation, it says that the compute group/group command cannot

accurately describe forces between two groups with 3-body and other

many-body potentials.

true. because compute group/group loops over all pairs of atoms

between those two groups and computes the individual (pairwise)

interactions and sums them up. so that won't work with manybody

potentials.

I think I can accomplish the same thing using the "variable group fcm()" or

"compute reduce fx" commands.

i think so, too.

Do the forces calculated by these commands

have the same restrictions on 3-body and many-body potentials?

no. this is just taking the forces on the individual atoms and sums

them up. if this would not work, you could not use a manybody

potential in LAMMPS at all.

axel.