I run a MD simulation for a confined shear model using REAX force field. I used to use compute group/group to evaluate the friction force (Fxz) which induced by lubricant on a surface. However, this compute command is only applicable for pairwise interactions such as LJ, Buckingham, Morse … potentials.

I have carried out a comparison between the shear tress evaluated by Txz = Fxz/Surface area with Sxz , but Sxz is different with Txz.

Does anyone have any good approach the evaluate the shear stress/friction force for confined shear model using REAX force field ?

Best regards,

Thi Dinh TA

Associate Research Fellow

School of Mechanical, Materials & Mechatronic Engineering

I run a MD simulation for a confined shear model using REAX force field. I
used to use compute group/group to evaluate the friction force (Fxz) which
induced by lubricant on a surface. However, this compute command is only
applicable for pairwise interactions such as LJ, Buckingham, Morse ..
potentials.

I have carried out a comparison between the shear tress evaluated by Txz =
Fxz/Surface area with Sxz , but Sxz is different with Txz.

Does anyone have any good approach the evaluate the shear stress/friction
force for confined shear model using REAX force field ?

not directly, but i recall that there were discussions in the past
about different approaches to derive stress for different potentials.
you may want to try and dig (deep?) into the lammps-users mailing list
archives and see if there is anything helpful among the papers
mentioned in those discussions.

Here the shear stress and normal force acting on the slabs are output from fix aveforce and fix setforce. Assuming that you use these to apply the pressure (i.e. push one slab down and keep other fixed), this should work for any pair style.