# HOW to compute the shear force add on the system

Dear LAMMPS users:
I just looked up the 3d metal shear script in the LAMMPS website. It set the boundary forces all zero :fix 2 boundary setforce 0.0 0.0 0.0 , and then gave them a constant velocity to simulate shear movement. However, in the way ,you couldn’t get the information of the shear force add on the system , cause the force had been set to zero.

I try to use " fix rigid " comment to fixed the boundary , and give them a constant velocity , then add up all the shear direction forces on atoms . BUT I don’t know if that value is the accurate value of shear force. Cause i couldn’t find enough information in the manual about “forces on atoms”(fx fy fz ) , such as its formula or other something

Dear LAMMPS users:
I just looked up the 3d metal shear script in the LAMMPS
website. It set the boundary forces all zero :fix 2 boundary setforce 0.0
0.0 0.0 , and then gave them a constant velocity to simulate shear movement.
However, in the way ,you couldn't get the information of the shear force add
on the system , cause the force had been set to zero.

please re-read the documentation of fix setforce and look a bit more
carefully at the very last paragraph.

OK, I notice it.

the global quantities should be output by the thermo_style_custom command, But what the keyword should i use to output the 3-vector of forces by the thermo_style_custom command ?

OK, I notice it.‍

the global quantities should be output by the thermo_style_custom command,
But what the keyword should i use to output the 3-vector of forces by ‍the
thermo_style_custom command ?‍‍

http://lammps.sandia.gov/doc/Section_howto.html#howto_15

compute group/group & fix ave/time Is it right?

compute group/group & fix ave/time Is it right?

no.

FIX setforce contain 3 vectors itself , and output them as global quantities?

FIX setforce contain 3 vectors itself , and output them as global
quantities?

one vector with 3 values. the force vector that it wiped out.