# [lammps-users] computation of force

hello steve:
I made a nano-cutting simulation with diamand tool and si workpiece. I wanted to output the cutting force of the non-rigid tool. the tool’s radius was 1.57nm. I output fx, fy, fz by fix_setforce command at the beginning of the simulation, but all the sum of each value were large .
the command
fix fix_boundary_tool boundary_tool setforce 0 0 0
sum of fx=-1132.8022 sum of fy = -1392.6003 sum of fz = -89.41491.
If I change the tool to be rigid by fix_setforce command.
fix fix_tool tool setforce 0 0 0.
the results is very small
-7.51620e-13 7.609468e-13 1.003972 e-12.

I go through the manual and find the compute_group/group command. It can compute force between two different groups. I use the tersoff potential and find the potential must be pairwise interation. I keep the tersoff potential between si-si and c-c and change the potential between Si and C to be morse . but there is an error
Pair style does not support compute group/group.
pair_style hybrid morse 7.5 tersoff
pair_coeff * * tersoff SiC.tersoff Si Si Si C C C
pair_coeff 13 46 morse 0.435 4.6487 1.9475

I want to know whether the morse potential not to be applied to the group/group command.

so I want to know that which command I should select to compute the cutting force that workpiece exert to tool if the tool is non-rigid.

in.sic (4.53 KB)

I made a nano-cutting simulation with diamand tool and si workpiece.
I wanted to output the cutting force of the non-rigid tool. the tool's
radius was 1.57nm. I output fx, fy, fz by fix_setforce command at the
beginning of the simulation, but all the sum of each value were large .
the command
fix fix_boundary_tool boundary_tool setforce 0 0 0
sum of fx=-1132.8022 sum of fy = -1392.6003 sum of fz = -89.41491.

Why do you think this answer is wrong?

Steve

2009/9/19 王治国 <[email protected]...>: