Dear all,
when i saw a tension case in the lammps website, i found that atoms in upper and lower groups which were named gbhigh and ghlow were fixed at first, then they were moved through displace_box(change_box in current lammps) command to stretch a system. could you please tell me how to compute the forces between the boundary (gbhigh or gblow) and the middle part. thank you so much.
Best Regards,
Liu
Dear all,
when i saw a tension case in the lammps website, i found that atoms
in upper and lower groups which were named gbhigh and ghlow were fixed at
first, then they were moved through displace_box(change_box in current
lammps) command to stretch a system. could you please tell me how to
compute the forces between the boundary (gbhigh or gblow) and the middle
part. thank you so much.
using compute reduce with the sum operation on atomic forces of the atoms
in either group should give you the net force that you are looking for
(assuming there is nothing else in the system and no periodic boundaries in
the stretch direction).
for more complex cases, you may also use compute group/group, but that has
some restrictions in the choice of potentials.
axel.
Thank you so much.
But when i computed the forces of atoms in the boundary groups which were fixed by the “fix 1 boundary setforce 0 0 0” command, the values of the forces are 0. Does it mean that there’s no force acting on the boundary atoms by the middle part?
There is a fix store/force command which stores forces
on atoms before additional fixes are applied, like setforce.
If you compute reduce on those stored forces, or dump them,
they will be non-zero.
Steve