[lammps-users] Forces on an indenter

Hi all,
I would like to know the forces for an indentation problem. The documentation says that while using the fix indent command, a 3-vector of the forces on the indenter is produced, and a scalar for the energy of interaction. I would have 2 questions about it:

  1. I read that the energy is simply the sum of the interactions atom/indenter potential. Now what about the forces? I am pretty curious about the way it is calculated. Is the indenter assimilated as a “real” physical object on which the atoms are pushing?

  2. I have some difficulties to print this vector. I can get the scalar for the interaction energy, but the components of the vector remain 0, which doesn’t make sense to me. I am running a relaxation process around the indenter, and here are the command I’ve been using:

fix ball all indent 10 sphere 0.0 0.0 -40 10.0 units box
fix_modify ball energy yes

thermo 20
thermo_style custom step f_ball f_ball[1] f_ball[2] f_ball[3]
minimize 1.0e-12 20000 500000

Thanks a lot.

your Qs

1) yes, its force on the indenter as if it were an object. See the code
in fix_indent.cpp::post_force() for how force is computed. It's a simple

2) See examples/indent/in.indent.min. If you add your thermo_style custom
command to it, it will print out the eng and forces on the indenter. Note
that the 2Aug08 patch updated the in.indent.min file so that the syntax
of the minimize command matches the current version.