[lammps-users] Vibration simulation

Dear all,

I am attempting to simulate flexural vibration of a Si nano-cantilever beam. To provide an intial displacement at the free end of the beam, I used displace_atoms command for a group of atoms at that end, while the other end is kept fixed using fix setforce … 0 0 0 , and let the system respond to this initial condition. What I see is that only the group of atoms suddenly get displaced, as if the group gets broken from the rest of the beam.

But since my idea was to provide an intial condition such that max disp is at the free end and it curves to zero at the fixed end, so I used variable to define the displacement with respect to coordinate x[] corresponding to each atom, and then give this as input to displace atoms command. There seems to be errors with regards to inter processor communication when I do this.

Can anyone suggest a suitable command or fix to initiate the system response? Alternately, is there a procedure to incorporate a similar velocity boundary condition.

Finally, does fix_wiggle induce a forced vibration?

Thanks, Ganesh


You can't give a variable to displace_atoms and expect it to
do what you describe below - the command doesn't do that.

I would create your own data file for input to LAMMPS that puts
each atom where you want it, as an initial condition.

Yes, fix wiggle forces some atoms to oscillate.