Gravity not affecting particles inserted with create_atoms on a lattice

I have a small testing simulation where it attempts to drop a small block of particles onto a surface. The block is inserted with create_atoms using a lattice structure after the 1st timestep is run, but after they’re inserted they continue to hang in the air exactly where inserted as though the gravity fix isn’t affecting them.

Here’s the gravity fix command:

nobody can help you based on such terse information and moreover this
seems to be a LIGGGHTS input in the first place.

if you suspect that there is a problem with LAMMPS, please provide a
minimal but runnable input deck that can be run and that demonstrates
the problem. otherwise you will be only your own or have to get very,
very lucky.


Although your inpo info is far from complete looks like your fix gravity is acting on all atoms, block and surface. Any chance indeed they are all free falling?

From the gravity magnitude, I assume you are in si units.
How fast the particles will fall is a function of your time step
and the gravity magnitude. Typically they take many time steps
to fall. You can change those params and accelerate the
process for debugging. And you can dump the coords and
velocity and verity that they are moving.