how to remove sepecific atom out of the box

Dear All:
i am doing the ion bombardment work with lammps.Now i want to remove the ion when the ion reach a location of the substrate ,so that i can reduce my simulation size.Can anyone tell me if lammps have such commands ?How do i achieve this goal? Best regards.

Dear All:
         i am doing the ion bombardment work with lammps.Now i want to
remove the ion when the ion reach a location of the substrate ,so that i
can reduce my simulation size.Can anyone tell me if lammps have such
commands ?How do i achieve this goal? Best regards.

i am quite certain what exactly the problem is. you have to provide
more details of your simulation setup and why the "simulation size"
matters.

to delete a single atoms, you can create a group containing that atom
and then use the delete_atoms command.

axel.

Sorry,I will tell in detail next.
I am doing the successive 30keV gallium ion bombardment of silicon,perhaps 500 ions in total.The gallium with the 30keV energy will deposit all the energy to the silicon target if the target thickness is 30 nm or higher according to the theoretical analysis.So in this simulation,the simulation size matters very much because of the computational limitations.Now for my simulation,I want to have a simplification.That is to say I plan to have a target which the thickness is lower than 30 nm,for instance 15 nm.Then in the bombardment simulation with lammps,I want to tracking the gallium.And when it approves the botttom of the target(2.5 nm above the bottom),I remove this ion or turn off the ion."Turn off"means the ion has no velocity and no interaction with other particles.I am intersted in the initial stage of the ion bombardment ,so I want to have this simplification.But the problem is that in lammps how can I remove or "turn off "the ion when it reach the target location. Best regards.

Sorry,I will tell in detail next.
I am doing the successive 30keV gallium ion bombardment of silicon,perhaps
500 ions in total.The gallium with the 30keV energy will deposit all the
energy to the silicon target if the target thickness is 30 nm or higher
according to the theoretical analysis.So in this simulation,the simulation
size matters very much because of the computational limitations.Now for my
simulation,I want to have a simplification.That is to say I plan to have a
target which the thickness is lower than 30 nm,for instance 15 nm.Then in
the bombardment simulation with lammps,I want to tracking the gallium.And
when it approves the botttom of the target(2.5 nm above the bottom),I remove
this ion or turn off the ion."Turn off"means the ion has no velocity and no
interaction with other particles.I am intersted in the initial stage of the
ion bombardment ,so I want to have this simplification.But the problem is
that in lammps how can I remove or "turn off "the ion when it reach the
target location. Best regards.

the simplest way to handle this would be to just let those gallium
atoms pass through the silicon slab and drop them from the simulation
after that.
this can be achieved by having a fixed boundary below the bottom of
your slab then then use "thermo_modify lost ignore". once atoms move
outside the box boundary, they will be "lost" at the next update of
the neighbor lists, and you can tell LAMMPS with thermo_modify to
ignore that fact.

axel.