thanks for your answer.

sorry for my trivial question.

yes. but i don’t know how to do it in lammps?

which command should i use?

Best

thanks for your answer.

sorry for my trivial question.

yes. but i don't know how to do it in lammps?

yet, that is the wrong approach. before looking into what command exactly

would be needed in LAMMPS, you need to understand, how adding a force

through using fix addforce will change the force between two groups.

which command should i use?

start with a piece of paper and a pencil. make some simplified model and

start thinking!

depending on your system and your specific fix addforce command, you may be

able to fully pre-compute the impact of fix addforce. you may even find

that it has no impact at all. like i said previously, this all comes down

to a little bit of vector algebra.

axel.