[lammps-users] question about "fix deposit"

Thank Steve and Axel.

I want to simulate the material growth. Does the nve system properly describe the experimental system? Is it also bad choice by using NVP, NPT in system with changing atom numbers?

nve is a good choice. i would first equilibrate the substrate and then
run nve. the only effect that you would be missing is the exchange of
kinetic energy with the bulk of the substrate. this could be handled by
using fix langevin on a few (additional) substrate layers near the bottom.
but with every deposited layer, this will become less important.

I have now chosen nve + langevin. The command is
fix 1 substrate nve
fix 2 substrate langevin 1800.0 1800.0 100.0 48279 scale 3 1.5

are you sure about the "scale 3 1.5" addition?
please check the manual for its meaning.
your whole substrate is thermalized to 1800K?
in any case, see my suggestions above.

However,there is still an error making me crazy :" ERROR: Illegal fix langevin command". I am sure the command line is right in fix langevin, and I do not know the reason for this error.

how current is your version of lammps?
also, please check carefully all numbers.
unless you are using the C locale (i.e. plain 7-bit ASCII characters),
it is possible that you add characters, e.g. decimal points, that are
not recognized as that. i've seen this happen particularly often when
people write input files on a windows machine with a foreign character set.