How is the lattice fixed in lj?

rho* provided does the program change the number of atoms as to get the desired rho* or it scales something else. I have changed rho* but the total number of initialized atoms remain the same.
And when I change rho* to 2 the program give me an error saying atoms lost.

rho* is a function of # of atoms and volume. If you
use create_atoms with a create_box and region that
is scaled by the lattice size, then the code can put N
atoms in a smaller box to be a larger rho*. If you
make rho* large (e.g. 2) then atoms will overlap too
much and the system can blow up when you start


Thanks Steve. I also wanted to add that decreasing the size of time step was helping as well. As Steve mentioned, there might be an overlap and blow up of forces when density is large.