Box dimension in lj and real units

Dear LAMMPS users,

I have a small doubt about box dimension in lj unit.
I am doing polymer simulation inside the box dimension of -5 to 5 in all x y z direction with periodic boundary condition.
When i do above things with real and lj units with appropriate conversion then the properties like end to end distance, radius of gyration and mean square displacement are same.
But when i do the same things with much larger box size -500 to 500 in all x y z direction so that atoms don’t need periodic boundary condition. The end to end distance and MSD values are different between lj and real unit.

According to theory end to end distance, mean square displacement should be independent of box dimension.
In real units it seems to be true but for lj units its not.
I don’t know why?

Thank you.

Ankit Agrawal
Institute of Mathematical Sciences
Computational Biology

You can do an identical simulation in any units (not with round-off effects,
but statistically). You can convince yourself of this by setting
up two input scripts, in different units, and seeing that for a few
time steps you get identical outputs. You can do this for either
your small or large problem.