Results changes with domain size for oriented crystal

Dear lammps users,

I want to deform oriented single crystal copper by using the following command:

lattice fcc 3.61 orient x 1 1 1 orient 1 -1 0 orient z 1 1 -2

After performing NPT, the triaxial deformation is applied using the following command:

fix 2 all deform 1000 x erate 0.005 y erate 0.005 z erate 0.005

But when I see pressure-time curve, then I found that the shape of the pressure-time curve is
changing with the increase in domain size. I have varied number of atoms from 10^5 to 1.28 x10^8 atoms.

Can anyone pls suggest me what I am doing wrong? I would like to appreciate your help in this regard.

Thanks in advance.

With best regards,

Not enough information to say much.
Have you verified, e.g. by viz, that
the 2 systems are "identical", i.e.
that they have deformed with the same
strain and that the bounaries of
the box with an oriented lattice have
the correct periodicity?