I am trying to minimize a system of about 55 million atoms using conjugate gradient with 0.0 as energy tolerance and 1e-08 as the force tolerance. It is taking a lot many steps than expected. Can anybody tell me if there is any limit to the number of atoms for the minimization algorithm. I am checking the sum of fx^2+fy^2+fz^2 for all atoms at intervals of 20000 steps and this value is not changing at all. Any comments.