inquire of the periodic boundary coundition

Dear Producer

I am trying to do grain boundary simulation with periodic boundary conditions in 3D but I got a problem is that when I apply translation between the two grains, to make sure the two grain boundaries identical the boundaries in the perpendicular direction are shifted. Hence I need a shifted grain boundary condition. Could you please give me some suggestions on how to achieve this?

Best wishes,
Yaoshu Xie

Not sure what you mean by shifted BC. If you form a GB from a bicrystal, e.g. a simple tilt boundary,
the usual way to model it is either

a) periodic in all 3 dims, which means you are really simualting a system with 2 boundaries, i.e. ABABAB… in an infinite sense
b) non-perioidc boundaries in the perp direction, far enough from the boundary to not affect it