Conventional design tools were not developed for designing square
zero-shift supercells. Conventionally, solutions that enable square
zero-shift supercells were found by trial and error or by exhaustive
analysis. According to a first design criterion of this invention, a
non-square supercell in a first frame of reference has a diagonal that is
equal in length to the diagonal of a square supercell in a second frame
of reference rotated at a desired screen angle to the first frame of
reference. The screen angle is a function of the lengths of the sides of
the non-square supercell in the first frame of reference. According to a
second design criterion, if the area of the corresponding square
supercell in the second frame of reference is an integer, a square
zero-shift supercell can be designed based on the lengths of the sides of
the non-square supercell in the first frame of reference.