Identifying close-packed planes in complex crystal structures

It is often necessary to identify close-packed or nearly close-packed planes in a crystal. This can be done by inspection in crystal structures where one atom occupies each lattice point - i.e. face-centred cubic and body-centred cubic crystals. However, in more complex crystal structures intuitive inspection becomes rather difficult. The present paper describes a simple method for identifying close-packed or nearly close-packed planes in crystals containing more than one atom per lattice point. The method also distinguishes between 'flat' planes, where all the atom centres lie in the plane, and 'rumpled' planes, where the atom centres do not lie in the plane. The extent of the departure from true 'flatness' can also be estimated.