A perturbation stable cell comparison technique

A modified method of describing lattices (or, equivalently, unit cells) is described. In the proposed parameterization, there is no discontinuous measure of agreement such as is found in studies of reduced cells. Although the Niggli reduced cell is uniquely defined for every lattice, the angles of the reduced cell may vary wildly with minor lattice distortions. It is proposed that lattices be described by the sets of seven parameters consisting of reduced-cell edge lengths, the lengths of edges of the reduced cell of the reciprocal lattice, and the reduced-cell volume.