Often a quantitative comparison of two structure descriptions of the same phase, coming from different sources, is difficult because the descriptions, although postulating the same space group symmetry, are described using different sets of atoms in the asymmetric unit, or different equivalent choices of origin or cell orientations. The program COMPSTRU compares two structure descriptions of the same or different composition using the following algorithm:

First, the program transforms the description of Structure 2 to the most similar configuration of the descripion of Structure 1. After that the description of Structure 2 in the most similar configuration to the description of Structure 1 is chosen so that the maximal difference d_max of the atomic positions of the matching atoms has a minimal value. The difference between the two descriptions is quantified by evaluation of the global distortion decomposed into a spontaneous strain (lattice deformation) and atomic displacement field representing the differences in the positions of the matching atoms of the two structure descriptions. In addition, for the chosen solution the program calculates two additional descriptors of the similarity.

The program COMPSTRU can also be used for the recognition of similar atomic arrangement of different compounds that is essential for the classification of crystal structures into structure types.

NOTE: The program only accepts, as input data, structural data described in a standard/default setting of the space group. If the original structural data is described with respect to an ITA setting, the program SETSTRU can be used to transform it to the standard setting. In the case of more arbitrary non-conventional settings, the tool TRANSTRU can be of some help, if the transformation to the standard setting is known.