On possible changes in crystal symmetry at structural phase transformations

Theoretical scheme is described which, at a given structure of the symmetric phase, makes it possible to list all the possible stereo groups (Gsub(D)) of the dissymetric phase and to indicate the apparent form of the multicomponent ordep parameter. This is illustrated by examined structural variations during the phase transition of the metal-dielectric to VO2. A calculation scheme of a complete problem with star number k not equal 0 has been realized by means of a concrete example. The main concern is in listing the subgroups of the given group G in each transition channel. However, after compiling complete tables for the subgroups of each channel, the application of the said scheme to any concrete transition example becomes quite simple for all 230 stereo groups. The application of the scheme for analysing the transition to VO2 has resulted in a mutually unambiguous correspondence of the experimental data with the theoretical list of possible GsubCD) groups