Classification of phenomenological phase transition models by the methods of equivariant catastrophe theory: models with $L=C_{nv}$ $(n=3, 4, 6)$

A classification of phenomenological phase-transition models for the two-component order parameter by the methods of equivariant catastrophe theory is proposed. The models are constructed on the basis of the number of thermodynamic parameters that are varied in an experiment (temperature, pressure, chemical potentials of admixtures, etc.) instead of the simple expansion of the thermodynamic potential in an order parameter power series. The classification of models with the order parameter symmetry groups $L=C_{nv}$ $(n=3, 4, 6)$ with the number of varied parameters from 1 to 5 is performed.