EN
Studies on the phases of CuInP_{2}S_{6} crystal exhibiting phase transitions of the order-disorder type are performed. A possibility for the cooperative Jahn-Teller effect to occur in this crystal is analyzed. For this purpose, the procedure of constructing the potential energy matrix is generalized for the case of crystal and it is illustrated by the construction of the adiabatic potentials for Γ_{5}-Γ_{5} vibronic coupling for the proto- and paraelectric phases of CuInP_{2}S_{6}. The structure of the obtained potentials is analyzed together with the discussion on the appearance of spontaneous polarization in this crystal.