DIELECTRIC INSTABILITY AND LOCAL ANHARMONIC MODEL IN THE THEORY OF HIGH-T-C SUPERCONDUCTIVITY

The possible instabilities in high T-c superconductors are analyzed in the frame of the model considering the electron Hubbard correlations as well as the local anharmonic vibrations of apex oxygen O-IV. The ca lculation of the dynamic susceptibility which is performed in the gene ralized random phase approximation detects besides the instability wit h respect to charge at q = (pi/a, pi/a) the dielectric instability at q = 0. The type of instability depends on the electron concentration a nd Hamiltonian parameter values.