THE CONTINUUM THEORY OF DELOCALIZED AND SELF-TRAPPED POLARONS AND BIPOLARONS IN SOLIDS

The continuum theory of delocalized (D) and self-trapped (S) polarons and bipolarons is developed within the adiabatic approximation and the direct variational approach. The role of each taken separately and the combined effects of the short- and long-range electron-lattice interactions as well as electron correlations in the formation of D- and S-polarons and bipolarons is considered in detail. It is shown that the simultananeous accounting of these effects leads to increasing the ratio of the binding energy of a D-bipolaron to double the energy of a D-polaron to 0.372 at epsilon(infinity)/epsilon(0)-->0 and to a noticeable expansion of the existence regions (epsilon(infinity)/epsilon(0) less than or equal to 0.16) Of these bipolarons. Numerical results show that the short-range electron-lattice interaction and electron correlation also play an important role in the formation of the S-bipolarons. The possible relations of the D- and S-bipolarons to superconductivity in high-temperature and other superconductors are considered.