Electronic structure and transport in disordered organic systems

The strongly-bound approximation is used to examine the effects of disorder on the electron energy spectrum. It is assumed that the exchange integrals in the nearest-neighbor approximation are random functions. The limiting cases of slight and pronounced disorder are discussed with allowance for correlation. The effects of some particular types of correlation are examined as regards type of spectrum and band broadening. It is found that the spectrum splits into two branches in the limiting case of extensive disorder. An expression for the electrical conductivity is derived for the case of slight disorder.