MODEL FOR THE LINEAR AND NONLINEAR-OPTICAL PROPERTIES OF ONE-DIMENSIONAL ORGANIC PI-CONJUGATED COMPOUNDS

It is shown that a four-site ring model allows one to interpret, on the basis of an extended Hubbard Hamiltonian, the experimental linear- and third-harmonic-generation spectra of a half-filled dimerized pi-conjugated polymer such as trans-polyacetylene. The dependence on the dimerization of the calculated electronic excitations of the model is shown to be important in explaining the experimental spectra of this type of compound.