Effects Of Electron Correlation On The Properties Of Exciton And Biexciton In Polymers

A key point in the theory study of the nonlinear optical(NLO) properties of the organic materials is the calculation of polarizability.Due to the low-dimension structure of the conjugated organic molecules,many sorts of elementary excitations through doping or photoexcitation will be induced in the chain,such as soliton,polaron,exciton and biexciton. These excitations will affect the NLO polarizability of polymer molecular.Xin Sun found that the biexciton showed the negative polarization under the external electric fields.This attracted many physical and chemical researchers.The effect of electron correlation on the properties of exciton and biexciton is very important.But we still don't know how the correlation affect the polarization properties at present.In this paper,based on the tight-binding Su-Schrieffer-Heeger(SSH) model and the Extended Hubbard model,by using the Configuration interaction method,to consider the electron-lattice interaction and electron-correlation,we have investigated the polarizability of the ground state and excitation state(exciton,biexciton) of the organic conjugated polymer. After taking account into electron correlation,it has been found that(1) the electron-electron interactions enhance the dimerization of the ground state in weak electron correlation region, and then decrease in strong correlation.(2) The on-site and nearest-neighbor electron interactions suppress the polarization of ground state.(3) For the exciton state the on-site electron interactions enhance the polarization while the nearest-neighbor electron interaction suppresses the polarization;in addition,for the biexciton the on-site electron interactions will increase the negative polarization and nearest-neighbor electronic interactions suppress the negative polarizationCompared with the result of Hartree-Fock method,our results demonstrated that the electron-correlation can not be neglect at stronger electron interaction system and is very important for the polarization of the excited state.