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Abstract : |
We present in this work theoretically calculated electronic spectra of charged trans-polyacetylene chains containing solitons. These calculations are based on the random phase and rotating wave approximation. Further we use correlation corrected energy levels computed in the framework of the Pariser-Parr-Pople (PPP) Hamiltonian. The geometries of the chains as functions of time have been taken from simulations within the Su-Schrieffer-Heeger (SSH) model. The spectra obtained for many time steps within a simulation are subsequently superimposed and averaged The Su-Schrieffer-Heeger model was chosen for the simulation because it is often stated, that this one-particle model is based on renormalized parameters which essentially contain already the effects of electron-electron interactions. Further at least for charged solitons the theory gives quite correct soliton widths as compared to Pariser-Parr-Pople calculations. Thus the present study is also aimed as a first step to investigate whether the SSH model is really able to yield reliable geometries in time simulations. We found that our spectra reproduce the experimentally known peaks of the solitons and band to band excitations quite well within an uncertainty of 0.3-0.5 eV. Further, the ratio of intensities of the two peaks as obtained in our calculation agrees quite well with the corresponding experimental ones. The remaining small error in intensities should be due to our use of transition dipole moments calculated from HF orbitals. Chain length might play a role in the appearance of several minima and maxima of the absorption which are not present in the experimental spectra. These different effects are currently under further study., |
