OPTICAL AND ELECTRONIC-PROPERTIES OF CRYSTALLINE POLY(PARA-PHENYLENE)BY FIRST-PRINCIPLES CALCULATIONS AND EXPERIMENTAL RESULTS

We have performed first-principles LDA band structure calculations for 1D and 3D crystalline poly(para-phenylene) using the LAPW and the pse udopotential method, which are based on the density functional theory. The band gap can be easily tuned through the whole visible region by varying the structural parameters. Optimized structural parameters hav e been determined for the orthorhombic space group Pbam and the 1D cha in. We predict a torsion angle between two adjacent rings of 18 degree s for the 3D structure and 27 degrees for the 1D chain. The interchain coupling leads to band splittings of nearly 1 eV. The absorption coef ficient has been calculated and compared to experimental data. The exc ellent agreement indicates that excitonic effects are weak. Calculatio ns of the luminescence emission efficiency are presented.