Optical and electronic properties of poly(para-phenylene) by first principles calculations and experimental results

Summary form only given. We have performed ab initio band structure calculations for ID and 3D crystalline poly(para-phenylene) using the LAPW and the pseudopotential method, which are based on density functional theory. The energy gap can be varied between 0 and 4 eV by changing the structural parameters. We predict a torsion angle of 18/spl deg/ for the 3D structure and 27/spl deg/ for the ID chain between two adjacent rings. The 3D structure was optimized for the space groups Pbam and Pnnm by symmetry restricted force calculations. This space groups are suggested by X-ray measurements on poly(para-phenylene) powder samples. The interchain coupling leads to a band splitting by more than 0.5 eV. For the force free geometry we present the band structure and calculations of the dielectric tensor and the absorption coefficient in comparison with optical absorption measurements.