Density-functional study for the oligomers of poly(para-phenylene): Band structures and dielectric tensors

The electronic and optical properties of the oligomers of poly(para-phenyle ne) (PPP) in their crystalline phases are calculated. In particular, the 2- , 3-, 4-, and the technically most important 6-unit oligomer para-hexapheny lene (6P) are considered. The electronic band structures are compared with the corresponding molecular orbitals in isolated molecules and the effect o f intermolecular interactions is discussed. Connections between previous st udies on the band structure of three-dimensional PPP and the present work a re established. From the quasiparticle band structures the dielectric tenso rs are calculated and discussed also with respect to the corresponding tran sitions in the isolated molecules.