Electronic properties of PPP-oligomers investigated from first-principles

We hale performed first-principles calculations for crystalline oligomers o f poly(para-phenylene) in the framework of density functional theory. The b and structure of the 2-, 3- and 4- unit oligomer is determined. The band ga p as a function of chain length excellently reproduces the experimental fin dings. Additionally we have studied the effects when generalized gradient c orrections (GGA) are applied instead of the local-density approximation (LD A) for exchange- and correlation effects.