First-principles studies of the structural and electronic properties of poly-para-phenylene vinylene

We present first-principles investigations of the structural and electronic properties of PPV in both the isolated chain and the crystalline state. The calculations are mainly based on the local density approximation within density functional theory. With this approach, we have determined the optimal structure and torsional conformation for an isolated one-dimensional polymer chain. The predicted structural and electronic properties of PPV are generally in good agreement with recent work. However, for the vinyl C=C double bond, there exists a relatively large difference (>0.03 Å) in bond length between experiment and theory, and we postulate that this arises from a bond alternation. In the crystalline state, we find that intrachain interactions are dominant, and that interchain effects play a secondary but significant role for some bands. Effective masses are calculated from the band structure, which are helpful for understanding the opto-electronic properties of the polymer, and in particular, allow us to calculate the exciton binding energy and radius.