Periodic density functional theory calculations for 3-dimensional polyacetylene with empirical dispersion terms

Abstract

We report periodic B3LYP density functional theory calculations for three-dimensional (3D) trans-polyacetylene (t-PA) fibers. Empirical dispersion terms, as proposed by Grimme, are included with an appropriate re-scaling to yield the B3LYP+D* method implemented in CRYSTAL06. The dispersion corrections are critical for obtaining correct unit cell parameters. In our calculations the out-of-phase P2₁/n structure turns out to be a transition state for the interchain relative translational motion, which lies about 0.35 kcal mol⁻¹ above the two symmetrically located in-phase P2₁/a minima. These results provide a possible new explanation for the observed XRD intensities. Our calculations should also be useful for comparison with more costly non-empirical treatments of 3D PA and other π-conjugated polymers.