Density‐functional‐based tight‐binding approach to phonon spectra of conjugated polymers

Abstract

AbstractWe apply a computationally efficient method for calculating phonon spectra to the two conjugated polymers trans‐polyacetylene and poly(para‐phenylene). The starting point of the calculation is a relaxation of the atomic coordinates based on the Density‐Functional‐Based Tight‐Binding (DFTB) approach of Porezag et al. From the relaxed geometry we calculate the force constant matrix of a suitably sized super cell and calculate the dynamical matrix by Fourier transformation.The only input required for the computation is the parametrized DFTB Hamilton and overlap matrix elements, and as a non‐self consistent TB‐method the present approach is highly efficient and therefore able to treat molecules of considerable size. The method has previously been successfully applied to vibrations in hydrocarbon molecules and single‐wall nanotubes. We demonstrate here that the approach is equally applicable to polymers, as the equilibrium configurations as well as the phonon spectra are found to be in reasonable agreement with other results from the literature. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)