Vibrational properties of PPP and PPV

We present, in this work, our preliminary results for the structural properties and the vibrational modes for the poly-para-phenylene (PPP), for the poly-para-phenylene-vinylene (PPV), and for their respective oligomers. The calculations were done by using the Density Functional Theory within the local density approximation (LDA), plane-wave description of the wave functions and the pseudopotential method, conjugated with the Unrestricted Hartree–Fock method, double-zeta basis set description of wave functions. Our results agree well (within 3% of error) with the available experimental data, whenever this comparison is possible. Based on our calculations, we show interesting aspects concerning their vibrational modes: The longitudinal acoustic modes stretches the π bonds (mainly in the vinyl group), while the transversal acoustic ones leads only to their torsion.