Ab initio dynamics study of poly-para-phenylene vinylene

Abstract

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We present an ab initio dynamics investigation within a density-functional perturbation theory framework of the properties of the conjugated polymer poly-para-phenylene vinylene ͑PPV͒ in both the isolated chain and crystalline states. The calculated results show that for an isolated chain, most of the vibrational modes correspond to experimentally observed modes in crystalline PPV. However, additional hitherto unidentified modes have been observed in experiment and our calculations on crystalline material have allowed us to assign these. We also present the results of calculations of the polarizability and permittivity tensors of the material, which are in reasonable agreement with the typical values for conjugated polymers. Dynamical Born effective charges ͓S. Baroni, S. de Gironcoli, A. Dal Corso, and P. Giannozzi, Rev. Mod. Phys. 73, 515 ͑2001͔͒ are calculated and compared with atomic charges obtained from Mulliken population analysis ͓M. D. Segall, C. J. Pickard, R. Shah, and M. C. Payne, Mol. Phys. 89, 571 ͑1996͔͒ and we conclude that effective charges are more appropriate for use in the study of the dynamics of the system. Notable differences are found in the infrared-absorption spectra obtained for the isolated chain and crystalline states, which can be attributed to the differences in the crystalline packing effects, which clearly play a key role in influencing the lattice dynamics of PPV.

Lattice dynamics of polyaniline and poly(p-pyridyl vinyline): First-principles determination

“…In Table II, it is found that the major contribution to the average polymer polarizability ␣ av DFPT ͓=Tr͑␣ DFPT ͒ /3͔ is the component ␣ zz . For PPyV, the three individual principal components are very similar to those of an isolated PPV chain, 23 which may be attributed to the similarity of the structures of PPyV and PPV. Both PPyV and PPV have the property that ␣ zz ӷ ␣ yy and ␣ yy Ӎ ␣ xx .…”

“…The contributions to the charge density from different atoms can be clearly seen, and it is apparent that the polarizability is de- pendent on the atomic environment. Notable differences can be found in the first-order densities for the pristine aromatic polymers such as PPV, 23 and for PANi and PPyV, especially in the vicinity of the heteroatom nitrogen. Furthermore, according to Table II, the polarizabilities are strongly anisotropic with a relatively large response for an electric field applied along the z axis.…”

“…Actually, these mode frequencies are quite stable compared with the corresponding vinyl mode 1613.7 cm −1 of PPV. 23 The fact that the vinyl oscillating modes occur in the same frequency range for these systems suggests that the nitrogen atom does not have much influence on them.…”

“…Notable differences can be found in the predicted ir spectra for PANi, PPyV, and undoped PPV. 23 It is known that PANi and PPyV are conducting polymers; this implies that the nitrogen doping atom plays a key role in the transport mechanisms of the materials.…”

“…22 Very recently, an ab initio dynamics study has been carried out for the undoped polymer PPV. 23 In this work we present a first-principles investigation of the dynamical properties of the conducting polymers PANi and PPyV. We first study the vibrational properties of the conducting materials; then we concentrate on the electric field response and Born effective and Mulliken charges.…”