Structure and vibrational frequency determination for α-poly(vinylidene fluoride) using density-functional theory

The structure of the non-polar a-phase of poly(vinylidene fluoride) (PVDF) i determined by density-functional methods. We find very good agreement between our relaxed structure and that of previous X-ray diffraction studies. Using the relaxed structure, we have determined the infrared and Raman frequencies for the material using density-functional perturbation theory. The resulting frequencies are in excellent agreement with experiment and are comparable in accuracy to semi-empirical values for most absorbencies. In addition, we find a better agreement to experiment than a previously reported Hartree-Fock determination of vibrational frequencies in finite isolated PVDF chains. The low-frequency portion of our spectra (50-300 cm(-1)) shows better agreement with experimental values than the same frequencies found semi-empirically. Improved accuracy in this frequency range will aid in modeling phase transitions and dielectric response in PVDF. (c) 2006 Elsevier Ltd. All rights reserved.