Electronic Structures and Optical Properties of Poly(vinylidene fluoride) Crystals

Abstract

The electronic structures and optical properties of the nine poly(vinyldene fluoride) (PVDF) crystalline forms are calculated by the first-principles method based on density functional theory with inclusion of the Tkatchenko-Scheffler (TS) dispersion corrections. The nine crystalline forms of PVDF are insulators with band gap energies from 6.05-7.34 eV at zero pressure and zero temperature. The calculated results of the band gap energy of the Ip (β) and IIad crystalline forms are close to other experimental data or calculated results. The energy bands of PVDF crystals are dense and straight. The valence bands consist mainly of F-2s and F-2p states and the conduction bands are dominated by C-2p and H-1s states. In the 0-35 eV photon energy range, the optical properties, such as dielectric function, absorption, reflectivity and refractive index, primarily change in the deep ultraviolet region in our calculations. According to the spectra features (spectral range, peaks, etc.) of the optical properties, the nine crystalline forms of PVDF can be divided into four categories: {Ip}, {IIpu}, {IIau,