聚偏二氟乙烯晶体的电子结构和光学性质

利用含Tkatchenko-Scheffler(TS)色散修正的密度泛函理论的第一性原理方法对九种聚偏二氟乙烯(PVDF)晶相的电子结构和光学性质进行了计算. 结果表明，PVDF晶体作为一种绝缘体，能带具有密集且平直等特征，其带隙值在6.05-7.34 eV之间，且和实验值接近. 价带主要是F原子的2s和2p态起主要贡献，导带主要由C原子的2p态和H原子的1s态共同参与构成. 在0-35 eV光子能量范围内，介电函数、吸收率、反射率和折射率等光学性质发生变化主要在深紫外区域. 根据介电函数等光学参数的谱特点，可以将九种PVDF的晶相划分为{Ⅰ_p}，{Ⅱ_pu}，{Ⅱ_au，Ⅱ_ad，Ⅱ_pd，Ⅲ_pu}，{Ⅲ_au，Ⅲ_ad，Ⅲ_pd}等四类，每一类都具有相似的光学参数特点.

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

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 from6.05-7.34 eVat zero pressure and zero temperature. The calculated results of the band gap energy of the Ⅰ_p (β) and Ⅱ_ad 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: {Ⅰ_p}, {Ⅱ_pu}, {Ⅱ_au, Ⅱ_ad, Ⅱ_pd, Ⅲ_pu}, {Ⅲ_au, Ⅲ_ad, Ⅲ_pd}. The crystalline forms in each category have similar spectra features.