強誘電性ポリフッ化ビニリデンⅠ型結晶の電子状態

摘要

ポリフッ化ビニリデン（PVDF）は種々の結晶構造（結rn晶多形）をとることが知られている．その構成単位（一rn次構造）は-CH_2CF_2-と単純だが，結晶中の分子鎖のコrnンホメーション（二次構造）は，トランス（T）とゴーンュrn（G,G）の結合様式の組合せで，AllT,T_3GT_3G,TGTGrnの二種類が知られている．これらの分子鎖のパッキングrn様式により理論上10種類の結晶型（三次構造）が考えらrnれており，これらの結晶多形のうち6種類の存在がXrn繰回折により実証されている．%In order to gain an insight into the characteristics of solid poly (vinylidene fluoride) (PVDF), we have carried out the quantum chemical calculation for the relationship between the form I crystal structure of ferroelectric PVDF with an all-trans conformation and the electronic structure using various ab initio DFT methods in the solid state computational tool CRYSTAL. On the basis of the calculated results, the lattice constants of the form I crystal structure and chemical bond parameters for PVDF were evaluated. As a result, the calculations with the PBEO hybrid functional agreed with the experimental X-ray diffraction analyses for the form I crystal structure of PVDF within the margin of error of ±1.4%. Further, the chemical bond parameters such as C-F bond length and F-C-F bond angle etc. were determined. Consequently, the PBEO hybrid functional was found to be useful for the computational prediction for the solid state of PVDF.