Effect of electric field on the structure and piezoelectric properties of poly(vinylidene fluoride) studied by density functional theory

The geometry and piezoelectric properties of chain in PVDF under different electric fields are studied by density functional theory (DFT). The simulation gives optimized geometry of PVDF of α chain and β chain, with rotation angle around ±50° and arbitrary angle between 175° and 185° respectively. The energy barrier is about 16.16 kJ/mol in the chain transition from α chain to β chain, and the one of reverse transition is about 6.24 kJ/mol. The positive electric decreases the energies of α chain and β chain. There would be a critical positive electric field inducing the transition from α chain to β chain. Positive electric field increases dipole moment of the β chain and has few effects on mean molecular polarizibility. It is found that the change of geometry increases dipole moment and the change of electronic properties decrease dipole moment under positive electric field and the geometry plays an important role.