Structures and piezoelectric properties of substituted β PVDF-based polymers studied by density functional theory

The geometry, dipole moments and electron properties (Mulliken charges and density of states) of substituted β PVDF-based polymers (PVDF, PVDCN, PADFB and PVDC) were studied by density functional theory. The results show that the optimised geometries of chains are bent and distorted. Dipole moments reduce with increasing chain lengths, especially in PVDCN and PVDC. PADFB presents the largest dipole moment (5.97 Debye), which can attribute to its narrow energy gap (0.12 Ha) and large Mulliken charges. It is concluded that substitution with similar radii atoms would maintain the dipole moments of the long chain, and the dipole moments would increase when the substitution reduces the energy gap in some degree.