The internal rotation, geometry, energy, vibrational spectra, dipole moments and molecular polarizabilities of poly (vinylidene fluoride) (PVDF) of a- and b-chain models were studied by density functional theory at B3PW91/6-31G (d) level. The effects of chain lengths and monomer inversion defects on the electric properties and vibrational spectra were examined. The results show that the tgtgo conformation angle between g and go is about 55 and the ttt conformation is a slightly distorted all-trans alternating planar zigzag with 175 repeating motif. The average distance between adjacent monomer units in the b-PVDF is 2.567