The internal rotation, geometry, energy, vibrational spectra, dipole moments and molecular mean polarizabilities of poly(vinylidene fluoride-tetrafluoroethylene) (P(VDF-TeFE)) of alpha- and beta-chain models Were Studied with density functional theory at B3PW91/6-31 G(d) level and compared with those of poly(vinylidene fluoride) homopolymer and P(VDF-TrFE) copolymer. The electric properties, chain conformation and stability of the copolymer influenced by the chain length and TeFE content were examined. Based on the internal rotation curves of P(VDF-TeFE) dimer models (H[CH2CF2-CF2CF2]H and H[CF2CH2-CF2CF2]H), the conformational angles, relative stabilities of alpha- and beta-conformation, and the transition energy barriers of beta --> alpha and alpha --> beta were discussed. The results show that the beta-conformation is more stable than the alpha-conformation thermodynamically and the beta --> alpha transition in P(VDF-TeFE) is more difficult than that in PVDF. Thus the copolymer Should be in favor of preventing the piezoelectric phase from depolarization. The ideal beta-chains are curved with a radius of about 30 A, which is very close to those in both PVDF and P(P(VDF-TrFE). Similar to P(VDF-TrFE), the alpha-chain P(VDF-TeFE) containing 0.50 mole fraction of TeFE is also a helical Structure. However, the g.-chain with 0.33-0.20 mole fraction of TeFE are almost linear in structure, which might be responsible for enhancing crystallinity of the copolymer. The contribution of average dipole moment per monomer unit in the beta-chain is affected by the chain Curvature and TeFE content, and there is a weakly parabolic dependence on the VDF content. The chain length and TeFE content will not significantly affect the mean polarizability per monomer unit. The calculations show that there are some characteristic vibrational modes that may be used in the identification of the alpha- and beta-phase P(VDF-TeFE) with different TeFE contents. (C) 2007 Elsevier Ltd. All rights reserved.