Poly(ethylene oxide): Electronic Structure,Energetics,and Vibrational Spectrum

摘要

The electronic structure,energetics,and vibrational spectrum of poly(ethylene oxide)(PEO)are determined from density functional theoretical calculations on model systems(CH_2CH_2O)_nX_2,((EO)_nX_2),where X is a termination group,such as methyl or hydroxyl,and n varies from 2 to 8.Geometry optimization was performed on these linear model systems chosen to represent the noncrystalline conformer of PEO,and the convergence of selected properties(total energy,vibrational spectra)was studied.To simulate the crystalline conformer,geometry optimization and vibrational spectrum calculations were carried out on a helical(EO)_6CH_3)_2 model system.Differential scanning calorimetry data were employed to determine the crystalline fraction,used as weight for the simulation of total vibrational spectra,based on the spectra of the two conformers.The high resolution simulated spectra exhibited the contribution of individual vibrational modes to the experimentally observed broad peaks(or envelopes),while the simulated spectra with low resolution exhibited good agreement with experimental data,indicating a strong influence of the line width on the simulated spectra,caused by the distribution of chain conformations in the experimental PEO sample.The electronic structure of the linear(EO)_6(CH_3)_2 model system exhibited localization of the frontier orbitals on the oxygen atoms,where the border effect is highly pronounced,the orbitals localized on the oxygen atoms closer to the termination being highly energetic.The simulation of PEO by the finite size cluster approach utilizing oligo(ethylene oxide)model systems with six units was shown to be a good approximation to the calculation of electronic structure and vibrational spectra.