Heat capacity and phonon dispersion in polyselenophene in relation to the spectra of oligoselenophenes

Normal modes and their dispersion have been obtained for polyselenophene (PSe) in the reduced zone scheme using Wilson's GF matrix method as modified by Higg's for an infinite polymeric chain. The Urey Bradley potential field is obtained by least square fitting to the observed infrared and Raman bands. The results thus obtained agree well with the experimental IR and Raman values. The characteristic features of dispersion curves such as repulsion and exchange of character, crossing, van Hove type singularities have been discussed and possible explanation has been given. Heat capacity has been calculated via density-of-states using Debye relation in the temperature range 0–450 K. Possible explanation for the inflexion region in the heat capacity variation is given. The spectra of the oligomers are checked with the finite–infinite spectral relationship and are found to be in agreement.

Graphical abstractDispersion curves, heat capacity of polyselenophene and molecular electrostatic potential surfaces of octaselenophene and octatellurophene.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Phonon dispersion is obtained for polyselenophene in first Brillouin zone. ► Features of dispersion curves repulsion and exchange of character, van Hove singularities are discussed. ► Calculated heat capacity using Debye relation shows inflexion around 100 K. ► The dispersion curves are found to observe the vibrational relationship of the spectra of the oligomers and the polymer. ► Molecular electrostatic potential surfaces of 8Se and 8Te differ significantly.