Lattice dynamics and specific heat of α-helical poly(L-alanine)

Abstract

We have calculated the phonon dispersion relation in α-poly(L-alanine) with all atoms in the chemical repeat explicitly included and using a recently refined force field for the polypeptide chain. The phonon density of states shows very good agreement with the inelastic neutron scattering data for this polypeptide. The specific heat for T<150 K yields better agreement with experiment than did earlier calculations. At higher temperatures the discrepancy with experiment remains. We present a simple model calculation which suggests that the source of this discrepancy may lie in the anharmonicity of the methyl torsion mode.