The inelastic incoherent neutron spectrum of crystalline oxamide: Experiment and simulation of a solid

The inelastic neutron scattering spectrum of crystalline oxamide, CO(NH₂)-CO(NH₂), is reported and compared with the results of Hartree-Fock and density functional theory calculations on a pentamer cluster model and the results of Car-Parrinello molecular dynamics calculations for the periodic crystal. All four hydrogen atoms of this centro-symmetric, planar sheet molecular crystal are involved in C = O-H-N hydrogen bonds. It is shown that all three of these simulations provide reasonable descriptions of the inelastic neutron scattering spectra and thus of the hydrogen bond dynamics. There is no evidence for unusual structural or dynamic effects beyond those typically associated with H-bond formation. It is argued that a polymolecular approach is needed in order to provide an adequate treatment of such strongly hydrogen bonded systems. (C) 2000 Published by Elsevier Science B.V.