First principles determination of structural, electronic and lattice dynamical properties of a model dipeptide molecular crystal

Paul Robert Tulip (1) , Simon Bates (1)

1 SUPA School of Physics and Astronomy [Edinburgh]

We present the results of ab initio calculations of the structural, electronic and lattice dy- namical properties of the solid-state crystal of the glycyl-l-alanine dipeptide. Intramolecular bond lengths are found to be in good agreement with experimental values; lattice constants are in reasonable agreement, although it is found that discprepancies do exist. A hierarchy of hy- drogen bond strengths is found, with those between (oppositely-charged) amine and carboxy functional groups being strongest. The crystal is found to be an indirect-bandgap material, with indirect bandgaps ≈ 4.95 eV, compared to a direct bandgap of 5.00 eV. Analysis of the electronic structure reveals that the electronic states in the near vicinity of the energy gap arise from carboxylate and amide oxygen atoms. The arrangement of both molecules and hy- drogen bonds in the unit cell is found to manifest itself in increased bandwidth along specific reciprocal space directions, reflecting coupling brought about by hydrogen bonds. Determi- nation of the zone-centre lattice dynamical behaviour permits the IR absorption spectrum to be explained. Intermolecular hydrogen bonds are found to couple intramolecular motions in adjacent moelcules, revealing the importance of an accurate treatment of intermolecular interactions, even for high-frequency vibronic modes.

Mots clés: Physical Sciences

Paul Robert Tulip, Simon Bates. First principles determination of structural, electronic and lattice dynamical properties of a model dipeptide molecular crystal. Molecular Physics, 2009, 107 (20), pp.2201-2212. ⟨10.1080/00268970903224955⟩. ⟨hal-00521569⟩