Andrej Azman

Calculated forbidden band gap in periodic protein models indicating them to be insulators.

THE idea of electron and hole transport between distant sites in biological macromolecules, especially in fibrous proteins1 prompted quantum chemists to calculate the forbidden energy band gap in simple periodic protein models2–7. Conductivity measurements of several proteins under various conditions indicated a band gap or activation energy (E in the expression for the conductivity σ = σ0 exp(– E/2kT) as function of the temperature T) of the order of 3 eV (refs 8, 9), a value in agreement with the only theoretical energy band gap available at that time (ref. 2). Therefore, the intrinsic mechanism of semiconduction along hydrogen bridges seemed to be well established in 1960. Later, however, both experimentally10–13 and theoretically the question arose whether the conduction mechanism is really intrinsic. The more, refined all-valence-electron quantum chemical calculations5–7 indicated larger gaps (values in the range 6.1–16.7 eV were reported) than obtained in experiments. Most interestingly the calculation of Morokuma5 at complete-neglect-of-differential-overlap level showed that in a polyglycine chain the bandgap was not too sensitive to the changes of the chains conformation: in conformers with appreciable H-bonding the gap found was slightly larger than in the β-sheet conformation. This latter finding pointed out the very small influence of H-bonds on the forbidden gap of periodic protein models. These semi-empirical calculation methods were designed for molecular purposes and there is still little known of their applicability to the calculation of the gap in crystals and polymers14,19. Thus we describe here use of the more reliable non-empirical (‘ab initio’) crystal orbital method15 to calculate the band gap in a most simple polypeptide model β-polyglycine.

Numerical calculation of localized (Wannier) functions from ab-initio Hartree-Fock wave functions

Abstract The Fourier transformation necessary to obtain localized (Wannier) functions from delocalized ab-initio crystal Hartree-Fock (Bloch) functions is carried out for the one-dimensional models of solids. Combinations of Wannier functions from different bands lead to even more localized functions in close analogy to localization in molecules.

Deuteron quadrupole coupling constants in crystals with symmetrical hydrogen bonds

Deuteron quadrupole coupling constants for the free formic and trifluoroacetic acid molecules, for their acid anions and for the maleate anion were calculated using the INDO method. The results are compared with experimental values for potassium deuterium maleate and bistrifluoroacetate.