Freitag vormittags Vorträge - Bunsentagung - Technische Universität ...

Freitag 21.05.2004, 15:30 Uhr
Vortrag - Theoretische Chemie
Correlation Corrected Band Structures of
Biopolymers
Janos Ladik
Egerlandstr.3. 91058 Erlangen
C
23
Ab initio correlation corrected energy band structures have been
calculated for the four nucleotide base stacks and for 19 homopolypeptides.
In the case of the base stacks (in their DNA
B conformation) the band gaps obtained are in a rather good
agreement with experiment (estimated on the basis of intermediate
exciton theory) in th HF+MP2 case applying a double zeta
basis set+a set of p functions centered on a dummy molecule situated
in the middle of the stacking distance. In the HF case the
positions of the upper edges of the valence bands are also in quite
good egreement with the experimental ionization potentials if
one applies Koopman’s theorem. The 19 homopolypeptides were
taken in their beta pleated sheet conformation and consist of
those of the esential amino acids with the exception of Poly-
Tryp. In the HF and HF+MP2 cases the gaps obtained are too
large while the LDA and BLYP DFT-s provide too small gaps.
Finally the B3LYP gaps agree quite well with those estimated
on the basis of exciton theory (PolyGly and PolyAla) as well
obtained from the experimental exciton spectra of PolyGlut and
PolyLeu. There are no experimental ionization potentials for the
homopolypeptides available. On the other hand the HF valence
band upper edges are in reasonable agreement with the experimental
ionization potentials of the single amino acids (8-11eV)
and of those of peptide bonds in simpler compounds.