Comparison of HF,HF + MP2, LDA,BLYP, and B3LYP band structures of the homopolypeptides

Ab initio HF, HF + MP2, LDA DFT, BLYP DFT, and B3LYP DFT calculations are compared in the case of 19 homopolypeptides in their β pleated sheet conformation. The results show that the B3LYP method provides good results for the fundamental gaps, as compared with the values estimated on the basis of available UV spectra and intermediate exciton calculations for PolyGly and PolyAla. The HF method gives the best agreement, using Koopman's theorem for the ionization potential, taking the calculated VB_max values in the HF case if one compares them with the experimental ionization potentials of the 19 amino acids measured by mass spectroscopy. Finally, how these methods might be improved to determine the most stable conformations of the homopolypeptides is outlined. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004