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Correlation corrected band structures of homopolypeptides v. B3LYP band structures of 19 homopolypeptides
Author(s) -
Bogar F.,
Ladik J.
Publication year - 2004
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.20107
Subject(s) - basis set , molecular physics , band gap , spectral line , exciton , brillouin zone , conduction band , ab initio , chemistry , dispersion (optics) , physics , computational chemistry , condensed matter physics , density functional theory , optics , electron , organic chemistry , quantum mechanics , astronomy
Abstract Ab initio B3LYP crystal orbital (CO) calculations have been performed on the 19 homopolypeptides (PolyGly, PolyAla, PolySer, PolyThre, PolyLeu, PolyiLeu, PolyVal, PolyAspAc, PolyAsp, PolyGlutAc, PolyGlut, PolyHist, PolyProl, PolyCyst, PolyMeth, PolyTyr, PolyPhenAla, PolyArg, and PolyLys) in their β pleated sheet conformation. Keeping the main chain conformation fixed as in PolyGly, the side chain geometries were optimized. For the calculation 2 n +1 different k points were used with n = 8 for the case of simpler and n = 10 for more complicated side chains. The basis set applied was the double ζ one of Clementi. According to the results obtained, the conduction bands are shifted upward and the valance band downward, compared with the results of previous BLYP 1 and LDA 7 CO calculations. The bandwidths are similar to the previous cases. The band edges are in many cases not at the endpoints of the first Brillouin zones, causing nonmonotonous dispersion of both the conduction bands (CB) and the valance bands (VB), respectively. The fundamental gap values due to the upward shifts of the CB and downward shifts of the VB are substantially larger than in the case of our previous DFT CO calculations (values 6.0–7.0 eV). They are very close to the gap values, which can be estimated on the basis of experimental ultraviolet (UV) spectra of some homopolypeptides and on the basis of intermediate exciton theoretical calculations (6.5–7.5 eV). These surprisingly good results for the gaps are due to the compensation of errors (LDA or BLYP gives too small and simple HF provides too large gap values) in the B3LYP method. The admixture of the exact HF exchange with a weight of 0.19 obviously compensates the self interaction error occurring in the LDA or BLYP methods. This article discusses whether/how this result could be established by other B3LYP CO calculations on simple polymer chains and on stacked systems (e.g., nucleotide base stacks). Furthermore, a comparative analysis of the ground state DFT methods, the HF method and of the optimized effective potential method could throw more light on our successful theoretical results for the gaps of the homopolypeptides. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004