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Efficient model chemistries for peptides. II. Basis set convergence in the B3LYP method

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Author(s): Pablo Echenique | Gregory A. Chass

Journal: Philosophic Nature
ISSN 0974-4215

Volume: 1;
Issue: 1;
Start page: 1;
Date: 2009;
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Keywords: peptides | quantum chemistry | PES | B3LYP | basis set convergence

ABSTRACT
Small peptides are model molecules for the amino acid residues that are the constituents of proteins. In any bottom-upapproach to understand the properties of these macromolecules essential in the functioning of every living being, tocorrectly describe the conformational behaviour of small peptides constitutes an unavoidable first step. In this work,we present an study of several potential energy surfaces (PESs) of the model dipeptide HCO-L-Ala-NH2. The PESsare calculated using the B3LYP density-functional theory (DFT) method, with Dunning’s basis sets cc-pVDZ, augcc-pVDZ, cc-pVTZ, aug-cc-pVTZ, and cc-pVQZ. These calculations, whose cost amounts to approximately 10 yearsof computer time, allow us to study the basis set convergence of the B3LYP method for this model peptide. Also, wecompare the B3LYP PESs to a previous computation at the MP2/6-311++G(2df,2pd) level, in order to assess theiraccuracy with respect to a higher level reference. All data sets have been analyzed according to a general frameworkwhich can be extended to other complex problems and which captures the nearness concept in the space of modelchemistries (MCs).
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