Peptide models XV. The effect of basis set size increase and electron correlation on selected minima of the ab initio 2D-Ramachandran map of For-Gly-NH2 and For-L-Ala-NH2

G. Endrédi, A. Perczel, O. Farkas, M. A. McAllister, G. I. Csonka, J. Ladik, I. G. Csizmadia

Research output: Contribution to journalArticle

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Abstract

A total of eleven basis sets from 3-21G to 6-3111++G(d,p) have been used at the HF and MP2 levels of theory for geometry optimizations of the global, γL, (φ = - 75°, Ψ = + 75°) and the second lowest, βL, (φ = - 150°, Ψ = + 150°) minimum energy conformations of the L enantiomer of HCO-NH-CH(CH3)-CO-NH2. The results showed that due to fortuitous cancellation of correlation and basis set effects, the HF/3-21G energy-difference of these conformers agrees well with the MP2/6-311++G(d,p) energy difference, while the HF/6-311++G(d,p) energy difference converges erroneously toward zero. The other legitimate conformers were optimized at the HF/3-21G, HF/6311++G(d,p), and MP2/6-311++G(d,p) levels of theory. The results showed that one of the minima disappeared at HF/6-311++G(d,p) and one more of the minima did not occur at the MP2/6-311++G(d,p) level of theory. The correlation and basis set effects stabilized the higher energy conformers.

Original languageEnglish
Pages (from-to)15-26
Number of pages12
JournalJournal of Molecular Structure: THEOCHEM
Volume391
Issue number1-2
DOIs
Publication statusPublished - Feb 28 1997

Keywords

  • Ab initio Ramanchanran map
  • Basis set size
  • Electronic structure
  • For-Gly-NH
  • For-L-Ala-NH
  • Peptide model

ASJC Scopus subject areas

  • Biochemistry
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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