title: Molecular conformations and relative stabilities can be as demanding of the electronic structure method as intermolecular calculations.
abstract: We have performed a variety of high-level electronic structure calculations on two moderately sized organic molecules and found considerable sensitivity of the intramolecular potential energy surface to the method employed. The gas-phase structure of tyrosine-glycine varies qualitatively between B3LYP and MP2 optimizations, producing different close contacts between the tyrosine ring and the glycine moiety. The relative energies of the 2-(acetylamino)benzamide conformations found in its two polymorphs can vary by over 20 kJ mol-1 between MP2 and B3LYP calculations, using the same basis set. It is shown by a novel analysis that the intramolecular equivalent of basis set superposition error competes with the errors in the intramolecular dispersion in causing this sensitivity.
authors.affiliation: Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK. t.vanmourik@ucl.ac.uk
authors.forename: Tanja
authors.initials: T
authors.lastname: van Mourik
authors.forename: Panagiotis G
authors.initials: PG
authors.lastname: Karamertzanis
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Price
mesh_terms: D001549:Benzamides / Q000737:chemistry*; D004583:Electrons; D005740:Gases / Q000737:chemistry; D005998:Glycine / Q000737:chemistry; D008956:Models, Chemical; D008968:Molecular Conformation; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D014443:Tyrosine / Q000737:chemistry
chemical_list: D001549:Benzamides; D005740:Gases; D014443:Tyrosine; D005998:Glycine