Molecular conformations and relative stabilities can be as demanding of the electronic structure method as intermolecular calculations.
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.
van Mourik
Tanja
T
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK. t.vanmourik@ucl.ac.uk
Karamertzanis
Panagiotis G
PG
Price
Sarah L
SL
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
D001549:Benzamides; D005740:Gases; D014443:Tyrosine; D005998:Glycine