Effects of London dispersion on the isomerization reactions of large organic molecules: a density functional benchmark study.

摘要: A benchmark set of 24 isomerization reactions large organic molecules (consisting to 81 atoms) is presented (termed ISOL). The are much larger than what typically considered in thermochemical tests. To obtain reference energies, complete basis (CBS) extrapolations at the (SCS)-MP2 level have been computed that augmented by perturbative third-order corrections (SCS-MP3 and MP2.5 methods). Based on these carefully examined data, a diverse common density functionals varying from GGA double-hybrid functional with without dispersion correction (DFT-D) tested. Double-hybrid PBE0 hybrid found be methods choice for type main group thermochemistry here. For all isomerizations an average reaction energy 22.7 kcal mol−1 (in range between 0.5 74.5 mol−1), PBE0-D, B2PLYP-D B2GP-PLYP-D yield mean absolute deviations 2.5, 4.1 2.9 mol−1. Most importantly it use essential if such considered. DFT MAD lowered very significantly 1.4–5.0 when DFT-D used. Intramolecular (mainly medium-range) London interactions account some cases more 50% (41 mol−1) even though size systems remains unchanged. This study also demonstrates first time clearly typical errors expected (about 5 chemical accuracy 1 electronically well-behaved currently not reached DFT. We propose this new test as difficult challenge electronic structure claim routinely applicable molecules. suggest distance resolved diagnostic problematic