Linked Life Data

16848464

Source:http://linkedlifedata.com/resource/pubmed/id/16848464

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PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
29
pubmed:dateCreated
2006-7-19
pubmed:abstractText
Planar (D6h) benzene has one (1181i cm-1, b2g) and three (1844i cm-1, b2g; 462i cm-1, e2u) imaginary vibrational frequencies at the MP2/6-311++G(d,p) and MP2/6-311++G levels of theory, respectively! The spurious frequencies correspond to D3d chair (b2g) and C2v boat (e2u) out-of-plane distortions. Numerous, similar examples where planar benzene is not a minimum are documented at the MP2, MP3, and CISD levels with popular Pople-type basis sets, while the RHF, B3LYP, and BLYP methods exhibit no such problems. We show that, in the sp and spd atomic-orbital limits of MP2 theory, benzene is nonplanar. The observed failure of electron correlation methods with unbalanced basis sets to predict planar minima is not unique to benzene but is also found for other pi-delocalized molecules, including pyridine, naphthalene, anthracene, the cyclopentadienyl and indenyl anions, and the tropylium cation. Detailed mathematical analysis reveals that an insidious, geometry-dependent, two-electron basis set incompleteness error (BSIE) is responsible for the problem and that balanced, correlation-consistent constructions of basis sets are generally required to ensure reliable predictions for arenes with correlated wave functions.
pubmed:language
eng
pubmed:journal
pubmed:status
PubMed-not-MEDLINE
pubmed:month
Jul
pubmed:issn
0002-7863
pubmed:author
pubmed:issnType
Print
pubmed:day
26
pubmed:volume
128
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
9342-3
pubmed:dateRevised
2008-1-17
pubmed:year
2006
pubmed:articleTitle
Popular theoretical methods predict benzene and arenes to be nonplanar.
pubmed:affiliation
Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602, USA.
pubmed:publicationType
Journal Article