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Symmetry breaking in O+4: an application of the Brueckner coupled-cluster method

✍ Scribed by Leslie A. Barnes; Roland Lindh

Publisher
Elsevier Science
Year
1994
Tongue
English
Weight
746 KB
Volume
223
Category
Article
ISSN
0009-2614

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✦ Synopsis

A recent calculation of the antisymmetric stretch frequency for the rectangular structure of quartet 0: using the QCISD(T) method gave a value of 37 10 cm-'. This anomalous frequency is shown to be a consequence of symmetry-breaking effects, which occur even though the QCISD (T) solution derived from a delocalized SCF reference function lies energetically well below the two localized (symmetry-broken) solutions at the equilibrium geometry. The symmetry breaking is almost eliminated at the CCSD level of theory, but the small remaining symmetry-breaking effects are magnified at the CCSD( T) level of theory so that the antisymmetric stretch frequency is still signilicantly in error. The Brueckner coupled-cluster method, however, leads to a symmetrical solution which is free of symmetry-breaking effects, with an antisymmetric stretch frequency of 1322 cm-', in good agreement with our earlier calculations using the CASSCF/CASSI method.

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