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Size-consistent Brueckner theory limited to double substitutions

โœ Scribed by Nicholas C. Handy; John A. Pople; Martin Head-Gordon; Krishnan Raghavachari; Gary W. Trucks

Publisher
Elsevier Science
Year
1989
Tongue
English
Weight
666 KB
Volume
164
Category
Article
ISSN
0009-2614

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โœฆ Synopsis

A size-consistent set of equations for electron correlation which are limited to double substitutions, based on Brueekner orbitals, is discussed. Called BD theory, it is shown that at fifth order of perturbation theory, BD incorporates more terms than CCSD and QCISD. The simplicity of the equations leads to an elegant gradient theory. Preliminary applications are reported.

๐Ÿ“œ SIMILAR VOLUMES

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The Brueckner model, which is a version of coupled-cluster theory where orbitals are optimized to yield zero single-excitation amplitudes (T,=O), naturally leads to the definition of an effective one-particle Hamiltonian F (or Brueckner Hamiltonian) which effectively accounts for correlation effects

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Benefittin# from the flexibility of intermediate effective Hamiltonians, we define four different dressings of the singles and doubles CI matrix which take into account the dominant effect of triple and quadruple excitations. Self-consistent versions of the dressing insure the strict separability of