Molecular Engineering

, Volume 7, Issue 1–2, pp 67–85

A New Approach to Valence Bond Calculations: CASVB

  • Thorstein Thorsteinsson
  • David L. Cooper
  • Joseph Gerratt
  • Mario Raimondi
Article

Abstract

We present a new approach to the fully-variational optimization of general types of valence-bond wavefunction. Analogous techniques may be used to generate modern valence-bond representations of CASSCF structure spaces. These various procedures, which we term CASVB, are made possible by a highly efficient algorithm for performing exactly the transformations of full CI spaces that arise from general, non-unitary orbital transformations. As examples, we consider modern valence-bond representations of 'N in N' CASSCF descriptions of methane and diborane, in which the total wavefunction is dominated by covalent structures built from a common product of N nonorthogonal orbitals. These two cases highlight some of the possible differences that may arise between representations of CASSCF wavefunctions and the corresponding fully-variational valence bond results.

Valence-bond wavefunctions non-unitary orbital transformations CASVB 

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Copyright information

© Kluwer Academic Publishers 1997

Authors and Affiliations

  • Thorstein Thorsteinsson
    • 1
  • David L. Cooper
    • 1
  • Joseph Gerratt
    • 3
  • Mario Raimondi
    • 4
  1. 1.Department of ChemistryUniversity of LiverpoolLiverpoolU.K
  2. 2.Department of ChemistryChemistry Laboratory IVCopenhagen øDenmark
  3. 3.School of ChemistryUniversity of BristolBristolU.K
  4. 4.Dipartimento di Chimica Fisica ed ElettrochimicaUniversità di MilanoMilanoItaly

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