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.
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Thorsteinsson, T., Cooper, D.L., Gerratt, J., Raimondi, M. (1997). A New Approach to Valence Bond Calculations: CASVB. In: McWeeny, R., Maruani, J., Smeyers, Y.G., Wilson, S. (eds) Quantum Systems in Chemistry and Physics. Trends in Methods and Applications. Topics in Molecular Organization and Engineering, vol 16. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-4894-8_5
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DOI: https://doi.org/10.1007/978-94-011-4894-8_5
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