Summary
It is demonstrated how exact transformations of full CI spaces may be carried out for general, non-unitary orbital transformations, and a detailed description of an efficient implementation of this scheme is presented for Slater determinants. It is then shown how this technology may be employed in the optimization of general VB wave functions with respect to both orbital and structure coefficients. This may be done in a straightforward manner, incorporating first and second derivatives of the variational parameters.
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Thorsteinsson, T., Cooper, D.L. Exact transformations of CI spaces, VB representations of CASSCF wavefunctions and the optimization of VB wavefunctions. Theoret. Chim. Acta 94, 233–245 (1996). https://doi.org/10.1007/BF00186445
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DOI: https://doi.org/10.1007/BF00186445