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Coupled-cluster methods are notoriously hard to interpret using quantum-mechanical concepts such as probability amplitudes. One such set of amplitudes is particularly important in chemistry: configuration weights.
In this paper, published in the Trygve Helgaker Festschrift – a Virtual Special Issue of the Journal of Physical Chemistry A honoring former Hylleraas director Prof. Trygve Helgaker, Kristiansen et al. use the bivariational expectation-value functional to compute electron-configuration weights for any coupled-cluster model. The approach is tested for a range of conventional models – MP2, CC2, CCSD, CCSD(T), CC3, CCSDT – and the less widely used methods NOCCD and quadratic CCSD by comparing with the formally exact FCI method.
Publication date: March 3, 2025. https://doi.org/10.1021/acs.jpca.4c07443