The universal state selective (USS) multireference approach is used to construct new energy functionals which offer a possibility of bridging single and multireference coupled cluster theories (SR/MRCC). These functionals, which can be used to develop iterative and non-iterative approaches, utilize a special form of the trial wavefunctions, which assure additive separability (or size-consistency) of the USS energies in the non-interacting subsystem limit. When the USS formalism is combined with approximate SRCC theories, the resulting formalism can be viewed as a size-consistent version of the method of moments of coupled cluster equations employing a MRCC trial wavefunction. Special cases of the USS formulations, which utilize single reference state specific CC [V. V. Ivanov, D. I. Lyakh, and L. Adamowicz, Phys. Chem. Chem. Phys. 11, 2355 (2009)]

https://doi.org/10.1039/b818590p
and tailored CC [T. Kinoshita, O. Hino, and R. J. Bartlett, J. Chem. Phys. 123, 074106 (2005)]
https://doi.org/10.1063/1.2000251
 expansions are also discussed.

Topics
Quantum chemical calculations, Coupled-cluster methods, Potential energy surfaces, Multi-reference configuration interaction, Self consistent field methods, Energy forms and sources, Leptons, Transition state, Hilbert space, Operator theory
© 2013 AIP Publishing LLC.
2013
AIP Publishing LLC
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