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Cluster perturbation theory. II. Excitation energies for a coupled cluster target state


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dc.contributorFilip Pawlowski, flp0008@auburn.eduen_US
dc.creatorPawlowski, Filip
dc.creatorOlsen, Jeppe
dc.creatorJorgensen, Poul
dc.date.accessioned2020-05-07T18:27:29Z
dc.date.available2020-05-07T18:27:29Z
dc.date.created2019
dc.identifier10.1063/1.5053167en_US
dc.identifier.urihttps://aip.scitation.org/doi/abs/10.1063/1.5053167en_US
dc.identifier.urihttp://hdl.handle.net/11200/49797
dc.description.abstractIn cluster perturbation (CP) theory, we consider a target excitation space relative to a Hartree-Fock state and partition the target excitation space into a parent excitation space and an auxiliary excitation space. The zeroth-order state is in CP theory a coupled cluster (CC) state in the parent excitation space, and the target state is a CC state in the target excitation space. In this paper, we derive CP series for excitation energies in orders of the CC parent-state similarity-transformed fluctuation potential where the zeroth-order term in the series is an excitation energy for the CC parent state response eigenvalue equation and where the series formally converge to an excitation energy for the CC target state response eigenvalue equation. We give explicit expressions for the lowest-order excitation energy corrections. We also report calculations for CP excitation energy series for various parent and target excitation spaces and examine how well the lower-order corrections can reproduce the total excitation energies. Considering the fast local convergence we have observed for the CP excitation energy series, it becomes computationally attractive to use low-order corrections in CP series to obtain excitation energies of CC target state quality. For the CPS(D-n) series, the first-order correction vanishes, the second-order correction becomes the CIS(D) model, and for the CPS(D-3) model, our calculations suggest that excitation energies of CCSD quality are obtained. The numerical results also suggest that a similar behavior can be seen for the low-order excitation energy corrections for CP series where the parent state contains more than a singles excitation space, e.g., for the CPSD(T) model. We therefore expect the low-order excitation energy corrections in CP series soon to become state-of-the-art models for determining excitation energies of CC target state quality. Published under license by AIP Publishing.en_US
dc.formatPDFen_US
dc.publisherAMER INST PHYSICSen_US
dc.relation.ispartofJournal of Chemical Physicsen_US
dc.relation.ispartofseries0021-9606en_US
dc.subjectEXCITED ELECTRONIC STATES; POLARIZATION PROPAGATOR; CONFIGURATION-INTERACTION; TRIPLE-EXCITATIONS; RESPONSE FUNCTIONS; DOUBLES MODEL; SINGLES; IMPLEMENTATION; SPACE; CC3en_US
dc.titleCluster perturbation theory. II. Excitation energies for a coupled cluster target stateen_US
dc.typeTexten_US
dc.type.genreJournal Article, Academic Journalen_US
dc.citation.volume150en_US
dc.citation.issue13en_US
dc.citation.spage134109en_US
dc.description.statusPublisheden_US
dc.creator.orcid0000-0002-5928-2140en_US

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