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dc.contributor.authorFolkestad, Sarai Dery
dc.contributor.authorKjønstad, Eirik Fadum
dc.contributor.authorGoletto, Linda
dc.contributor.authorKoch, Henrik
dc.identifier.citationJournal of Chemical Theory and Computation. 2021, 17 714-726.en_US
dc.description.abstractWe present efficient implementations of the multilevel CC2 (MLCC2) and multilevel CCSD (MLCCSD) models. As the system size increases, MLCC2 and MLCCSD exhibit the scaling of the lower-level coupled cluster model. To treat large systems, we combine MLCC2 and MLCCSD with a reduced-space approach in which the multilevel coupled cluster calculation is performed in a significantly truncated molecular orbital basis. The truncation scheme is based on the selection of an active region of the molecular system and the subsequent construction of localized Hartree–Fock orbitals. These orbitals are used in the multilevel coupled cluster calculation. The electron repulsion integrals are Cholesky decomposed using a screening protocol that guarantees accuracy in the truncated molecular orbital basis and reduces computational cost. The Cholesky factors are constructed directly in the truncated basis, ensuring low storage requirements. Systems for which Hartree–Fock is too expensive can be treated by using a multilevel Hartree–Fock reference. With the reduced-space approach, we can handle systems with more than a thousand atoms. This is demonstrated for paranitroaniline in aqueous solution.en_US
dc.publisherAmerican Chemical Societyen_US
dc.rightsNavngivelse 4.0 Internasjonal*
dc.titleMultilevel CC2 and CCSD in Reduced Orbital Spaces: Electronic Excitations in Large Molecular Systemsen_US
dc.title.alternativeMultilevel CC2 and CCSD in Reduced Orbital Spaces: Electronic Excitations in Large Molecular Systemsen_US
dc.typePeer revieweden_US
dc.typeJournal articleen_US
dc.source.journalJournal of Chemical Theory and Computationen_US
dc.relation.projectNorges forskningsråd: 275506en_US
dc.relation.projectNorges forskningsråd: 263110en_US
dc.relation.projectSigma2: NN2962Ken_US

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Navngivelse 4.0 Internasjonal
Except where otherwise noted, this item's license is described as Navngivelse 4.0 Internasjonal