An Orbital Invariant Similarity Constrained Coupled Cluster Model
Journal article, Peer reviewed
Accepted version
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Åpne
Permanent lenke
http://hdl.handle.net/11250/2639938Utgivelsesdato
2019Metadata
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- Institutt for kjemi [1397]
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Originalversjon
Journal of Chemical Theory and Computation. 2019, 15 (10), 5386-5397. 10.1021/acs.jctc.9b00702Sammendrag
We present a similarity constrained coupled cluster method able to describe conical intersections between two excited electronic states of the same symmetry. For a given pair of states, this singles and doubles method (SCCSD) is unique and orbital invariant. The computational cost scales as the sixth power with respect to the number of orbitals, and preliminary calculations indicate that the excitation energy difference relative to CCSD is within the error range of CCSD (approximately 0.10 eV). We also analyze the size-scaling properties of the orthogonality condition. For a projected orthogonality condition we show, and demonstrate numerically, that the method is rigorously size-intensive.