Performance of Localized Coupled Cluster Methods in a Moderately Strong Correlation Regime: Huckel-Mobius Interconversions in Expanded Porphyrins.

ABSTRACT: Localized orbital coupled cluster theory has recently emerged as a nonempirical alternative to DFT for large systems. Intuitively, one might expect such methods to perform less well for highly delocalized systems. In the present work, we apply both canonical CCSD(T) approximations and a variety of localized approximations to a set of flexible expanded porphyrins-macrocycles that can switch between Hückel, figure-eight, and Möbius topologies under external stimuli. Both minima and isomerization transition states are considered. We find that Möbius(-like) structures have much stronger static correlation character than the remaining structures, and that this causes significant errors in DLPNO-CCSD(T) and even DLPNO-CCSD(T₁) approaches, unless TightPNO cutoffs are employed. If sub-k

SUBMITTER: Sylvetsky N 

PROVIDER: S-EPMC7304861 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature