Robust, nonempirical ab initio methods is only feasible Thus, treating even larger polypyrroles by means of On structure 28M required no less than two node months

As an illustration, a canonical CCSD(T)/cc-pVDZ calculation Hence, even for heptaphyrins with the cc-pVDZīasis set, canonical CCSD(T) hit the ceiling of our computational O( n 3 N 4), n being the number of electrons in the system and N corresponding to the number of basis functions employed Their heavy computational burden, having formal CPU-time scaling of Unfortunately, canonical CCSD(T) calculations are notorious for (b) Two 28H ⇌ 28M interconversion pathways investigated for the Hückel–Möbius Aromatic and antiaromatic macrocycles are colored in redĪnd green, respectively. The structures included in this benchmark are illustrated To benchmark results obtained at the canonical CCSD(T)/CBS level of Penta-, hexa-, and heptaphyrins-by comparing them Thus, in ref ( 6), we opted to assess the performance of differentĮxchange-correlation functionals for describing the thermochemistryĪnd kinetics of topology interconversions in N-fused It is no surprise that the selection of an exchange-correlation functionalĪppropriate for describing the energy profiles of such topological Stacking, steric effects, ring strain, aromaticity, and so forth), Interplay of different factors (hydrogen bonding, π 14− 18 Indeed, since the stability of these isomers depends on the complex 14, 15 Furthermore, different DFT studies on expanded porphyrins have arrivedĪt contradictory findings concerning the best-performing functionals

Highly dependent on the density functional employed in the calculations. Of expanded porphyrins were investigated using wave function ab initio methods and DFT methods, 6 motivated by the fact that DFT-based energetics were shown to be 10 Additional applications for expanded porphyrins, includingĬonductance switching devices 11, 12 and efficient nonlinearĪlonso et al., relative energies and isomerization pathways of a set 8, 9 Thus, these Hückel–MöbiusĪromaticity switches have already been recognized for their potentialĪpplications in molecular optoelectronic devices. Switch within a single molecule, which can easily be induced by, inter alia, an appropriate solvent, pH, temperature, and Porphyrins and Their Expected Aromaticities as a Function of the Number Representation of Different π-Conjugation Topologies of Expanded We propose the present POLYPYR21 data set as aīenchmark for localized orbital methods or, more broadly, for theĪbility of lower-level methods to handle energetics with strongly LNO-CCSD(T) method with “tight” settings is the suitable Systems plagued by strong static correlation), then Nagy and Kallay’s Mol –1 accuracy with respect to canonical relativeĮnergies is required even for Möbius-type systems (or other Weįind that Möbius(-like) structures have much stronger staticĬorrelation character than the remaining structures, and that thisĬauses significant errors in DLPNO-CCSD(T) and even DLPNO-CCSD(T 1) approaches, unless TightPNO cutoffs are employed. Porphyrins-macrocycles that can switch between Hückel,įigure-eight, and Möbius topologies under external stimuli.īoth minima and isomerization transition states are considered. In the present work, we apply both canonical CCSD(T) approximationsĪnd a variety of localized approximations to a set of flexible expanded One might expect such methods to perform less well for highly delocalized

Orbital coupled cluster theory has recently emerged asĪ nonempirical alternative to DFT for large systems.

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