Hückel-Möbius Interconversions: A Difficult Test for Electronic Structure Methods

Alonso Giner, M. (Invited speaker)

Activity: Talk or presentationTalk or presentation at a conference


Expanded porphyrins provide a versatile route to molecular switching devices due to their abil-ity to shift between several π-conjugation topologies encoding distinct properties and aromatici-ty. This unique feature has been recently exploited in three challenging nanoelectronic applica-tions, including conductance switching,[1] bithermoelectric devices,[2] and nonlinear optical switches.[3] Our findings reveal novel structure-property relationships in the field of molecular electronics and provide new selection rules to predict the occurrence of quantum interference effects in charge transport through single-molecule devices.[4]

Despite these intriguing properties, such Hückel-Möbius interconversions in expanded porphy-rins represent a complicated test for most of wavefunction methods and DFT functionals. Many of the errors can be connected to the variable degree of static correlation as a function of the topology as well as the delocalization error. Accordingly, in the second part of my talk, I will focus on the performance of a variety of quantum chemistry approaches for describing the ener-getic profiles of topology interconversions across a wide range of macrocycles.[5] Since local-ized coupled cluster theory has recently emerged as a nonempirical alternative to DFT for large systems, we have also assessed the performance of DLPNO-type and LNO-CCSD(T) ap-proaches to describe these highly-delocalized -systems. The discrepancies between canonical CCSD(T) and DLPNO-CCSD(T1) or PNO-LCCSD(T) can reach several kcal mol-1 and the deviations are proportional to several diagnostics for static correlation. The LNO-CCSD(T) approach of Nagy and Kallay offers an alternative that is more resilient to static correlation, es-pecially with tight cutoffs, and can consistently approach the canonical values to better than 1 kcal mol-1.[6]
Period26 Jul 2021
Event title12th triennial congress of the World Association of Theoretical and Computational Chemists (WATOC 2020) : Postponed to 2021 due to the COVID19 pandemic
Event typeConference
LocationVancouver, Canada
Degree of RecognitionInternational