Ab Initio Calculations for Spin-Gaps of Non-Heme Iron Complexes

Quan Manh Phung; Carlos Martín-Fernández; Jeremy N Harvey; Milica Feldt

doi:10.1021/acs.jctc.9b00370

Ab Initio Calculations for Spin-Gaps of Non-Heme Iron Complexes

J Chem Theory Comput. 2019 Aug 13;15(8):4297-4304. doi: 10.1021/acs.jctc.9b00370. Epub 2019 Jul 5.

Authors

Quan Manh Phung¹, Carlos Martín-Fernández¹, Jeremy N Harvey¹, Milica Feldt¹

Affiliation

¹ Department of Chemistry , KU Leuven , Celestijnenlaan 200f , Box 2404, 3001 Leuven , Belgium.

PMID: 31265281
DOI: 10.1021/acs.jctc.9b00370

Abstract

We employed our recently proposed multireference approach CASPT2/CC to calculate the quintet-triplet gaps ΔE_TQ of a series of non-heme Fe^IV═O species and subsequently used these results to benchmark density functional theory (DFT) as well as two variants of local coupled-cluster approaches (DLPNO-CCSD(T) and LUCCSD(T0)). We showed that current implementations of the local coupled-cluster method are not sufficiently accurate. DLPNO-CCSD(T) systematically overstabilizes the quintet state, whereas LUCCSD(T0) overestimates the triplet one. This sort of systematic bias may be helpful in improving local correlation methods and can also be used as the basis for a simple correction scheme.