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

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journal contribution
posted on 02.07.2019, 00:00 by Quan Manh Phung, Carlos Martín-Fernández, Jeremy N. Harvey, Milica Feldt
We employed our recently proposed multireference approach CASPT2/CC to calculate the quintet-triplet gaps ΔETQ of a series of non-heme FeIV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.