The MOBH35 metal-organic barrier heights reconsidered: performance of local-orbital coupled cluster approaches in different static correlation regimes

TL;DR

This study reevaluates the MOBH35 benchmark for organometallic reactions using advanced coupled cluster methods, revealing the strengths and limitations of various local orbital approaches across different static correlation regimes.

Contribution

It provides a comprehensive comparison of local orbital coupled cluster methods against canonical CCSD(T) for MOBH35, highlighting their performance in static correlation regimes and revising key benchmark values.

Findings

LNO-CCSD(T) converges smoothly to canonical CCSD(T)

DLPNO-CCSD(T) and PNO-LCCSD(T) may fail under strong static correlation

Revised MOBH35 reference values differ notably for reactions involving iron

Abstract

We have revisited the MOBH35 (Metal-Organic Barrier Heights, 35 reactions) benchmark [Iron, M. A.; Janes, T. J. Phys. Chem. A 2019, 123 (17), 3761-3781; ibid. 2019, 123, 6379-6380] for realistic organometallic catalytic reactions, using both canonical CCSD(T) and localized orbital approximations to it. For low levels of static correlation, all of DLPNO-CCSD(T), PNO-LCCSD(T), and LNO-CCSD(T) perform well; for moderately strong levels of static correlation, DLPNO-CCSD(T) and (T1) may break down catastrophically, and PNO-LCCSD(T) is vulnerable as well. In contrast, LNO-CCSD(T) converges smoothly to the canonical CCSD(T) answer with increasingly tight convergence settings. The only two reactions for which our revised MOBH35 reference values differ substantially from the original ones are reaction 9 and to a lesser extent 8, both involving iron. For the purpose of evaluating DFT methods for MOBH35, it would be best to excise reaction 9 entirely as its severe level of static correlation is just too demanding a test. The magnitude of the difference between DLPNO-CCSD(T) and DLPNO-CCSD(T1) is a reasonably good predictor for errors in DLPNO-CCSD(T1) compared to canonical CCSD(T); [...]