Spin-Resolved Reaction-Network Exploration in AutoMeKin with Minimum-Energy-Crossing-Point Localization and an ⟨S2⟩ Single-Reference Check
Year: 2026
Type: preprint
Abstract: Automated exploration of reaction networks typically assumes a single potential-energy surface. However, 3d transition-metal catalysis often involves two-state reactivity, where the rate-determining step may occur on a different spin surface. This work presents an open-source extension of AutoMeKin that incorporates spin considerations throughout. The extension features a GFN2-xTB exploration engine with spin-handling capabilities, identification of closely lying spin states, localization of minimum-energy-crossing-points (MECP) at relevant crossings, integration of MECP nodes connected by nonadiabatic edges within the reaction graph, nonadiabatic transition-state-theory rate calculations, and a multireference diagnostic based on ⟨S2⟩ to disable the single-determinant approach where it is not applicable. The extension is tested on three different iron systems. For H2CO and Fe(CO)5, blind path sampling was utilized, whereas targeted transition-state optimization was applied to the more complex cases. Subsequently, MECPs were localized without manual intervention for Fe(CO)5 and Tp-Fe(II)-ethyl, but not for the Fe(I) alkene-isomerization catalyst.
Source: ChemRxiv
Author: Joshua M. Sims
Institution: KU Leuven
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7211934604