AIMNet2-NSE: A Transferable Reactive Neural Network Potential for Open-Shell Chemistry.

Open-shell systems such as radical intermediates are central to radical polymerization (RP), combustion, catalysis, and many other chemical and industrial processes, yet their accurate modeling presents significant computational challenges. Most of the current machine learning interatomic potentials do not distinguish between different spin states, making them unsuitable for open-shell reactive chemistry. Here we present AIMNet2-NSE (neural spin-charge equilibration), a neural network potential that incorporates spin-charge equilibration for accurate treatment of molecules and reactions with arbitrary charge and spin multiplicities. Built upon the AIMNet2 framework, AIMNet2-NSE is trained on an extensive dataset comprising 20 million closed-shell neutral and charged molecules, 13 million open-shell radical configurations, and 200K radical reaction profiles. With explicit handling of spin charges, AIMNet2-NSE enables prediction of spin-resolved properties with near-DFT accuracy while maintaining a favorable linear scaling compared to the polynomial scaling of electronic structure methods. The predictive capabilities and generalizability of our model are confirmed by evaluations on large-scale radical test sets, the industrially relevant BASChem19 benchmark, and RP reactions. Overall, AIMNet2-NSE represents a significant advancement in machine learning interatomic potentials, allowing efficient exploration of complex open-shell systems, and significantly advancing our ability to model radical reaction pathways and reactive intermediates in chemical processes where traditional quantum mechanical methods are computationally prohibitive.