Magnetic Order in RuO₂: Consequences for Oxygen Evolution Catalysis from Quantum Monte Carlo

Ruthenium dioxide (RuO₂) is a state-of-the-art oxygen evolution reaction (OER) anode. Yet, its electronic ground state remains unsettled: density functional theory (DFT+U, hybrids) often predicts antiferromagnetic order in bulk RuO₂, while most OER models assume a nonmagnetic metal. We use Quantum Monte Carlo (QMC) together with controlled DFT to resolve the energetic competition between AFM and nonmagnetic RuO₂ in the bulk and on multiple RuO₂ surfaces. For each magnetic state, we evaluate adsorption energies of standard OER intermediates (*OH, *O, *OOH) and alternative peroxide-like motifs (OO–H). Magnetic order shifts the relative stability of these surface states by tenths of an eV, which directly alters the calculated OER overpotential on RuO₂. Because oxygen vacancies and surface terminations tune local Ru coordination and spin state, magnetism is not a fixed bulk property but an adjustable lever on catalytic performance of RuO_2.