Multireference wavefunction methods for accurate adsorption energies on single-atom catalysts

Density functional theory (DFT) is the dominant electronic structure approach for elucidating reaction mechanisms and predicting reactivity of graphene-based single-atom catalysts (SACs). However, the exchange–correlation approximations made in semi-local DFT suffer from electron self-interaction error, lack of a derivative discontinuity, and a single-reference description of the electronic structure, preventing predictive accuracy for correlated SAC materials. Alternatively, high-level multireference wavefunction methods offer a more reliable description of electron correlation and can accurately treat systems with varying degrees of multiconfigurational characters involving transition metal centers, such as in SACs. In this work, we performed multireference wavefunction calculations, i.e., complete active space self-consistent field (CASSCF) coupled with complete active space second-order perturbation theory (CASPT2), to predict a key catalytic property, namely CO adsorption energy, of SACs for a widely studied reaction, electrochemical CO 2 reduction. We focused on SACs with varying 3 d transition metal centers and benchmarked the predictions with experimental measurements. Our results demonstrate how crucial it can be to use such advanced theory that goes beyond standard DFT to properly describe adsorption energies, dispensing both qualitatively and quantitatively consistent predictions with experiments. In addition, we note energy discrepancies in SAC spin states predicted across DFT and multireference wavefunction theories. This work advances fundamental understanding of electronic and catalytic properties of SACs at a higher level of accuracy than ever before, which is foundational in developing catalyst design strategies.