Correlations Between Vibrational Red Shifts, Electronic Structure, and Water Dissociation on Alloy Clusters: An...

Understanding the activation mechanism of water molecules is of fundamental importance for catalytic water dissociation via water splitting. In this study, we employed first-principles molecular dynamics simulations to investigate the catalytic dissociation of H₂O on 88 alloy clusters. Our results reveal that a larger red shift in the center of the coupled ν₁ and ν₃ stretching modes of adsorbed H₂O correlates with a lower dissociation temperature. We observe an empirical correlation suggesting that dissociation is facilitated when the adsorption energy is comparable in magnitude to the HOMO-LUMO gap, which we propose as a hypothesis warranting further investigation with excited-state methods. Furthermore, comparison of the frontier molecular orbitals between precursor and intermediate states demonstrates that the number of frontier orbitals exhibiting increased overlap with the dissociating H atom is inversely correlated with the dissociation temperature. These findings provide atomic-scale insights into the activation mechanism of water dissociation on isolated gas-phase clusters and establish spectroscopic descriptors for evaluating the intrinsic reactivity of such model systems. We caution that extension of these findings to practical catalytic water splitting would require consideration of additional factors such as catalyst supports, solvents, and realistic reaction conditions.