Uncovering reaction sequences on surfaces through graphical methods

ZStruct is a graph-based model that generates an ensemble of plausible reaction pathways starting from a given initial state, without requiring prior knowledge of reaction intermediates. In this article, a surface-reaction oriented implementation (S-ZStruct) is introduced for unimolecular and bimolecular reactions, including sampling of different binding sites and adsorption orientations. To test the unimolecular reaction generation ability and angle sampling feature of S-ZStruct, the propanoic acid to ethylene dissociation network is studied. Starting from multiple initial orientations of two key intermediates, multiple unique reaction pathways, each with different activation energies, were discovered. Atomic layer deposition of TiN on Si(100)—involving a challenging reaction mechanism—is also studied as an example of bimolecular reactions. In addition to locating a number of expected pathways, S-ZStruct found that the little-understood step of reduction of Ti(IV) to Ti(III) likely occurs through β-hydride transfer between diamido ligands on neighboring Ti centers. These results suggest that S-ZStruct is a powerful tool for exploring surface chemistry, which will permit discoveries of reaction mechanisms in a wide variety of environments.