Importance of a nonlocal description of electron-electron interactions in modeling the dissociative adsorption of H₂ on Cu(100)

Describing the dissociation of molecules on metal surfaces is of major importance in understanding processes such as corrosion or heterogeneous catalysis. Because of its high efficiency and reasonable accuracy, density functional theory (DFT) is the method of choice in this field nowadays, but it can be expected that the semilocal treatment of the exchange-correlation introduces fundamental errors. To understand those errors, it is possible to reduce the complexity of the problem to, for example, describe the dissociation of H₂ on Cu(100). In this work, we model this process for an embedded, metallic cluster comparing coupled cluster, configuration interaction, and semilocal DFT calculations. We calculate a two-dimensional potential energy surface (PES) and identify the minimum energy pathway (MEP) for dissociation, the transition state, and also the dissociation minimum. Compared to DFT calculations, the interactions between the molecule and the surface are far more long ranged in explicitly correlated methods, and the dissociation is also far more exothermic. To accurately describe dissociation, it is necessary to take the multideterminant nature of the wave function in embedded MRCI+Q calculations into account. For them, we find excellent agreement with experiment. On the basis of these calculations, we discuss the reasons for shortcomings of semilocal density functionals described in recent literature. These results clearly show that an accurate nonlocal treatment of the electron-electron interactions qualitatively changes the potential energy surface for molecules interacting with extended systems and possibly improves agreement with experiments. It will be interesting to see how they can be transferred to and affect more complex problems such as modeling entire reaction pathways.