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Many chemical reactions involve bond-dissociation. This is also true forreactions at solid surfaces, in which the dissociation step is often limitingbut facilitated in comparison to gas phase reaction channels. This workconsiders hydrogen dissociation. Reliable molecular beam results are availablefor this reaction at some copper surfaces. Heterogeneous catalysis by copper issimulated. It was investigated in our previous work since it is in many ways aprototype metal presenting a close-packed surface here. These hydrogenmolecules are adsorbed at Cu(111) and fixed geometries on the dissociationreaction pathway for stretched and distant equilibrium H$_2$ are given by usingDensity Functional Theory (DFT) calculations in a plane wave basis. The PBEwave-functions at these bond-lengths serve as trial input for Quantum MonteCarlo (QMC) simulations of the ground states to obtain highly accuratecorrelated results for the associated activation barriers indicating thecatalytic effect on this dissociation. This correlation varies as bondsdissociate, requiring its accurate evaluation. Finite size effects andfixed-node error are possible limitations to accuracy of this type of QMCstudy. We are able to limit fixed node error, using certain trialwave-functions. The finite size effect is considerable, although comparing twoadsorbed geometries cancels about 90% with respect to clean surfaces. Thepseudo-potential used to represent the atomic core of copper must also bedetermined carefully: we leave 11 active electrons but include the 3d shell inthe pseudo-potential.

Quantum Monte Carlo activation barrier for hydrogen dissociation on copper to unprecedented accuracy