A Quantum Monte Carlo study of Hydrogen Adsorption on Carbon and Transition Metal Systems

We present a quantum Monte Carlo study of many molecular structures of Ti-ethylene with up to 5 H$_{2}$ molecules. These structures have been of recent interest due to energetics favorable for reversibly storing hydrogen.\footnote{E. Durgun \textit{et al}., Phys. Rev. Lett. \textbf{97}, 226102 (2006).} Diffusion Monte Carlo is employed with the fixed node approximation and pseudopotentials that have been tested for H$_{2}$ adsorbed on benzene and calculations on TiH$_{2}$ molecules.\footnote{T. D. Beaudet, Doctoral Dissertation, University of Illinois at Urbana-Champaign (2010).} Many low energy configurations were studied by calculation of ground and excited states energy surfaces. The formation energies are comparable to other work\footnote{Y. Y. Sun \textit{et al}., Phys. Rev. B \textbf{82}, 073401 (2010).} and indicate that at least 3 hydrogen molecules can be adsorbed with energies in the range considered relevant for practical hydrogen storage.