Physisorption energy of successive layers of H-2 molecules with a (100) surface of copper

International audienceMany theoretical studies already dealt with the interaction of one H-2 molecule with a metallic surface, but so far none aimed at the description of the interaction of additional layers of molecules, which is the goal of the present work. A model system consisting of a cluster of 13 Cu atoms and two/three H-2 molecules has been used to calculate with highly correlated wavefunctions the interaction of successive layers of H-2 with a surface of copper already covered by chemisorbed, dissociated H-2 molecules. A second H-2 molecule, approaching the Cu surface with different orientations, on top of a first one, is not dissociated and its physisorption interaction with the surface is calculated to be in the range 600-1000 cm(-1), approximately twice that of the first H-2 molecule. The physisorption interaction of H-2 molecules forming a third layer is estimated to be in the range of 60-100 cm(-1), which is much smaller than the interaction of the second layer with the surface but still larger than the H-2/H-2 interaction between a pair of isolated molecules. It is shown that this effect mainly results from the interactions with the ions H- and Cu+ formed on the surface. (c) 2006 Elsevier B.V. All rights reserved

Theoretical study of chemi- and physisorption processes of H2 molecules on a (100) surface of silver

International audienceA model system consisting of a cluster of 13 Ag atoms and n (n = 1,2,3) H2 molecules has been used to study, by ab initio methods, the structural and energetic characteristics of the chemi- and physisorption processes of H2 on a (100) surface of silver. The dissociative chemisorption of a first H2 molecule is analyzed in terms of hydrides formation and it is shown that several electronic states are interacting in the vicinity of the activation barrier leading to complex electronic processes. The energy of the physisorption interaction of the first H2 molecule for different orientations and that of further H2 molecules coming directly on top of the first chemisorbed one are determined with highly correlated wavefunctions. As for the (H2)(n)Cu13 system, already studied with similar approaches, it is found for the (H2)(n)Ag13 system that the physisorption energy of the second layer is enhanced by a factor close to two compared to that of the first layer due to dipolar interactions with the polarized surface. The physisorption energy of the third and further layers tends to the van der Waals H2/H2 interaction energy

Exploration of the NH3-H2 van der Waals Interaction by High Level ab initio Calculations

PosterThe intermolecular potential energy for the van der Waals complex between ammonia and the hydrogen molecule has been studied by means of the coupled cluster CCSD(T) method and aug-cc-pVXZ (X=D,T,Q,5) basis sets and with inclusion of the Boys and Bernardi counterpoise correction. For sufficiently large basis sets the only true electronic minimum energy structure of NH3-H2 is found to possess C3v point group symmetry. Various minimum energy paths for the relative motion of NH3 and H2 are analysed in order to understand the topography of the intermolecular potential. The complete basis set limit for the electronic dissociation energy is estimated to be about 253 cm−1 at the CCSD(T) level

Adsorption of successive layers of H2 molecules on a model copper surface: performances of second to fifth rung exchange-correlation functionals

9 pagesInternational audienceThe interaction of H2 molecules with a Cu(100) metallic surface has been investigated by DFT approaches using a (H2)nCu13 cluster model. Nine exchange-correlation functionals, belonging to the Generalized Gradient Approximations (GGA), meta GGA (mGGA), hybrid Kohn-Sham/Hartree- Fock models, either based on GGAs or mGGAs, range-separated hybrids, and double-hybrid families, have been tested on the chemisorption and physisorption processes involving one or two H2 layers. The addition of an empirical correction for dispersion has also been tested for some of these functionals. The calculated energies and structural parameters were compared to sophisticated Multi Reference Con guration Interaction including Davidson's correction for quadruple excitations (MRCI+Q). Our results show that among the nine considered exchange-correlation functionals, none can accurately reproduce all processes involved in the successive layers adsorption. Although an hybrid based on a mGGA such as M06-2X can quantitatively describe both the physisorption step and dissociation barriers involved in the adsorption of the rst H2, it fails to reproduce its chemisorption. On the other hand, signi cant discrepancies with the reference post-HF data are obtained for the description of the second layer interaction, no matter which functional is considered, outlining the need of improvement and/or development of exchange-correlation functionals suitable for complex systems such as H2/H2Cu

Exploration of the NH3-H2 van der Waals interaction by high level ab initio calculations

International audienceThe intermolecular potential energy for the van der Waals complex between ammonia and the hydrogen molecule has been studied by means of the coupled cluster CCSD(T) method and aug-cc-pVXZ (X = D, T, Q, 5) basis sets and with inclusion of the Boys and Bernardi counterpoise correction. For sufficiently large basis sets the only true electronic minimum energy structure of NH3-H2 is found to possess C3v point group symmetry. Various minimum energy paths for the relative motion of NH3 and H2 are analysed in order to understand the topography of the intermolecular potential. The complete basis set limit for the electronic dissociation energy is estimated to be about 253 cm−1 at the CCSD(T) level