Periodic HartreeÈFock methods were used to calculate the geometric and electronic properties of 2H-MoS S 2 becomes metallic and delocalized surface states form at the Fermi level due to electron transfer processes from the Li atoms to the surface layers of MoS 2 .
Solid-state NMR has been used to study the local coordination environments of the protons and alkali metal cations in hydrated alkali metal intercalation compounds of MoS 2 , A x (H 2 O) y -MoS 2 (A ) Li, Na, K, Cs). The dynamic behavior of the water molecules, which are coordinated to the intercalated A + cations, is consistent with an ordered quasi two-dimensional translational motion at room temperature. In Li x (H 2 O) y MoS 2 , the hydrated Li + cations occupy two distinct sites in the van der Waals gap that are connected by dynamic processes. Partially random motions of the H 2 O molecules are activated at room temperature.
Periodic Hartree-Fock and DFT methods were employed to calculate the geometric and electronic properties of bulk 2H-MoS 2 and of its catalytically important (101 0) edge structure. The core electrons of molybdenum and sulfur were represented by the effective core pseudo-potentials, developed by Hay and Wadt. For the calculations (101 0) type surface structures were generated by cutting sections from an 2H-MoS 2 crystal, which consists of four, six or eight rows of molybdenum and sulfur atoms. The calculated elastic constants follow the experimental constants and show that 2H-MoS 2 is an anisotropic covalent compound held together by weak dispersion interactions between neighbouring S-Mo-S units. The relaxation of the (101 0) surface of 2H-MoS 2 leads to an inner relaxation of the Mo atoms and the formation of weakly coupled surface S-S species. As a result of the surface relaxation, the electronic charge of the surface states is different to that of the bulk states: empty Mo d states move into the band gap, and the surface becomes a better electron acceptor. In all calculations the model consisting of six rows of sulfur and molybdenum atoms is the most favourable one, because it provides an accurate description of the 2H-MoS 2 surface structure and enables calculations at reasonable computation time. The calculations based on pseudo-potentials are in good agreement with all-electron calculations and confirm that, in contrast to the semiconducting bulk, the (101 0) 2H-MoS 2 surface has metallic properties.
We report a density-functional study of some properties of the adsorption process of the NO molecule on small palladium clusters (n = 1-4). The interaction between NO and the Pd n clusters is studied on various adsorption sites. Both, NO and Pd n geometrical relaxations are taken into account. The significant conformational reconstruction of the metallic cluster upon NO adsorption induces a large decrease of the NO adsorption energy. Nevertheless, the NO binding energy is strongly weakened when the molecule is adsorbed on the small Pd n clusters due essentially to an electrostatic repulsion between both N and O atoms. The possible dissociation process of NO on Pd 4 cluster is then investigated within two processes: the NO molecule does not dissociate on Pd 4 with process (i) (dissociation of the isolated gas phase NO molecule followed by the adsorption of both nitrogen and oxygen atoms on the cluster). Process (ii) which presents three successive steps (adsorption of the NO molecule, dissociation of the NO molecule adsorbed on Pd 4 , adsorption of the O atom on the cluster) is studied in details and we propose a reaction pathway locating transition states and intermediate species. The activation energy for process (ii) is high and the dissociation of the NO molecule on the Pd 4 cluster is thus highly improbable.
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