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The reactivity of H2 on several gold clusters is studied using density functional theory with generalized gradient approximation methods, as model systems designed to study the main effects determining their catalytic properties under controlled conditions. Border effects are studied in finite linear gold chains of increasing size and compared with the corresponding periodic systems. In these linear chains, the reaction can proceed with no barrier along the minimum energy path, presenting a deep chemisorption well of E1.4 eV. The mechanism presents an important dependence on the initial attacking site of the chain. Linear Au4 chains joined to model-nanocontacts, formed by 2 or 3 gold atoms, in a planar triangle or in a pyramid, respectively, are also studied. The reaction barriers found in these two cases are E0.24 and 0.16 eV, respectively, corresponding to H2 attacking the more coordinated edge atom of the linear chain. The study is extended to planar clusters with coordinations IV and VI, for which higher H2 dissociation barriers are found. However, when the planar gold clusters are folded, and the Au–Au distances elongated, the reactivity increases considerably. This is not due to a change of coordination, but to a larger flexibility of the gold orbitals to form bonds with hydrogen atoms, when the planar sd-hybridization is broken. Finally, it is concluded that the major factor determining the reactivity of gold clusters is not strictly the coordination of gold atoms but their binding structure and some border effects.

The adiabatic global potential energy surface of the H3 + system for the lowest triplet excited state of A ' symmetry was computed for an extensive grid of conformations around the minimum region at full configuration interaction ab initia level, using a much more extended basis set than in a previous paper from the same authors. An accurate global fit (rms error lower than 27 cm-1 for energies lower than dissociation into separated atoms and lower than 5 cm-1 for energies lower than the dissociation channel) to these ab initio points and also to part of the previous.calculated points (for a total of 7689 energies in the data set) of the lowest triplet excited state of A′ symmetry is obtained using a diatomics-in-molecules approach corrected by one symmetrized three-body term with a total of 109 linear parameters and 1 nonlinear parameter. This produces an accurate global potential which represents all aspects of the bound triplet excited state of H3 + including the minima and dissociation limits, satisfying the correct symmetry properties of the system. The vibrational eigenstates have been calculated using hyperspherical coordinates with symmetry adapted basis functions with the proper regular behavior at the Eckart singularities. .The accuracy of: the vibrational levels thus obtained is expected to be better than 2 cm-1 with respect to unknown experimental values. Due to the presence of three equivalent minima at collinear geometries (D∝h) the lower vibrational levels are close to triple degenerate. Since the .interconversion barrier between the three minima is about 2640 cm-1, these states split for the upper excited vibrational levels. Such splitting can provide a key feature to identifying the unassigned transitions amongst the many H3 + lines that have been observed in hydrogen plasmas. © 2007 American Institute of Physics.

Adiabatic global potential energy surfaces, for singlet and triplet states of A′ and A″ symmetries, were computed for an extensive grid for a total of 8469 conformations of H+ 3 system at full configuration interaction ab initio level and using an extended basis set that has also been optimized for excited states. An accurate (root-mean-square error lower than 20 cm-1) global fit to the ground-state potential is obtained using a diatomics-in-molecules approach corrected by several symmetrized three-body terms with a total of 96 linear parameters and 3 nonlinear parameters. This produces an accurate global potential which represents all aspects of ground-state H+ 3 including the absolute minimum, the avoided crossing and dissociation limits, satisfying the correct symmetry properties of the system. The rovibrational eigenstates have been calculated up to total angular momentum J=20 using hyperspherical coordinates with symmetry adapted basis functions. The infrared spectra thus reproduced is within 1 cm-1 with respect to the experimental values for several transitions. © 2000 American Institute of Physics.

The invention relates to a solar cell containing a semiconductor (1) with an intermediate band (2) that is half filled with electrons, which is located between two layers of ordinary n type (3) and p type (4) semiconductors. When lighted, electron-hole pairs are formed either by a photon that absorbs the necessary energy (5) or by two photons (6, 7) that absorb less energy which pump an electron from the valence band to the intermediate band (8) and from the latter to the conductance band (9). An electrical current is generated that exits on the p side and returns via the n side. The n and p layers also prevent the intermediate band from contacting the outer metal connections, which would have resulted in a short-circuit. Said cell converts solar energy into electricity in a more efficient manner than conventional cells and contributes to the improvement of photovoltaic devices.