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15 páginas, 6 figuras, 5 tablas., We describe an implementation of Hedin's GW approximation for molecules and clusters, the complexity of which scales as O(N3) with the number of atoms. Our method is guided by two strategies: (i) to respect the locality of the underlying electronic interactions and (ii) to avoid the singularities of Green's functions by manipulating, instead, their spectral functions using fast Fourier transform methods. To take into account the locality of the electronic interactions, we use a local basis of atomic orbitals and, also, a local basis in the space of their products. We further compress the screened Coulomb interaction into a space of lower dimensions for speed and to reduce memory requirements. The improved scaling of our method with respect to most of the published methodologies should facilitate GW calculations for large systems. Our implementation is intended as a step forward towards the goal of predicting, prior to their synthesis, the ionization energies and electron affinities of the large molecules that serve as constituents of organic semiconductors., D.S.P. and P.K. acknowledge financial support from the Consejo Superior de Investigaciones Científicas (CSIC), the Basque Departamento de Educación, UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-02), and the ETORTEK program funded by the Basque Departamento de Industria and the Diputación Foral de Guipuzcoa.

3 páginas, 3 figuras.-- et al., Infrared spectroscopy is demonstrated to sensitively detect electronic excitations in 1-nm-wide wires made of indium. The polarization-dependent spectra measured at room temperature show a strong broadband plasmonic absorption feature in the direction parallel to the wires, while in the perpendicular direction the wires stay nearly transparent in the same spectral range. At 88 K the wires do not show this broadband absorption anymore, but instead, several interband-transition features arise for both polarizations, in agreement to the gap opening of the metal-to-insulator transition as known for this one-dimensional structure., This work is a part of the joint project “Strategic International Cooperative Program” funded by DFG-Germany (Grant No. PU193/9) and JST-Japan, and Spanish MICINN (Grant No. FIS2007-66711-C02-02) and Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT).

The authors have investigated the structure and energetics of the first hydration layer on NaCl(100) by means of density functional calculations. They have analyzed in detail the role of the hydrogen bond between the adsorbed molecules for the determination of the most favorable structures. They have shown that, using the water dimers as basic building blocks, very stable structures can be constructed. They discuss here two important examples: (i) a model with (1×1) periodicity at 2 ML coverage, and (ii) icelike bilayers with a c(4×2)unit cell at 1.5 ML. Both structures present high adsorption energies per water molecule of ∼570meV, in comparison to the 350meV adsorption energy obtained for the previously studied (1×1) structures composed of weakly interacting monomers. Based on these findings, they propose an interpretation for the experimental observations of Toennies et al. [J. Chem. Phys. 120, 11347 (2004)], who found a transition of the periodicity of the first hydration layer on NaCl(100) from (1×1) to c(4×2) upon electron irradiation. According to the model, the transition would be driven by the partial desorption of (1×1) bilayer structures corresponding to a local coverage of 2 ML and the further rearrangement of the remaining water molecules to form a quasihexagonal structure with c(4×2) periodicity at coverage close to 1.5 ML., This work has been supported by the Basque Departamento de Educación, the UPV/EHU (Grant No. 9/UPV 00206.215-13639/2001), the Spanish Ministerio de Educación y Ciencia (Grant No. FIS2004-06490-C3-00), the European Network of Excellence FP6-NoE “NANOQUANTA” (Grant No. 500198-2), and the projects “NANOMATERIALES” and “NANOTRON” funded by the Basque Departamento de Industria, Comercio y Turismo within the ETORTEK programme and the Departamento para la Innovación y la Sociedad del Conocimiento from the Diputación Foral de Guipúzcoa.

Cement-based materials are ubiquitous in almost all built environment. In spite of this, little is known about the formation and the role played by the silicate chains always present in the cement nanostructure. By means of first principles simulations we provide compelling evidence on the pivotal role played by certain ionic species in the formation of the silicate chains inside the cementitious matrix. Moreover, we corroborate the experimental evidence which shows that the length of the most stable chains with m Si atoms follows a magic-number sequence: m=3n-1 with n=1,2,... Our results have been applied in the development of new higher performance cement-based materials by adding nanosilica. © 2007 American Institute of Physics.

The excitation of a fullerene-cage vibrational mode by inelastic tunneling electrons has been observed on single C60 molecules adsorbed on Ag(110). The vibration is assigned to the Hg(ω2) mode. A critical enhancement of the inelastic signal was found on fullerenes oriented along one of their symmetry axis upon adsorption. In strong coincidence, those fullerenes maintain a resonance structure at the Fermi level that resembles the first unoccupied molecular orbital distribution of a free molecule, as determined by comparison with ab initio calculations. The degree of symmetry of the adsorbed fullerene is found to be crucial for resonant mechanism of vibrational excitation. We also propose that mode degeneracy splitting may reduce mode detection., J.I.P. thanks the EU commission for his contract under the Mary Curie scheme. J.G.H. thanks the Max-Planckfor support of his visit to the Fritz-Haber-Institut.