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Kibalchenko M.,University of Cambridge | Yates J.R.,University of Oxford | Massobrio C.,CNRS Institute of Genetics and of Molecular and Cellular Biology | Pasquarello A.,Ecole Polytechnique Federale de Lausanne | Pasquarello A.,Institute Romand Of Recherche Numerique En Physique Des Materiaux Irrma
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Structural assignments are determined for 77Se and 73Ge chemical shifts through density-functional NMR calculations for GeSe2, Ge4 Se9, and GeSe crystals. In particular, a very good agreement between calculated and measured 77Se isotropic chemical shifts and anisotropies is found for the GeSe2 crystal, for which experimental data are available. These assignments provide a consistent interpretation of experimental 77Se spectra of Gex Se1-x glasses, indicating that the contribution from Ge-Se-Se linkages overlaps with that from Ge-Se-Ge linkages in corner-sharing tetrahedral arrangements, thereby dismissing the occurrence of a bimodal phase. © 2010 The American Physical Society. Source


Kibalchenko M.,University of Cambridge | Yates J.R.,University of Oxford | Pasquarello A.,Ecole Polytechnique Federale de Lausanne | Pasquarello A.,Institute Romand Of Recherche Numerique En Physique Des Materiaux Irrma
Journal of Physics Condensed Matter | Year: 2010

NMR parameters of 73Ge and 17O in vitreous GeO 2 and quartz GeO2, including the isotropic shifts, the quadrupole coupling constants CQ, and the electric-field-gradient asymmetry parameters η, are determined through density functional calculations. Clear correlations are established between 73Ge shifts and the mean of the four neighboring Ge-O-Ge bond angles, and between C Q and η parameters of 17O and the local Ge-O-Ge angle. Available experimental data for CQ and the corresponding established correlation are used to extract the value of 135° for the average Ge-O-Ge angle in vitreous GeO2. The features of the Ge-O-Ge bond angle distribution of vitreous GeO2 derived in this work are consistent with those inferred from other experimental probes. © 2010 IOP Publishing Ltd. Source


Vukajlovic F.R.,Vinca Institute of Nuclear Sciences | Popovic Z.S.,Vinca Institute of Nuclear Sciences | Baldereschi A.,Ecole Polytechnique Federale de Lausanne | Baldereschi A.,University of Trieste | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

By means of ab initio calculations based on density-functional theory we demonstrate that magnetism in monoatomic Fe wires deposited on nanostructured Ir(100) surface can be tuned by their functionalization with hydrogen. The pristine monoatomic Fe wires deposited on nanostructured Ir(100) surface partially covered by H atoms are antiferromagnetic. However, the type of exchange interaction between Fe atoms can be changed by increasing H coverage. At fully hydrogenated Ir surface the Fe wires themselves are decorated with hydrogen, which gives rise to the ferromagnetic coupling between adjacent Fe atoms. © 2010 The American Physical Society. Source


Lauchli A.M.,Max Planck Institute For Physik Komplexer Systeme | Lauchli A.M.,University of Innsbruck | Sudan J.,Institute Romand Of Recherche Numerique En Physique Des Materiaux Irrma | Sorensen E.S.,McMaster University
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We present a comprehensive list of the ground-state energies and the spin gaps of finite Kagomé clusters with up to 42 spins obtained using large-scale exact diagonalization techniques. This represents the current limit of this exact approach. For a fixed number of spins N, we study several cluster shapes under periodic boundary conditions in both directions resulting in a toroidal geometry. The clusters are characterized by their side length and diagonal as well as the shortest "Manhattan" diameter of the torii. A finite-size scaling analysis of the ground-state energy as well as the spin gap is then performed in terms of the shortest toroidal diameter as well as the shortest "Manhattan" diameter. The structure of the spin-spin correlations further supports the importance of short loops wrapping around the torii. © 2011 American Physical Society. Source


Yazyev O.V.,Ecole Polytechnique Federale de Lausanne | Yazyev O.V.,Institute Romand Of Recherche Numerique En Physique Des Materiaux Irrma | Yazyev O.V.,University of California at Berkeley | Pasquarello A.,Ecole Polytechnique Federale de Lausanne | Pasquarello A.,Institute Romand Of Recherche Numerique En Physique Des Materiaux Irrma
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Periodically corrugated epitaxial graphene and hexagonal boron nitride (h-BN) on metallic substrates are considered as perspective templates for the self-assembly of nanoparticles arrays. By using first-principles calculations, we determine binding energies and diffusion activation barriers of metal adatoms on graphene and h-BN. The observed chemical trends can be understood in terms of the interplay between charge transfer and covalent bonding involving the adatom d electrons. We further investigate the electronic effects of the metallic substrate and find that periodically corrugated templates based on graphene in combination with strong interactions at the metal/graphene interface are the most suitable for the self-assembly of highly regular nanoparticle arrays. © 2010 The American Physical Society. Source

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