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Ping Y.,University of California at Davis | Rocca D.,University of California at Davis | Rocca D.,University of Lorraine | Rocca D.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling | Galli G.,University of California at Davis
Chemical Society Reviews | Year: 2013

We describe state of the art methods for the calculation of electronic excitations in solids and molecules, based on many body perturbation theory, and we discuss some applications of these methods to the study of band edges and absorption processes in representative materials used as photoelectrodes for water splitting. © 2013 The Royal Society of Chemistry.


Vila N.,CNRS Laboratory of Physical Chemistry and Microbiology for the Environment | Ghanbaja J.,CNRS Jean Lamour Institute | Aubert E.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling | Walcarius A.,CNRS Laboratory of Physical Chemistry and Microbiology for the Environment
Angewandte Chemie - International Edition | Year: 2014

One key challenge in inorganic mesoporous films is the development of oriented mesostructures with vertical channels, and even more challenging is their functionalization while maintaining accessible the selected surface groups. Combining the electrochemically assisted deposition of ordered and oriented azide-functionalized mesoporous silica with alkyne-azide click chemistry enables such nanostructured and vertically aligned hybrid films to be obtained with significant amounts of active organic functional groups, as illustrated for ferrocene and pyridine functions. A good level of mesostructural order was obtained, namely up to 40 % of organosilane in the starting sol. The method could be applied to a wide variety of functional groups, thus offering numerous new opportunities for applications in various fields. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Lebegue S.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling | Harl J.,University of Vienna | Gould T.,Griffith University | Angyan J.G.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling | And 2 more authors.
Physical Review Letters | Year: 2010

The structural properties of graphite, such as the interlayer equilibrium distance, the elastic constant, and the net layer binding energy, are obtained using the adiabatic-connection fluctuation-dissipation theorem in the random phase approximation. Excellent agreement is found with the available experimental data; however, our computed binding energy of 48 meV per atom is somewhat smaller than the one obtained by quantum Monte Carlo methods. The asymptotic behavior of the interlayer dispersion interaction, previously derived from analytic approximations, is explicitly demonstrated to follow a d⊃-3 behavior at very large distances. © 2010 The American Physical Society.


Bucko T.,Comenius University | Bucko T.,Slovak Academy of Sciences | Lebegue S.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling | Hafner J.,University of Vienna | Angyan J.G.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

The method proposed by Tkatchenko and Scheffler to correct density functional calculations for the missing van der Waals interactions is implemented in the Vienna ab initio simulation package (vasp) code and tested on a wide range of solids, including noble-gas crystals, molecular crystals (α-N2, sulfur dioxide, benzene, naphthalene, cytosine), layered solids (graphite, hexagonal boron nitride, vanadium pentoxide, MoS2, NbSe2), chain-like structures (selenium, tellurium, cellulose I), ionic crystals (NaCl, KI), and metals (nickel, zinc, cadmium). In addition to the original formulation expressing the van der Waals (vdW) corrections as pairwise potentials whose strength is derived from the rescaled polarizabilities of the neutral free atoms, the self-consistently screened (TS+SCS) variant of the method involving electrodynamic response effects has been examined. Analytical expressions for the forces acting on the atoms and for the components of the stress tensor needed for the relaxation of the volume and shape of the unit cell using the TS+SCS method are derived. While the calculated structures are reasonably close to experiment, the van der Waals corrections to the binding energies are often found to be overestimated in comparison with experimental data. The TS+SCS approach leads to significantly better results in some problematic cases, such as the binding energy of graphite. However, there is room for further improvements, in particular for strongly ionic systems. © 2013 American Physical Society.


Lebegue S.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling | Bjorkman T.,Aalto University | Klintenberg M.,Uppsala University | Nieminen R.M.,Aalto University | Eriksson O.,Uppsala University
Physical Review X | Year: 2013

Progress in materials science depends on the ability to discover new materials and to obtain and understand their properties. This has recently become particularly apparent for compounds with reduced dimensionality, which often display unexpected physical and chemical properties, making them very attractive for applications in electronics, graphene being so far the most noteworthy example. Here, we report some previously unknown two-dimensional materials and their electronic structure by data mining among crystal structures listed in the International Crystallographic Structural Database, combined with density-functional-theory calculations. As a result, we propose to explore the synthesis of a large group of two-dimensional materials, with properties suggestive of applications in nanoscale devices, and anticipate further studies of electronic and magnetic phenomena in low-dimensional systems.


Angyan J.G.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling
Current Organic Chemistry | Year: 2011

The concept of localization and delocalization in molecules is discussed in terms of the response of the electronic system to an external perturbation. It is argued that both the spatial organization of electrons in pairs and the spatial distribution of the response intensity, reflect main features of the correlated motion of electrons, ultimately described by the pair distribution function of electrons. Various measures, derived from the linear charge density response function, are able to characterize localization in a rigorous way, in close analogy to the approach followed in solid state physics. © 2011 Bentham Science Publishers.


Nicolazzi W.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling | Nicolazzi W.,CNRS Coordination Chemistry | Pillet S.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We present a nonequilibrium study of the relaxation process in spin crossover solids using numerical simulations of a recently introduced two-variable elastic Ising-like model. We analyze the structural lattice distortions accompanying the relaxation from the metastable high-spin to the ground low-spin state as a function of cooperativity. In the highly cooperative case, a sigmoidal relaxation behavior of the high-spin fraction n HS is described, and it occurs jointly with a structural phase separation process. The mean lattice spacing follows a similar sigmoidal trend, owing to the interplay between electronic and lattice variables in the Hamiltonian. Weakly cooperative systems are characterized by single exponential relaxations of the high-spin fraction, the corresponding structural transformation proceeds homogeneously with a progressive relaxation of the mean lattice spacing. Long relaxation tail effects are also observed. We highlight the development of lattice strain accompanying the spin transition, and show that structural phase rebuilding proceeds in the late stage of the relaxation by releasing residual strain. Under specific conditions, a temporal decoupling between the electronic and lattice variables is observed, which may have direct applications for interpreting time-resolved spectroscopic or diffraction experiments and for elucidating unusual structural behaviors, such as the development of superstructures, modulated structures, or transient phases. © 2012 American Physical Society.


Mata I.,CSIC - Institute of Materials Science | Alkorta I.,Institute Quimica Medica IQM CSIC | Molins E.,CSIC - Institute of Materials Science | Espinosa E.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling
Chemistry - A European Journal | Year: 2010

Topological analyses of the theoretically calculated electron densities for a large set of 163 hydrogenbonded complexes show that H··· X interactions can be classified in families according to X (X=atom or π orbital). Each family is characterised by a set of intrinsic dependencies between the topological and energetic properties of the electron density at the hydrogenbond critical point, as well as between each of them and the bonding distance. Comparing different atom-acceptor families, these dependencies are classified as a function of the van der Waals radius rX or the electronegativity χX, which can be explained in terms of the molecular orbitals involved in the interaction. According to this ordering, the increase of χX leads to a larger range of H···X distances for which the interaction is of pure closed-shell type. Same dependencies observed for H···O interactions experimentally characterised by means of high-resolution X-ray diffraction data show a good agreement with those obtained from theoretical calculations, in spite of a larger dispersion of values around the expected fitting functions in the experimental case. Theoretical dependencies can thus be applied to the analysis of the experimental electron density for detecting either unconventional hydrogen bonds or problems in the modelling of the experimental electron density. © 2010 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.


Nespolo M.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling
Journal of Applied Crystallography | Year: 2015

Normalizers of space groups are extensively used in the solution of diverse tasks in structural crystallography. Yet, they are often considered an 'esoteric' topic, seldom introduced in the education curriculum of a crystallographer. This paper presents a pedagogical introduction with special emphasis on their role in the equivalent description of crystal structures. © 2015 International Union of Crystallography.


Debbichi L.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling | Debbichi L.,Uppsala University | Eriksson O.,Uppsala University | Lebegue S.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

By means of first-principles GW calculations, we have studied the electronic structure properties of MX2 (M=Mo, W; X=S, Se, Te) bilayers, including hybrid structures of MX2 building blocks. The effect of spin-orbit coupling on the electronic structure and the effect of van der Waals interaction on the geometry were taken into account. All the homogeneous bilayers are identified as indirect band-gap materials, with an increase of the band gap when Mo is changed to W, and a decrease of the band gap when the atomic number of X is increased. The same behavior is also observed for hybrid bilayers with common chalcogen atoms, while bilayers with common metal atoms have a direct band gap. Finally, it is shown that due to their particular band alignment, some heterobilayers enable electron-hole separation, which is of interest for solar cell applications. © 2014 American Physical Society.

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