CNR Institute of Structure of Matter

Tito Scalo, Italy

CNR Institute of Structure of Matter

Tito Scalo, Italy
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Lazzeretti P.,CNR Institute of Structure of Matter
Journal of Molecular Spectroscopy | Year: 2017

Essential symmetry properties of physical quantities of classical mechanics and classical electromagnetism can be rationalized via the Abelian symmetry group GPT, with four operations (identity E, space inversion P, time reversal T, and combined PT) isomorphic to the spatial C2v point group. To account for charge conjugation C, a larger discrete group, GCPT, with eight operations (E,P,T,C, and their products, CP,CT,PT, and CPT), isomorphic to the spatial D2h point group, has been considered. Some features of these groups are discussed by a few examples, showing in particular that they provide group-theoretical implications for the existence of magnetic monopoles, magnetic scalar potential, magnetic charge density and magnetic current density, and magnetic-field induced electronic anapoles. A set of linearly independent vectors belonging to a representation space is constituted by eight fermion bilinears of quantum field theory. The GCPT group can be used to determine the discrete symmetry properties of molecular response tensors and provides interesting elucidations of established notions in a different, group-theoretical light, e.g., new understanding of duality transformations, which leave the Maxwell equations invariant, and a geometrical reinterpretation of Barron's concept of true enantiomers. © 2017.

Mattioli G.,CNR Institute of Structure of Matter | Giannozzi P.,University of Udine | Giannozzi P.,CNR Institute of Materials | Amore Bonapasta A.,CNR Institute of Structure of Matter | Guidoni L.,University of L'Aquila
Journal of the American Chemical Society | Year: 2013

The in-depth understanding of the molecular mechanisms regulating the water oxidation catalysis is of key relevance for the rationalization and the design of efficient oxygen evolution catalysts based on earth-abundant transition metals. Performing ab initio DFT+U molecular dynamics calculations of cluster models in explicit water solution, we provide insight into the pathways for oxygen evolution of a cobalt-based catalyst (CoCat). The fast motion of protons at the CoCat/water interface and the occurrence of cubane-like Co-oxo units at the catalyst boundaries are the keys to unlock the fast formation of O-O bonds. Along the resulting pathways, we identified the formation of Co(IV)-oxyl species as the driving ingredient for the activation of the catalytic mechanism, followed by their geminal coupling with O atoms coordinated by the same Co. Concurrent nucleophilic attack of water molecules coming directly from the water solution is discouraged by high activation barriers. The achieved results suggest also interesting similarities between the CoCat and the Mn 4Ca-oxo oxygen evolving complex of photosystem II. © 2013 American Chemical Society.

Cannuccia E.,University of Rome Tor Vergata | Cannuccia E.,European Theoretical Spectroscopy Facility | Marini A.,CNR Institute of Structure of Matter
Physical Review Letters | Year: 2011

The quantum zero-point motion of the carbon atoms is shown to induce strong effects on the optical and electronic properties of diamond and trans-polyacetylene, a conjugated polymer. By using an ab initio approach, we interpret the subgap states experimentally observed in diamond in terms of entangled electron-phonon states. These states also appear in trans-polyacetylene causing the formation of strong structures in the band structure that even call into question the accuracy of the band theory. This imposes a critical revision of the results obtained for carbon-based nanostructures by assuming the atoms frozen in their equilibrium positions. © 2011 American Physical Society.

In this work, we present a quantum mechanical scattering study of the title reaction from 1 mK to 2000 K. Total integral cross sections and thermal rate constants are compared with previous theoretical and experimental data and with simpler theoretical models to understand the range of validity of the approximations used in the previous studies. The obtained quantum reactive observables have been found to be nearly insensitive to the roto-vibrational energy of the reactants at high temperatures. More sensitive to the reactant's roto-vibrational energy are the data in the cold and ultra-cold regimes. The implications of the new data presented here in the early universe scenario are also discussed and analyzed. © 2014 the Partner Organisations.

Russina O.,University of Rome La Sapienza | Triolo A.,CNR Institute of Structure of Matter
Faraday Discussions | Year: 2012

The existence of a high degree of order over the mesoscopic spatial scale in room temperature ionic liquids is one of their most intriguing properties. Recently the possibility that such a feature, that is witnessed by the occurrence of peculiar low Q diffraction features, reflects nm-scale structural organization has been questioned on the basis of both experimental and computational studies. In this contribution we discuss these studies and present novel experimental evidence that confirm the existence of nm-scale spatial heterogeneities due to the segregation of apolar moieties dispersed in a polar network. The consequence of this scenario is that when the chain polarity gets closer to that of the charged head, the structural heterogeneities are no longer observed. © 2012 The Royal Society of Chemistry.

Filippone F.,CNR Institute of Structure of Matter
Journal of Physics Condensed Matter | Year: 2014

The free-standing, quasi-2D layer of Si is known as silicene, in analogy with graphene. Much effort is devoted in the study of silicene, since, similarly to graphene, it shows a very high electron mobility. The interaction of silicene with a hybrid substrate, β-Si3N4(0001)/Si(111), exposing the β-Si3N4(0001) surface, has been studied by means of Density Functional calculations, with van der Waals interactions included. Once deepened the most important structural and electronic features of the hybrid substrate, we demonstrated that an electron transfer occurs from the substrate to the silicene layer. In turn, such an electron transfer can be modulated by the doping of the substrate. The β-Si3N4/silicene interaction appears to be strong enough to ensure adequate adsorption stability. It is also shown that electronic states of substrate and adsorbate still remain decoupled, paving the way for the exploitation of the peculiar electron mobility properties of the silicene layer. A detailed analysis in both direct and reciprocal space is reported. © 2014 IOP Publishing Ltd.

Paparazzo E.,CNR Institute of Structure of Matter
Carbon | Year: 2013

This Letter discusses the X-ray photoelectron spectroscopy (XPS) results of an article on Pt and Pt-Sn nanoparticles dispersed on graphene nanosheets. I argue that the authors' interpretation is largely unwarranted because it neglects the spin-orbit multiplicity and the branching ratio of XPS signals arising from electron levels with l > 0, and the fact that XPS peaks of given electron levels and given chemical species possess precise full with at half maximum (FWHM) values, and binding energy (BE) values. I suggest an interpretation which offers a more accurate insight into the chemical composition and the catalytic properties of these nanoparticle systems. © 2013 Elsevier Ltd. All rights reserved.

Russina O.,University of Rome La Sapienza | Triolo A.,CNR Institute of Structure of Matter | Gontrani L.,CNR Institute of Structure of Matter | Caminiti R.,University of Rome La Sapienza
Journal of Physical Chemistry Letters | Year: 2012

Ionic liquids represent an exciting novel class of materials with potentially enormous applicative impact; they are proposed as environmentally responsible replacements for the noxious volatile organic solvents, as smart separation and catalysis media, or to develop electrochemical devices, just to mention a few examples. Recently, compelling experimental as well as computational evidence highlighted the complexity of RTIL morphology at the mesoscopic spatial scale, as compared to traditional molecular liquids. In this Perspective, we report on our current understanding on the nature of structural heterogeneities in ionic liquids, describing new experimental data supporting a microphase segregation structural model for these systems and proposing topics for further study. © 2011 American Chemical Society.

The carrier dynamics in bulk Silicon, a paradigmatic indirect gap semiconductor, is studied by using the Baym-Kadanoff equations. Both the electron-electron (e-e) and electron-phonon (e-p) self-energies are calculated fully ab-initio by using a semi-static out-of- equilibrium GW approximation in the e-e case and a Fan self-energy in the e-p case. By using the generalized Baym-Kadanoff ansatz the two-time evolution is replaced by the only dynamics on the macroscopic time axis. The enormous numerical difficulties connected with a real-time simulation of realistic systems is overcome by using a completed collision approximation that further simplifies the memory effects connected to the time evolution. The carrier dynamics is shown to reduce in such a way to have stringent connections to the well-known equilibrium electron-electron and electron-phonon self-energies. This link allows to use general arguments to motivate the relative balance between the e-e and e-p scattering channels on the basis of the carrier energies.

Flower-like silver nanoparticle superstructures are prepared by the reaction of silver nitrate and ascorbic acid in an acidic aqueous solution of a polynaphthalene system. The three-dimensional flower-like structure has a purely hierarchic arrangement, wherein each petal is composed of bundles of silver particle chains, each enclosed in a polymer sheath. The ordering arises from strong adsorption of silver ions onto the polymer and by the interplay of the redox properties of nitric and ascorbic acid. As a result, linear silver cyanide, formed on the polymer, probably due to intrinsic electric dipole fields, organizes the silver particle chains in dumbbell-like structures, resembling buds and flower-like structures. By dilution and heating of the mother liquors, it is also possible to obtain single petals, i.e. micrometer sized bundles of linearly aggregated silver nanoparticle chains, each enclosed in a polymer sheath.The comprehension of the hierarchic assembly of silver nanoparticles, paves the way to a facile general method to prepare polymer-metal nanoparticle chains and flower-like superstructures.The results of this study improve both the understanding of the formation mechanism of hierarchic structures at mild temperatures and our ability to tailor them to sizes and shapes appropriate for technological purposes.

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