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A Beccara S.,University of Trento | Garberoglio G.,University of Trento | Garberoglio G.,Center for Materials and Microsystems | Faccioli P.,University of Trento | Pederiva F.,University of Trento
Journal of Chemical Physics | Year: 2010

We introduce a framework to investigate ab initio the dynamics of rare thermally activated reactions, which cannot be studied using the existing techniques. The electronic degrees of freedom are described at the quantum-mechanical level in the Born-Oppenheimer approximation, while the nuclear degrees of freedom are coupled to a thermal bath, through a classical Langevin equation. This method is based on the path integral representation for the stochastic dynamics and yields the time evolution of both nuclear and electronic degrees of freedom, along the most probable reaction pathways, without spending computational time to explore metastable states. As a first illustrative application, we characterize the dominant pathway in the cyclobutene→butadiene reaction, using the semiempirical Parametrized Model 3 (PM3) approach. © 2010 American Institute of Physics.

Lukowiak A.,CNR Institute for Photonics and Nanotechnologies | Lukowiak A.,Institute of Low Temperature And Structure Research | Wiglusz R.J.,Institute of Low Temperature And Structure Research | Chiappini A.,CNR Institute for Photonics and Nanotechnologies | And 6 more authors.
Journal of Non-Crystalline Solids | Year: 2014

Nanoparticles of lithium lanthanum tetraphosphates doped with different concentration of Eu3 + ions were synthesized. The selected tetraphosphate was used to fabricate a transparent composite where nanocrystals were immobilized in a sol-gel-derived silica-hafnia amorphous film. The structural and spectroscopic properties of the systems were investigated by XRD analysis, Raman spectroscopy, and photoluminescence measurements. For all the samples with the Eu3 + ions concentration from 1 to 100 mol% the monoclinic structure with a space group C12/c1 was determined. The mean diameter of nanocrystals determined by Scherrer equation was in the range of 40-55 nm. The luminescence of 10%Eu3 +:LiLa(PO3)4 in silica-hafnia matrix indicated the immobilization of Eu3 + ions into a distorted environment. The dependence of both luminescence intensity and lifetime on the Eu3 + concentration demonstrated effective reduction of concentration quenching in the tetraphosphate nanopowders. © 2013 Elsevier B.V.

Ciappa M.,ETH Zurich | Koschik A.,ETH Zurich | Dapor M.,Center for Materials and Microsystems | Fichtner W.,ETH Zurich
Microelectronics Reliability | Year: 2010

Modeling of critical dimensions scanning electron microscopy with sub-nanometer uncertainty is required to provide a metrics and to avoid yield loss in the processing of advanced CMOS technologies. In this paper, a new approach is proposed, which includes a new Monte Carlo scheme, a new Monte Carlo code, as well as the coupling with electrostatic fields to take into account self-charging effects. © 2010 Elsevier Ltd. All rights reserved.

Jedlovszky P.,Eotvos Lorand University | Jedlovszky P.,HAS Research Group of Technical Analytical Chemistry | Garberoglio G.,University of Trento | Garberoglio G.,Consorzio Nazionale Interuniversitario per le Science Fisiche della Materia | And 2 more authors.
Journal of Physics Condensed Matter | Year: 2010

We report results of molecular dynamics simulations of supercooled bulk water at 180 K, close to the liquid/liquid coexistence lines recently discovered in the supercooled regime, both experimentally and by computer simulations. Despite the considerable differences in the densities of the three states considered, the obtained velocity autocorrelation functions display very similar behaviour in every case. On the other hand, the corresponding spectra show the presence of three well-defined modes. The two modes at higher frequencies are assigned to the symmetric and asymmetric stretching motions, respectively, whereas the lowest frequency mode to the bending and torsional motions in clusters of five hydrogen-bonded water molecules. A careful fitting procedure demonstrates the presence of such clusters also in the normal liquid phase of water at ambient conditions. © 2010 IOP Publishing Ltd.

Garberoglio G.,University of Trento | Garberoglio G.,University of Pittsburgh | Garberoglio G.,U.S. National Energy Technology Laboratory | Garberoglio G.,Center for Materials and Microsystems | And 2 more authors.
ACS Nano | Year: 2010

The effect of the quantized rotational degrees of freedom of hydrogen on the adsorption and sieving properties in carbon nanotubes is studied using computer simulations. We have developed a highly efficient multiple timestep algorithm for hybrid Monte Carlo sampling of quantized rotor configurations and extended the grand canonical Boltzmann bias method to rigid linear molecules. These new computational tools allow us to calculate accurately the quantum sieving selectivities for cases of extreme two-dimensional confinement as a function of pressure. The para-T2/para-H2 selectivity at 20 K is analyzed as a function of the tube diameter and the density of adsorbed hydrogen. Extraordinarily high selectivities, up to 2.6 × 108, are observed in the narrowest nanotube. The quantized nature of the rotational degrees of freedom is found to dramatically affect adsorption and selectivity for hydrogen isotopes adsorbed in very narrow nanotubes. The T 2/H2 zero-pressure selectivity increases from 2.4 × 104 to 1.7 × 108 in the (3,6) nanotube at 20 K when quantum rotations are accounted for. The isotopic selectivity is found to increase with pressure, tending to a constant value at saturation. A simplified mean-field model is used to discuss the origin of this behavior. © 2010 American Chemical Society.

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