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Ab Initio Simulation (ab + initio_simulation)
Selected AbstractsAb initio Simulation of Lewis Sites in Mordenite and Comparative Study of the Strength of Active Sites via CO Adsorption.CHEMINFORM, Issue 45 2004L. Benco No abstract is available for this article. [source] Ab initio simulations of accretion disc instabilityMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2004V. Teresi ABSTRACT We show that accretion discs, both in the subcritical and supercritical accretion rate regime, may exhibit significant amplitude luminosity oscillations. The luminosity time behaviour has been obtained by performing a set of time-dependent two-dimensional smoothed particle hydrodynamics simulations of accretion discs with different values of , and accretion rate. In this study, to avoid any influence of the initial disc configuration, we produced the discs injecting matter from an outer edge far from the central object. The period of oscillations is 2,50 s for the two cases, and the variation amplitude of the disc luminosity is 1038,1039 erg s,1. An explanation of this luminosity behaviour is proposed in terms of limit cycle instability; the disc oscillates between a radiation pressure dominated configuration (with a high luminosity value) and a gas pressure dominated one (with a low luminosity value). The origin of this instability is the difference between the heat produced by viscosity and the energy emitted as radiation from the disc surface (the well-known thermal instability mechanism). We support this hypothesis showing that the limit cycle behaviour produces a sequence of collapsing and refilling states of the innermost disc region. [source] Thermochemistry and Crystal Structure of Lithium, Sodium and Potassium Alanates as Determined by ab initio Simulations.CHEMINFORM, Issue 30 2004Sai-Cheong Chung No abstract is available for this article. [source] An ab initio simulation of the UV/visible spectra of N -benzylideneaniline dyesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2009Denis Jacquemin Abstract The structural parameters and the absorption spectra of more than thirty N -benzylideneaniline dyes have been determined with a theoretical scheme combining the time-dependent density functional theory and the polarizable continuum model. For the unsubstituted molecule, the PBE0 hybrid nicely reproduces both the measured structural parameters and the absorption spectrum, and we demonstrate that the nature of the two first transitions is reversed compared with azobenzene. For the set of substituted compounds, the average TD-DFT error (0.19 eV), that can be significantly reduced by a simple statistical treatment, mainly originates in the charge-transfer states of push,pull derivatives, whereas local transitions are accurately modeled. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Efficient and reliable method for the simulation of scanning tunneling images and spectra with local basis setsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2006Óscar Paz Abstract Based on Bardeen's perturbative approach to tunneling, we have found an expression for the current between tip and sample, which can be efficiently coded in order to perform fast ab initio simulations of STM images. Under the observation that the potential between the electrodes should be nearly flat at typical tunnel gaps, we have addressed the difficulty in the computation of the tunneling matrix elements by considering a vacuum region of constant potential delimited by two surfaces (each of them close to tip and sample respectively), then propagating tip and sample wave functions by means of the vacuum Green's function, to finally obtain a closed form in terms of convolutions. The current is then computed for every tip-sample relative position and for every bias voltage in one shot. The electronic structure of tip and sample is calculated at the same footing, within density functional theory, and independently. This allows us to carry out multiple simulations for a given surface with a database of different tips. We have applied this method to the Si(111)-(7 × 7) and Ge(111)- c (2 × 8) surfaces. Topographies and spectroscopic data, showing a very good agreement with experiments, are presented. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||