3,959 research outputs found
On the Applicability of OGSA-BES to D-Grid Community Scheduling Systems
In this paper, we exemplary review the requirements of two Grid communities in the D-Grid project and identify similarities in the addressed scientific applications respectively. To facilitate Grid scheduler interoperability on the underlying heterogeneous middleware systems we extend the standardized OGSA-BES interface and propose a basic concept for the exploitation of collaboration potential in the D-Grid community in general. Compared with existing meta-scheduling architectures there will be no need for a central scheduler instance
Performance of dispersion-corrected density functional theory for thermochemistry and non-covalent interactions
Assessment of a variety of dispersion-corrected density functional theory calculations used in molecular crystal structure prediction
Accurate Treatment of Large Supramolecular Complexes by Double-Hybrid Density Functionals Coupled with Nonlocal van der Waals Corrections
In this work, we present a thorough assessment of the performance of some representative double-hybrid density functionals (revPBE0-DH-NL and B2PLYP-NL) as well as their parent hybrid and GGA counterparts, in combination with the most modern version of the nonlocal (NL) van der Waals correction to describe very large weakly interacting molecular systems dominated by noncovalent interactions. Prior to the assessment, an accurate and homogeneous set of reference interaction energies was computed for the supramolecular complexes constituting the L7 and S12L data sets by using the novel, precise, and efficient DLPNO-CCSD(T) method at the complete basis set limit (CBS). The correction of the basis set superposition error and the inclusion of the deformation energies (for the S12L set) have been crucial for obtaining precise DLPNO-CCSD(T)/CBS interaction energies. Among the density functionals evaluated, the double-hybrid revPBE0-DH-NL and B2PLYP-NL with the three-body dispersion correction provide remarkably accurate association energies very close to the chemical accuracy. Overall, the NL van der Waals approach combined with proper density functionals can be seen as an accurate and affordable computational tool for the modeling of large weakly bonded supramolecular systems.Financial support by the “Ministerio de Economía y Competitividad” (MINECO) of Spain and European FEDER funds through projects CTQ2011-27253 and CTQ2012-31914 is acknowledged. The support of the Generalitat Valenciana (Prometeo/2012/053) is also acknowledged. J.A. thanks the EU for the FP7-PEOPLE-2012-IEF-329513 grant. J.C. acknowledges the “Ministerio de Educación, Cultura y Deporte” (MECD) of Spain for a predoctoral FPU grant
Performance of ab initio and density functional methods for conformational equilibria of CnH2n+2 alkane isomers (n=2-8)
Conformational energies of n-butane, n-pentane, and n-hexane have been
calculated at the CCSD(T) level and at or near the basis set limit.
Post-CCSD(T) contribution were considered and found to be unimportant. The data
thus obtained were used to assess the performance of a variety of density
functional methods. Double-hybrid functionals like B2GP-PLYP and B2K-PLYP,
especially with a small Grimme-type empirical dispersion correction, are
capable of rendering conformational energies of CCSD(T) quality. These were
then used as a `secondary standard' for a larger sample of alkanes, including
isopentane and the branched hexanes as well as key isomers of heptane and
octane. Popular DFT functionals like B3LYP, B3PW91, BLYP, PBE, and PBE0 tend to
overestimate conformer energies without dispersion correction, while the M06
family severely underestimates GG interaction energies. Grimme-type dispersion
corrections for these overcorrect and lead to qualitatively wrong conformer
orderings. All of these functionals also exhibit deficiencies in the conformer
geometries, particularly the backbone torsion angles. The PW6B95 and, to a
lesser extent, BMK functionals are relatively free of these deficiencies.
Performance of these methods is further investigated to derive conformer
ensemble corrections to the enthalpy function, , and the Gibbs
energy function, , of these alkanes. While
is only moderately sensitive to the level of theory, exhibits more pronounced sensitivity. Once again, double hybrids
acquit themselves very well.Comment: J. Phys. Chem. A, revised [Walter Thiel festschrift
Adsorption of Cu, Ag, and Au atoms on graphene including van der Waals interactions
We performed a systematic density functional study of the adsorption of
copper, silver, and gold adatoms on graphene, especially accounting for van der
Waals interactions by the vdW-DF and the PBE+D2 methods. In particular, we
analyze the preferred adsorption site (among top, bridge, and hollow positions)
together with the corresponding distortion of the graphene sheet and identify
diffusion paths. Both vdW schemes show that the coinage metal atoms do bind to
the graphene sheet and that in some cases the buckling of the graphene can be
significant. The results for silver are at variance with those obtained with
GGA, which gives no binding in this case. However, we observe some quantitative
differences between the vdW-DF and the PBE+D2 methods. For instance the
adsorption energies calculated with the PBE+D2 method are systematically higher
than the ones obtained with vdW-DF. Moreover, the equilibrium distances
computed with PBE+D2 are shorter than those calculated with the vdW-DF method
Electric Field Enhanced Hydrogen Storage on BN Sheet
Using density functional theory we show that an applied electric field
substantially improves the hydrogen storage properties of a BN sheet by
polarizing the hydrogen molecules as well as the substrate. The adsorption
energy of a single H2 molecule in the presence of an electric field of 0.05
a.u. is 0.48 eV compared to 0.07 eV in its absence. When one layer of H2
molecules is adsorbed, the binding energy per H2 molecule increases from 0.03
eV in the field-free case to 0.14 eV/H2 in the presence of an electric field of
0.045 a.u. The corresponding gravimetric density of 7.5 wt % is consistent with
the 6 wt % system target set by DOE for 2010. Once the applied electric field
is removed, the stored H2 molecules can be easily released, thus making the
storage reversible.Comment: submitted to Phys. Rev. Lett. 15 pages with 6 figure
Meta-analysis of Individual Patient Data After Kissing Stent Treatment for Aortoiliac Occlusive Disease
Direct observation of a highly spin-polarized organic spinterface at room temperature
The design of large-scale electronic circuits that are entirely
spintronics-driven requires a current source that is highly spin-polarised at
and beyond room temperature, cheap to build, efficient at the nanoscale and
straightforward to integrate with semiconductors. Yet despite research within
several subfields spanning nearly two decades, this key building block is still
lacking. We experimentally and theoretically show how the interface between Co
and phthalocyanine molecules constitutes a promising candidate. Spin-polarised
direct and inverse photoemission experiments reveal a high degree of spin
polarisation at room temperature at this interface. We measured a magnetic
moment on the molecules's nitrogen pi orbitals, which substantiates an
ab-initio theoretical description of highly spin-polarised charge conduction
across the interface due to differing spinterface formation mechanims in each
spin channel. We propose, through this example, a recipe to engineer simple
organic-inorganic interfaces with remarkable spintronic properties that can
endure well above room temperature
Novel techniques for weak alignment of proteins in solution using chemical tags coordinating lanthanide ions
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