24,359 research outputs found
Island formation without attractive interactions
We show that adsorbates on surfaces can form islands even if there are no
attractive interactions. Instead strong repulsion between adsorbates at short
distances can lead to islands, because such islands increase the entropy of the
adsorbates that are not part of the islands. We suggest that this mechanism
cause the observed island formation in O/Pt(111), but it may be important for
many other systems as well.Comment: 11 pages, 4 figure
Stuttering equivalence is too slow!
Groote and Wijs recently described an algorithm for deciding stuttering
equivalence and branching bisimulation equivalence, acclaimed to run in
time. Unfortunately, the algorithm does not always meet
the acclaimed running time. In this paper, we present two counterexamples where
the algorithms uses time. A third example shows that the
correction is not trivial. In order to analyse the problem we present
pseudocode of the algorithm, and indicate the time that can be spent on each
part of the algorithm in order to meet the desired bound. We also propose fixes
to the algorithm such that it indeed runs in time.Comment: 11 page
Ten-dimensional wave packet simulations of methane scattering
We present results of wavepacket simulations of scattering of an oriented
methane molecule from a flat surface including all nine internal vibrations. At
a translational energy up to 96 kJ/mol we find that the scattering is almost
completely elastic. Vibrational excitations when the molecule hits the surface
and the corresponding deformation depend on generic features of the potential
energy surface. In particular, our simulation indicate that for methane to
dissociate the interaction of the molecule with the surface should lead to an
elongated equilibrium C--H bond length close to the surface.Comment: RevTeX 15 pages, 3 eps figures: This article may be found at
http://link.aip.org/link/?jcp/109/1966
Energy dissipation and scattering angle distribution analysis of the classical trajectory calculations of methane scattering from a Ni(111) surface
We present classical trajectory calculations of the rotational vibrational
scattering of a non-rigid methane molecule from a Ni(111) surface. Energy
dissipation and scattering angles have been studied as a function of the
translational kinetic energy, the incidence angle, the (rotational) nozzle
temperature, and the surface temperature. Scattering angles are somewhat
towards the surface for the incidence angles of 30, 45, and 60 degree at a
translational energy of 96 kJ/mol. Energy loss is primarily from the normal
component of the translational energy. It is transfered for somewhat more than
half to the surface and the rest is transfered mostly to rotational motion. The
spread in the change of translational energy has a basis in the spread of the
transfer to rotational energy, and can be enhanced by raising of the surface
temperature through the transfer process to the surface motion.Comment: 8 pages REVTeX, 5 figures (eps
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