8,673 research outputs found
To Wet or Not to Wet? Dispersion Forces Tip the Balance for Water Ice on Metals
Despite widespread discussion, the role of van der Waals dispersion forces in wetting remains unclear. Here we show that nonlocal correlations contribute substantially to the water-metal bond and that this is an important factor in governing the relative stabilities of wetting layers and 3D bulk ice. Because of the greater polarizability of the substrate metal atoms, nonlocal correlations between water and the metal exceed those between water molecules within ice. This sheds light on a long-standing problem, wherein common density functional theory exchange-correlation functionals incorrectly predict that none of the low temperature experimentally characterized icelike wetting layers are thermodynamically stable
Multiple merging in the Abell cluster 1367
We present a dynamical analysis of the central ~1.3 square degrees of the
cluster of galaxies Abell 1367, based on 273 redshift measurements (of which
119 are news). From the analysis of the 146 confirmed cluster members we derive
a significantly non-Gaussian velocity distribution, with a mean location C_{BI}
= 6484+/-81 km/s and a scale S_{BI} = 891+/-58 km/s. The cluster appears
elongated from the North-West to the South-East with two main density peaks
associated with two substructures. The North-West subcluster is probably in the
early phase of merging into the South-East substructure (~ 0.2 Gyr before core
crossing). A dynamical study of the two subclouds points out the existence of a
group of star-forming galaxies infalling into the core of the South-East
subcloud and suggests that two other groups are infalling into the NW and SE
subclusters respectively. These three subgroups contain a higher fraction of
star-forming galaxies than the cluster core, as expected during merging events.
Abell 1367 appears as a young cluster currently forming at the intersection of
two filaments.Comment: 15 pages, 13 figures, 7 tables. Accepted for publication on A&A. High
resolution figures at http://goldmine.mib.infn.it/papers/a1367.htm
The Radio Jet Associated with the Multiple V380 Ori System
The giant Herbig-Haro object 222 extends over 6 in the plane of the
sky, with a bow shock morphology. The identification of its exciting source has
remained uncertain over the years. A non-thermal radio source located at the
core of the shock structure was proposed to be the exciting source. However,
Very Large Array studies showed that the radio source has a clear morphology of
radio galaxy and a lack of flux variations or proper motions, favoring an
extragalactic origin. Recently, an optical-IR study proposed that this giant HH
object is driven by the multiple stellar system V380 Ori, located about 23
to the SE of HH 222. The exciting sources of HH systems are usually detected as
weak free-free emitters at centimeter wavelengths. Here we report the detection
of an elongated radio source associated with the Herbig Be star or with its
close infrared companion in the multiple V380 Ori system. This radio source has
the characteristics of a thermal radio jet and is aligned with the direction of
the giant outflow defined by HH~222 and its suggested counterpart to the SE,
HH~1041. We propose that this radio jet traces the origin of the large scale HH
outflow. Assuming that the jet arises from the Herbig Be star, the radio
luminosity is a few times smaller than the value expected from the
radio-bolometric correlation for radio jets, confirming that this is a more
evolved object than those used to establish the correlation.Comment: 13 pages, 3 figure
Insight into the description of van der Waals forces for benzene adsorption on transition metal (111) surfaces
Exploring the role of van der Waals (vdW) forces on the adsorption of
molecules on extended metal surfaces has become possible in recent years thanks
to exciting developments in density functional theory (DFT). Among these newly
developed vdW-inclusive methods, interatomic vdW approaches that account for
the nonlocal screening within the bulk [V. G. Ruiz, W. Liu, E. Zojer, M.
Scheffler, and A. Tkatchenko, Phys. Rev. Lett. 108, 146103 (2012)] and improved
nonlocal functionals [J. Klimes, D. R. Bowler, and A. Michaelides, J. Phys.:
Condens. Matter 22, 022201(2010)] have emerged as promising candidates to
account efficiently and accurately for the lack of long-range vdW forces in
most popular DFT exchange-correlation functionals. Here we have used these two
approaches to compute benzene adsorption on a range of close-packed (111)
surfaces upon which it either physisorbs (Cu, Ag, and Au) or chemisorbs (Rh,
Pd, Ir, and Pt). We have thoroughly compared the performance between the two
classes of vdW-inclusive methods and when available compared the results
obtained with experimental data. By examining the computed adsorption energies,
equilibrium distances, and binding curves we conclude that both methods allow
for an accurate treatment of adsorption at equilibrium adsorbate-substrate
distances. To this end, explicit inclusion of electrodynamic screening in the
interatomic vdW scheme and optimized exchange functionals in the case of
nonlocal vdW density functionals is mandatory. Nevertheless, some discrepancies
are found between these two classes of methods at large adsorbate-substrate
separations
- …