Teraflop 73 - Novembre - cesca

Figure 1
Figure 3
Figure 4
Figure 1. A sequence of atomic
configurations (starting from the
top left corner and going from
left to right in each row), taken
from room-temperature molecular
dynamics simulations (see
Ref.1 a), predicting the formation
of a gold nanowire through the
elongation of the contact between
a nickel tip (red atoms) and a
gold surface (the topmost layer
in yellow, the second layer in
blue, and so on).
Figure 2. Atomic configurations
taken from molecular dynamics
simulations (see Ref. 2), illustrating
layering of liquid hexadecane
(green) confined by: top —a
nickel tip (gray) and a gold surface
(yellow); middle —two parallel
gold surfaces; bottom —two
gold surfaces with pyramidal nanostructures.
Figure 3. Atomic configurations
taken from molecular dynamics
simulations (see Ref. 2), illustrating
layering of liquid hexadecane
(green) confined by: top —a
nickel tip (gray) and a gold surface
(yellow); middle —two parallel
gold surfaces; bottom —two
gold surfaces with pyramidal nanostructures.
Frames (A-C): atomic
configurations taken from
molecular dynamics (MD) simulations
(see Ref. 3), illustrating
breakup scenarios of a droplet
from a nanojet made of propane
molecules (in blue). The geometry
of the most often occurring
break-up configuration,
with two cones joined at their
apices, is depicted in (B). The results
shown in frame (D) correspond
to: top —a coarse-grained
illustration of the MD result;
middle —configuration obtained
from a deterministic hydrodynamic
formulation (that is, the lubrication
equation – LE), exhibiting
the development of an elongated
thread that is not found in
the MD simulations; bottom —
configuration corresponding to
the stochastic hydrodynamic formulation
(SLE), illustrating that
the incorporation of stochastic
fluctuations in the hydrodynamic
continuum description leads to
close correspondence with the
atomistic MD result.
Figure 4. Electronic properties
and nanocatalytic activity of negatively
charged Aun clusters,
made of n = 16, 17, 18, 19, and
20 atoms, left to right, respectively
(B. Yoon, H. Hakkinen, U.
Landman, to be published). The
blue dots correspond to results
obtained through density-func-
Figure 2
Figure 5
tional theory calculations of the
vertical detachment energy (vDE
– the energy to remove the excess
electron), and the values
marked by X represent measured
results. Also shown are the
optimal structures of the clusters,
with superimposed contour
surfaces of the highest-occupied-molecular-orbital
(HOMO)
occupied by the excess electron.
The anion cluster with 20
gold atoms is characterized by
localization of the excess electronic
charge at the low-coordination
corner sites, and by the
lowest detachment energy. These
properties correlate with a
predicted high catalytic activity
of the cluster in the oxidation of
carbon monoxide by oxygen leading
to formation of carbon dioxide.
In contrast, in the gold
cluster anion with n=16 the ex-
TERAFLOP
Novembre 2003
cess electron is delocalized and
the vDE is relatively high, resulting
in absence of catalytic activity.
Figure 5. Trajectory of a sodium
counterion (purple) is
shown superimposed on a short
nucleobase sequence of DNA.
The trajectory is taken from a
1.6 nano-second MD simulation,
and it illustrates the high mobility
of the counterions. In the simulation
the seven base-pair duplex
DNA sequence was immersed in
water with 12 sodium counterions.
Configurations obtained
from the MD simulations were
used in density-functional calculations
of the properties of ionization
holes in DNA, leading to
formulation of an ion-gating model
for the migration of such holes
in DNA, see Ref. 5.