52,814 research outputs found
Cohesion of BaReH and BaMnH: Density Functional Calculations and Prediction of (MnH Salts
Density functional calculations are used to calculate the structural and
electronic properties of BaReH and to analyze the bonding in this compound.
The high coordination in BaReH is due to bonding between Re 5 states and
states of -like symmetry formed from combinations of H orbitals in the
H cage. This explains the structure of the material, its short bond lengths
and other physical properties, such as the high band gap. We compare with
results for hypothetical BaMnH, which we find to have similar bonding and
cohesion to the Re compound. This suggests that it may be possible to
synthesize (MnH salts. Depending on the particular cation, such salts
may have exceptionally high hydrogen contents, in excess of 10 weight
The Band Gap in Silicon Nanocrystallites
The gap in semiconductor nanocrystallites has been extensively studied both
theoretically and experimentally over the last two decades. We have compared a
recent ``state-of-the-art'' theoretical calculation with a recent
``state-of-the-art'' experimental observation of the gap in Si nanocrystallite.
We find that the two are in substantial disagreement, with the disagreement
being more pronounced at smaller sizes. Theoretical calculations appear to
over-estimate the gap. Recognizing that the experimental observations are for a
distribution of crystallite sizes, we proffer a phenomenological model to
reconcile the theory with the experiment. We suggest that similar
considerations must dictate comparisons between the theory and experiment
vis-a-vis other properties such as radiative rate, decay constant, absorption
coefficient, etc.Comment: 5 pages, latex, 2 figures. (Submitted Physical Review B
Electronic Structure and Thermoelectric Prospects of Phosphide Skutterudites
The prospects for high thermoelectric performance in phosphide skutterudites
are investigated based on first principles calculations. We find that
stoichiometric CoP_3 differs from the corresponding arsenide and antimonide in
that it is metallic. As such the band structure must be modified if high
thermopowers are to be achieved. In analogy to the antimonides it is expected
that this may be done by filling with La. Calculations for LaFe_4P_12 show that
a gap can in fact be opened by La filling, but that the valence band is too
light to yield reasonable p-type thermopowers at appropriate carrier densities;
n-type La filled material may be more favorable.Comment: 3 pages, 3 figures, 1 tabl
Hydrodynamic signatures of stationary Marangoni-driven surfactant transport
We experimentally study steady Marangoni-driven surfactant transport on the
interface of a deep water layer. Using hydrodynamic measurements, and without
using any knowledge of the surfactant physico-chemical properties, we show that
sodium dodecyl sulphate and Tergitol 15-S-9 introduced in low concentrations
result in a flow driven by adsorbed surfactant. At higher surfactant
concentration, the flow is dominated by the dissolved surfactant. Using
Camphoric acid, whose properties are {\it a priori} unknown, we demonstrate
this method's efficacy by showing its spreading is adsorption dominated
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