374 research outputs found
Shell Structure of Cesium Layer Covering the C60 Fullerene Core
Strutinsky shell corrections for the Cesium-coated fullerenes were
investigated. The single particle levels of electrons are obtained using the
spherical mean-field potential of a shifted Wood-Saxon type. The parameters of
the potential are adjusted to reproduce the experimental ionization energies of
the Cs(N) clusters and the magic numbers observed in their photo-ionization
spectra of the C60Cs(N) aggregates.Comment: 6 pages in LaTex, 7 eps figure
Mean first passage time for nuclear fission and the emission of light particles
The concept of a mean first passage time is used to study the time lapse over
which a fissioning system may emit light particles. The influence of the
"transient" and "saddle to scission times" on this emission are critically
examined. It is argued that within the limits of Kramers' picture of fission no
enhancement over that given by his rate formula need to be considered.Comment: 4 pages, RevTex, 4 postscript figures; with correction of misprints;
appeared in Phys. Rev. Lett.90.13270
First-principles investigation of carbon nanotube capacitance
With ab initio simulations based on a real-space nonequilibrium Green’s function formalism, we have investigated the charging of carbon nanotube systems. The charging effects are described by capacitance coefficients, for which we provide a first-principles estimate. Specifically, the capacitance matrix of nested armchair nanotubes, the insertion of one nanotube into another, and a junction of two metallic nanotubes with a large conductance gap were calculated with a focus on investigating the bias-induced charges. For the case of the nanotube junction, the numerical value of the capacitance is sufficiently high, as to be useful for future device applications.published_or_final_versio
Self-consistent analysis of a quantum capacitor
We analyze the behavior of the magnetocapacitance for a three-probe capacitor. The self-consistent evaluation of the internal potential is found to play a large role in determining quantitative values of the capacitance. For capacitor plates of mesoscopic size, this potential reduces the charge accumulation by more than an order of magnitude compared to that obtained with noninteracting models. However, the qualitative behavior of the magnetocapacitance is not substantially altered by the self-consistency. A simple but physically motivated model gives an analytical formula which compares well with the numerical data.published_or_final_versio
Capacitance, induced charges, and bound states of biased carbon nanotube systems
Although it has long been known that the classical notions of capacitance need modification at the nanoscale, in order to account for important quantum effects, very few first-principles investigations of these properties exist for any real material systems. Here we present the results of a large-scale ab initio investigation of the capacitance properties of carbon nanotube systems. The simulations are based on a recently developed real-space nonequilibrium Green's-function approach, with special attention being paid to the treatment of the bound states present in the system. In addition, use has been made of a symmetry decomposition scheme for the charge density. This is needed both to speed up the calculations and in order to study the origins of the induced charges. Specific systems investigated include two and three nested nanotube shells, the insertion of a capped nanotube into another, a connected (12,0)/(6,6) nanotube junction, and the properties of a nanotube acting as a probe over a flat aluminum surface. First-principles estimates of the capacitance matrix coefficients for all these systems are provided, along with a discussion of the quantum corrections. For the case of the nanotube junction, the numerical value of the capacitance is sufficiently high, as to be useful for future device applications.published_or_final_versio
Stability of bubble nuclei through Shell-Effects
We investigate the shell structure of bubble nuclei in simple
phenomenological shell models and study their binding energy as a function of
the radii and of the number of neutron and protons using Strutinsky's method.
Shell effects come about, on the one hand, by the high degeneracy of levels
with large angular momentum and, on the other, by the big energy gaps between
states with a different number of radial nodes. Shell energies down to -40 MeV
are shown to occur for certain magic nuclei. Estimates demonstrate that the
calculated shell effects for certain magic numbers of constituents are probably
large enough to produce stability against fission, alpha-, and beta-decay. No
bubble solutions are found for mass number A < 450.Comment: 9 pages and 9 figures in the eps format include
Effect of differences in proton and neutron density distributions on fission barriers
The neutron and proton density distributions obtained in constrained
Hartree-Fock-Bogolyubov calculations with the Gogny force along the fission
paths of 232Th, 236U, 238U and 240Pu are analyzed.
Significant differences in the multipole deformations of neutron and proton
densities are found. The effect on potential energy surfaces and on barrier
heights of an additional constraint imposing similar spatial distributions to
neutrons and protons, as assumed in macroscopic-microscopic models, is studied.Comment: 5 pages in Latex, 4 figures in ep
Comment on ``Passage Times for Unbiased Polymer Translocation through a Narrow Pore''
One of the most fundamental quantities associated with polymer translocation
through a nanopore is the translocation time and its dependence on the
chain length . Our simulation results based on both the bond fluctuation
Monte Carlo and Molecular Dynamics methods confirm the original prediction
, which scales in the same manner as the Rouse relaxation
time of the chain except for a larger prefactor, and invalidates other scaling
claims.Comment: 1+pages, 1 Figure, Minor change
Contact-induced spin polarization in carbon nanotubes
Motivated by the possibility of combining spintronics with molecular
structures, we investigate the conditions for the appearance of
spin-polarization in low-dimensional tubular systems by contacting them to a
magnetic substrate. We derive a set of general expressions describing the
charge transfer between the tube and the substrate and the relative energy
costs. The mean-field solution of the general expressions provides an
insightful formula for the induced spin-polarization. Using a tight-binding
model for the electronic structure we are able to estimate the magnitude and
the stability of the induced moment. This indicates that a significant magnetic
moment in carbon nanotubes can be observed.Comment: To appear in Phys. Rev. B (2003
- …