116 research outputs found
Comment to "Imaging the atomic orbitals of carbon atomic chains with field-emission electron microscopy"
The observation of a stable doublet pattern in the field-emission electron
microscopy of a linear atomic chain requires a stable mechanism breaking the
axial symmetry, which is not identified correctly by Mikhailovskij et al.
[Phys. Rev. B 80, 165404 (2009)]. Using microscopic calculations, we attribute
the observed pattern to the symmetry breaking produced by the ligand where the
chain is attached, plus carbon pi-bonding alternation.Comment: 2 pages 1 fig, PRB commen
Jahn-Teller distortions and excitation energies in C60(n+)
Based on previously computed parameters for the electron-phonon couplings and
the Coulomb exchange, we compute and classify the static Jahn-Teller
distortions, i.e. the minima of the lowest adiabatic potential energy surface,
of C60(n+), for all values of charge 1 <= n <= 9 and spin. We compute the
intra-band electronic excitation energies in the different optimal geometries
in the sudden approximation, and find a spread of the electronic states of
roughly 1 eV. We also obtain the leading vibronic quantum corrections to the
ground-state energy, equal to zero-point energy lowering due to the softening
of the phonons at the adiabatic Jahn-Teller minima: these non-adiabatic
corrections are so large that for 4 <= n <= 6 states of different spin symmetry
turn lower than the high-spin adiabatic ground state.Comment: 19 pages, proceedings of the XVI Jahn-Teller Conference - Leuven
(Be), 26/8 - 1/9 200
An optimized algebraic basis for molecular potentials
The computation of vibrational spectra of diatomic molecules through the
exact diagonalization of algebraically determined matrixes based on powers of
Morse coordinates is made substantially more efficient by choosing a properly
adapted quantum-mechanical basis, specifically tuned to the molecular
potential. A substantial improvement is achieved while still retaining the full
advantage of the simplicity and numerical light-weightedness of an algebraic
approach. In the scheme we propose, the basis is parameterized by two
quantities which can be adjusted to best suit the molecular potential through a
simple minimization procedure.Comment: 29 pages, 4 tables and 4 figures, latex. Sumbitted to J. Phys. Chem
Crystalline misfit-angle implications for solid sliding
For the contact of two finite portions of interacting rigid crystalline
surfaces, we compute the dependence of the pinning energy barrier on the misfit
angle and contact area. The resulting data are used to investigate the
distribution of static frictional thresholds for a contact of polycrystal
surfaces, as occurs at the touching points of dry or even lubricated friction.
The simplicity of the model allows us to investigate a broad contact-size and
angular range, thus obtaining the statistical properties of the energy barriers
opposing sliding for a single asperity. These statistical properties are used
as the input of a master-equation model to predict the sliding properties of
two macroscopic surfaces in contact. The model is consistent with the
well-established result that low temperature should generally favor stick-slip
motion, while at high temperature sliding should be smooth.Comment: 11 pages, including 7 figure
Expansion of a Fermi Cloud in the BCS-BEC Crossover
We study the free expansion of a dilute two-component Fermi gas with
attractive interspecies interaction in the BCS-BEC crossover. We apply a
time-dependent parameter-free density-functional theory by using two choices of
the equation of state: an analytic formula based on Monte Carlo data and the
mean-field equation of state resulting from the extended BCS equations. The
calculated axial and transverse radii and the aspect ratio of the expanding
cloud are compared to experimental data on vapors of ^6Li atoms. Remarkably,
the mean-field theory shows a better agreement with the experiments than the
theory based on the Monte Carlo equation of state. Both theories predict a
measurable dependence of the aspect ratio on expansion time and on scattering
length.Comment: 5 pages, 3 figure
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