79 research outputs found
Rules for Minimal Atomic Multipole Expansion of Molecular Fields
A non-empirical minimal atomic multipole expansion (MAME) defines atomic
charges or higher multipoles that reproduce electrostatic potential outside
molecules. MAME eliminates problems associated with redundancy and with
statistical sampling, and produces atomic multipoles in line with chemical
intuition.Comment: 3.5 pages, 3 color PS figures embedde
Anomalous magnetophotoluminescence as a result of level repulsion in arrays of quantum dots
Selectively excited photoluminescence (SPL) of an array of self-organized
InGaAs quantum dots has been measured in a magnetic field up to
11T. Anomalous magnetic field sensitivity of the SPL spectra has been observed
under conditions for which the regular photoluminescence spectra is insensitive
to the magnetic field due to large inhomogeneous broadening. The anomalous
sensitivity is interpreted in terms of the repulsion of excited levels of the
dots in a random potential. A theory presented to describe this phenomena is in
excellent agreement with the experimental data. The data estimated the
correlation in the positions of excited levels of the dots to be 94%. The
magnetic field dependence allows the determination of the reduced cyclotron
effective mass in a dot. For our sample we have obtained
.Comment: 12 revtex preprint pages + 4 ps figures, uuencode
Analytic Coulomb matrix elements in the lowest Landau level in disk geometry
Using Darling's theorem on products of generalized hypergeometric series an
analytic expression is obtained for the Coulomb matrix elements in the lowest
Landau level in the representation of angular momentum. The result is important
in the studies of Fractional Quantum Hall effect (FQHE) in disk geometry.
Matrix elements are expressed as simple finite sums of positive terms,
eliminating the need to approximate these quantities with slowly-convergent
series. As a by-product, an analytic representation for certain integals of
products of Laguerre polynomials is obtained.Comment: Accepted to J. Math. Phys.; 3 pages revtex, no figure
Optical properties of arrays of quantum dots with internal disorder
Optical properties of large arrays of isolated quantum dots are discussed in
order to interpret the existent photoluminescence data. The presented theory
explains the large observed shift between the lowest emission and absorption
energies as the average distance between the ground and first excited states of
the dots. The lineshape of the spectra is calculated for the case when the
fluctuations of the energy levels in quantum dots are due to the alloy
composition fluctuations. The calculated lineshape is in good agreement with
the experimental data. The influence of fluctuations of the shape of quantum
dots on the photoluminescence spectra is also discussed.Comment: 7 pages (twocolumn) LATEX, 6 Postscript figure
Polarization forces in water deduced from single molecule data
Intermolecular polarization interactions in water are determined using a
minimal atomic multipole model constructed with distributed polarizabilities.
Hydrogen bonding and other properties of water-water interactions are
reproduced to fine detail by only three multipoles , , and
and two polarizabilities and , which
characterize a single water molecule and are deduced from single molecule data.Comment: 4 revtex pages, 3 embedded color PS figure
Reconstruction of Fractional Quantum Hall Edges
We study the interplay of interaction, confining potential and effects of
finite temperature at the edge of a quantum Hall liquid. Our exact
diagonalization calculation indicates that edge reconstruction occurs in the
fractional quantum Hall regime for a variety of confining potential, including
ones that correspond to a "sharp" edge. Our finite temperature Hartree-Fock
calculation for integer quantum Hall edges indicates that reconstruction is
suppressed above certain temperature. We discuss the implication of our results
on recent edge tunneling and microwave absorption experiments.Comment: Revised version. 5 papges RevTex with 5 eps figures embedded in the
tex
Supramolecular interactions in clusters of polar and polarizable molecules
We present a model for molecular materials made up of polar and polarizable
molecular units. A simple two state model is adopted for each molecular site
and only classical intermolecular interactions are accounted for, neglecting
any intermolecular overlap. The complex and interesting physics driven by
interactions among polar and polarizable molecules becomes fairly transparent
in the adopted model. Collective effects are recognized in the large variation
of the molecular polarity with supramolecular interactions, and cooperative
behavior shows up with the appearance, in attractive lattices, of discontinuous
charge crossovers. The mean-field approximation proves fairly accurate in the
description of the gs properties of MM, including static linear and non-linear
optical susceptibilities, apart from the region in the close proximity of the
discontinuous charge crossover. Sizeable deviations from the excitonic
description are recognized both in the excitation spectrum and in linear and
non-linear optical responses. New and interesting phenomena are recognized near
the discontinuous charge crossover for non-centrosymmetric clusters, where the
primary photoexcitation event corresponds to a multielectron transfer.Comment: 14 pages, including 11 figure
Density Modulations and Addition Spectra of Interacting Electrons in Disordered Quantum Dots
We analyse the ground state of spinless fermions on a lattice in a weakly
disordered potential, interacting via a nearest neighbour interaction, by
applying the self-consistent Hartree-Fock approximation. We find that charge
density modulations emerge progressively when r_s >1, even away from
half-filling, with only short-range density correlations. Classical geometry
dependent "magic numbers" can show up in the addition spectrum which are
remarkably robust against quantum fluctuations and disorder averaging.Comment: 4 pages, 3 eps figure
Strong polarization-induced reduction of addition energies in single-molecule nanojunctions
We address polarization-induced renormalization of molecular levels in
solid-state based single-molecule transistors and focus on an organic conjugate
molecule where a surprisingly large reduction of the addition energy has been
observed. We have developed a scheme that combines a self-consistent solution
of a quantum chemical calculation with a realistic description of the screening
environment. Our results indeed show a large reduction, and we explain this to
be a consequence of both (a) a reduction of the electrostatic molecular
charging energy and (b) polarization induced level shifts of the HOMO and LUMO
levels. Finally, we calculate the charge stability diagram and explain at a
qualitative level general features observed experimentally.Comment: 9 pages, 5 figure
Quantum dots in high magnetic fields: Rotating-Wigner-molecule versus composite-fermion approach
Exact diagonalization results are reported for the lowest rotational band of
N=6 electrons in strong magnetic fields in the range of high angular momenta 70
<= L <= 140 (covering the corresponding range of fractional filling factors 1/5
>= nu >= 1/9). A detailed comparison of energetic, spectral, and transport
properties (specifically, magic angular momenta, radial electron densities,
occupation number distributions, overlaps and total energies, and exponents of
current-voltage power law) shows that the recently discovered
rotating-electron-molecule wave functions [Phys. Rev. B 66, 115315 (2002)]
provide a superior description compared to the
composite-fermion/Jastrow-Laughlin ones.Comment: Extensive clarifications were added (see new footnotes) regarding the
difference between the rotating Wigner molecule and the bulk Wigner crystal;
also regarding the influence of an external confining potential. 12 pages.
Revtex4 with 6 EPS figures and 5 tables . For related papers, see
http://www.prism.gatech.edu/~ph274c
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