1,335 research outputs found
Carleman estimates and absence of embedded eigenvalues
Let L be a Schroedinger operator with potential W in L^{(n+1)/2}. We prove
that there is no embedded eigenvalue. The main tool is an Lp Carleman type
estimate, which builds on delicate dispersive estimates established in a
previous paper. The arguments extend to variable coefficient operators with
long range potentials and with gradient potentials.Comment: 26 page
Efficient Algorithm for Asymptotics-Based Configuration-Interaction Methods and Electronic Structure of Transition Metal Atoms
Asymptotics-based configuration-interaction (CI) methods [G. Friesecke and B.
D. Goddard, Multiscale Model. Simul. 7, 1876 (2009)] are a class of CI methods
for atoms which reproduce, at fixed finite subspace dimension, the exact
Schr\"odinger eigenstates in the limit of fixed electron number and large
nuclear charge. Here we develop, implement, and apply to 3d transition metal
atoms an efficient and accurate algorithm for asymptotics-based CI.
Efficiency gains come from exact (symbolic) decomposition of the CI space
into irreducible symmetry subspaces at essentially linear computational cost in
the number of radial subshells with fixed angular momentum, use of reduced
density matrices in order to avoid having to store wavefunctions, and use of
Slater-type orbitals (STO's). The required Coulomb integrals for STO's are
evaluated in closed form, with the help of Hankel matrices, Fourier analysis,
and residue calculus.
Applications to 3d transition metal atoms are in good agreement with
experimental data. In particular we reproduce the anomalous magnetic moment and
orbital filling of Chromium in the otherwise regular series Ca, Sc, Ti, V, Cr.Comment: 14 pages, 1 figur
Exchange-assisted tunneling in the classical limit
The exchange interaction and correlations may produce a power-law decay
instead of the usual exponential decrease of the wave function under potential
barrier. The exchange-assisted tunneling vanishes in the classical limit,
however, the dependence on the Planck constant h is different from that for a
conventional single-particle tunneling
Magnetism in purple bronze LiMoO
Muon spin relaxation measurements around the 25 K metal-insulator transition
in LiMoO elucidate a profound role of disorder as a possible
mechanism for this transition. The relaxation rate and the muon Knight
shift are incompatible with the transition to a SDW state and thus exclude it.Comment: pages 2, fig 2, The conf. on strongly correlated electron systems,
SCES 2004, German
Implementation of screened hybrid functionals based on the Yukawa potential within the LAPW basis set
The implementation of screened hybrid functionals into the WIEN2k code, which
is based on the LAPW basis set, is reported. The Hartree-Fock exchange energy
and potential are screened by means of the Yukawa potential as proposed by
Bylander and Kleinman [Phys. Rev. B 41, 7868 (1990)] for the calculation of the
electronic structure of solids with the screened-exchange local density
approximation. Details of the formalism, which is based on the method of
Massidda, Posternak, and Baldereschi [Phys. Rev. B 48, 5058 (1993)] for the
unscreened Hartree-Fock exchange are given. The results for the
transition-energy and structural properties of several test cases are
presented. Results of calculations of the Cu electric-field gradient in Cu2O
are also presented, and it is shown that the hybrid functionals are much more
accurate than the standard local-density or generalized gradient
approximations
Spectroscopy and dissociative recombination of the lowest rotational states of H3+
The dissociative recombination of the lowest rotational states of H3+ has
been investigated at the storage ring TSR using a cryogenic 22-pole
radiofrequency ion trap as injector. The H3+ was cooled with buffer gas at ~15
K to the lowest rotational levels, (J,G)=(1,0) and (1,1), which belong to the
ortho and para proton-spin symmetry, respectively. The rate coefficients and
dissociation dynamics of H3+(J,G) populations produced with normal- and para-H2
were measured and compared to the rate and dynamics of a hot H3+ beam from a
Penning source. The production of cold H3+ rotational populations was
separately studied by rovibrational laser spectroscopy using chemical probing
with argon around 55 K. First results indicate a ~20% relative increase of the
para contribution when using para-H2 as parent gas. The H3+ rate coefficient
observed for the para-H2 source gas, however, is quite similar to the H3+ rate
for the normal-H2 source gas. The recombination dynamics confirm that for both
source gases, only small populations of rotationally excited levels are
present. The distribution of 3-body fragmentation geometries displays a broad
part of various triangular shapes with an enhancement of ~12% for events with
symmetric near-linear configurations. No large dependences on internal state or
collision energy are found.Comment: 10 pages, 9 figures, to be published in Journal of Physics:
Conference Proceeding
Anisotropic fragmentation in low-energy dissociative recombination
On a dense energy grid reaching up to 75 meV electron collision energy the
fragmentation angle and the kinetic energy release of neutral dissociative
recombination fragments have been studied in a twin merged beam experiment. The
anisotropy described by Legendre polynomials and the extracted rotational state
contributions were found to vary on a likewise narrow energy scale as the
rotationally averaged rate coefficient. For the first time angular dependences
higher than 2 order could be deduced. Moreover, a slight anisotropy at
zero collision energy was observed which is caused by the flattened velocity
distribution of the electron beam.Comment: 8 pages, 4 figures; The Article will be published in the proceedings
of DR 2007, a symposium on Dissociative Recombination held in Ameland, The
Netherlands (18.-23. July 2008); Reference 19 has been published meanwhile in
S. Novotny, PRL 100, 193201 (2008
Positronic lithium, an electronically stable Li-e ground state
Calculations of the positron-Li system were performed using the Stochastic
Variational Method and yielded a minimum energy of -7.53208 Hartree for the L=0
ground state. Unlike previous calculations of this system, the system was found
to be stable against dissociation into the Ps + Li channel with a binding
energy of 0.00217 Hartree and is therefore electronically stable. This is the
first instance of a rigorous calculation predicting that it is possible to
combine a positron with a neutral atom and form an electronically stable bound
state.Comment: 11 pages, 2 tables. To be published in Phys.Rev.Let
On the secondly quantized theory of many-electron atom
Traditional theory of many-electron atoms and ions is based on the
coefficients of fractional parentage and matrix elements of tensorial
operators, composed of unit tensors. Then the calculation of spin-angular
coefficients of radial integrals appearing in the expressions of matrix
elements of arbitrary physical operators of atomic quantities has two main
disadvantages: (i) The numerical codes for the calculation of spin-angular
coefficients are usually very time-consuming; (ii) f-shells are often omitted
from programs for matrix element calculation since the tables for their
coefficients of fractional parentage are very extensive. The authors suppose
that a series of difficulties persisting in the traditional approach to the
calculation of spin-angular parts of matrix elements could be avoided by using
this secondly quantized methodology, based on angular momentum theory, on the
concept of the irreducible tensorial sets, on a generalized graphical method,
on quasispin and on the reduced coefficients of fractional parentage
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