98,757 research outputs found
Accuracy of Quantum Monte Carlo Methods for Point Defects in Solids
Quantum Monte Carlo approaches such as the diffusion Monte Carlo (DMC) method
are among the most accurate many-body methods for extended systems. Their
scaling makes them well suited for defect calculations in solids. We review the
various approximations needed for DMC calculations of solids and the results of
previous DMC calculations for point defects in solids. Finally, we present
estimates of how approximations affect the accuracy of calculations for
self-interstitial formation energies in silicon and predict DMC values of
4.4(1), 5.1(1) and 4.7(1) eV for the X, T and H interstitial defects,
respectively, in a 16(+1)-atom supercell
Pair-Hopping Mechanism for Layered Superconductors
We propose a possible charge fluctuation effect expected in layered
superconducting materials. In the multireference density functional theory,
relevant fluctuation channels for the Josephson coupling between
superconducting layers include the interlayer pair hopping derived from the
Coulomb repulsion. When interlayer single-electron tunneling processes are
irrelevant in the Kohn-Sham electronic band structure calculation, the two-body
effective interactions stabilize a superconducting phase. This state is also
regarded as a valence-bond solid in a bulk electronic state. The hidden order
parameters coexist with the superconducting order parameter when the charging
effect of a layer is comparable to the pair hopping. Relevant materials
structures favorable for the pair-hopping mechanism are discussed.Comment: 24 pages, 2 figures, to be published in J. Phys. Soc. Jpn. (2009
Investigation of the transverse beam dynamics in the thermal wave model with a functional method
We investigated the transverse beam dynamics in a thermal wave model by using
a functional method. It can describe the beam optical elements separately with
a kernel for a component. The method can be applied to general quadrupole
magnets beyond a thin lens approximation as well as drift spaces. We found that
the model can successfully describe the PARMILA simulation result through an
FODO lattice structure for the Gaussian input beam without space charge
effects.Comment: 12 pages, 6 figure
Efficient Simulation of Quantum Systems by Quantum Computers
We show that the time evolution of the wave function of a quantum mechanical
many particle system can be implemented very efficiently on a quantum computer.
The computational cost of such a simulation is comparable to the cost of a
conventional simulation of the corresponding classical system. We then sketch
how results of interest, like the energy spectrum of a system, can be obtained.
We also indicate that ultimately the simulation of quantum field theory might
be possible on large quantum computers.
We want to demonstrate that in principle various interesting things can be
done. Actual applications will have to be worked out in detail also depending
on what kind of quantum computer may be available one day...Comment: 8 pages, latex, submitted to Phys. Rev. A, revised version has about
double length of original and contains new ideas, e.g. how to obtain the
spectrum of a quantum syste
Reconstruction of annular bi-layered media in cylindrical waveguide section
A radial transverse resonance model for two cylindrical concentric layers
with different complex dielectric constants is presented. An inverse problem
with four unknowns - 3 physical material parameters and one dimensional
dielectric layer thickness parameter- is solved by employing TE110 and TE210
modes with different radial field distribution. First a Newton-Raphson
algorithm is used to solve a least square problem with a Lorentzian function
(as resonance model and "measured" data generator). Then found resonance
frequencies and quality factors are used in a second inverse Newton-Raphson
algorithm that solves four transverse resonance equations in order to get four
unknown parameters. The use of TE110 and TE210 models offers one dimensional
radial tomographic capability. An open ended coax quarter-wave resonator is
added to the sensor topology, and the effect on the convergence is
investigated
A Radial-Dependent Dispersive Finite-Difference Time-Domain Method for the Evaluation of Electromagnetic Cloaks
A radial-dependent dispersive finite-difference time-domain (FDTD) method is
proposed to simulate electromagnetic cloaking devices. The Drude dispersion
model is applied to model the electromagnetic characteristics of the cloaking
medium. Both lossless and lossy cloaking materials are examined and their
operating bandwidth is also investigated. It is demonstrated that the perfect
"invisibility" from electromagnetic cloaks is only available for lossless
metamaterials and within an extremely narrow frequency band.Comment: 18 pages, 10 figure
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