49,866 research outputs found
Ab-initio self-consistent Gorkov-Green's function calculations of semi-magic nuclei - II. Numerical implementation at second order with a two-nucleon interaction
The newly developed Gorkov-Green's function approach represents a promising
path to the ab initio description of medium-mass open-shell nuclei. We discuss
the implementation of the method at second order with a two-body interaction,
with particular attention to the numerical solution of Gorkov's equation.
Different sources of theoretical error and degrees of self-consistency are
investigated. We show that Krylov projection techniques with a multi-pivot
Lanczos algorithm efficiently handle the growth of poles in the one-body
Green's function when Gorkov's equation is solved self-consistently. The end
result is a tractable, accurate and gently scaling ab initio scheme applicable
to full isotopic chains in the medium-mass region.Comment: 17 pages, 13 figure
Numerical renormalization group study of random transverse Ising models in one and two space dimensions
The quantum critical behavior and the Griffiths-McCoy singularities of random
quantum Ising ferromagnets are studied by applying a numerical implementation
of the Ma-Dasgupta-Hu renormalization group scheme. We check the procedure for
the analytically tractable one-dimensional case and apply our code to the
quasi-one-dimensional double chain. For the latter we obtain identical critical
exponents as for the simple chain implying the same universality class. Then we
apply the method to the two-dimensional case for which we get estimates for the
exponents that are compatible with a recent study in the same spirit.Comment: 10 pages LaTeX, eps-figures and PTP-macros included. Proceedings of
the ICCP5, Kanazawa (Japan), 199
Numerical analysis of the dissipative two-state system with the density-matrix Hilbert-space-reduction algorithm
Ground state of the dissipative two-state system is investigated by means of
the Lanczos diagonalization method. We adopted the Hilbert-space-reduction
scheme proposed by Zhang, Jeckelmann and White so as to reduce the overwhelming
reservoir Hilbert space to being tractable in computers. Both the
implementation of the algorithm and the precision applied for the present
system are reported in detail. We evaluate the dynamical susceptibility
(resolvent) with the continued-fraction-expansion formula. Through analysing
the resolvent over a frequency range, whose range is often called `interesting'
frequency, we obtain the damping rate and the oscillation frequency. Our
results agree with those of a recent quantum Monte-Carlo study, which concludes
that the critical dissipation from oscillatory to over-damped behavior
decreases as the tunneling amplitude is strengthened
Time-dependent quantum transport: A practical scheme using density functional theory
We present a computationally tractable scheme of time-dependent transport
phenomena within open-boundary time-dependent density-functional-theory. Within
this approach all the response properties of a system are determined from the
time-propagation of the set of ``occupied'' Kohn-Sham orbitals under the
influence of the external bias. This central idea is combined with an
open-boundary description of the geometry of the system that is divided into
three regions: left/right leads and the device region (``real simulation
region''). We have derived a general scheme to extract the set of initial
states in the device region that will be propagated in time with proper
transparent boundary-condition at the device/lead interface. This is possible
due to a new modified Crank-Nicholson algorithm that allows an efficient
time-propagation of open quantum systems. We illustrate the method in
one-dimensional model systems as a first step towards a full first-principles
implementation. In particular we show how a stationary current develops in the
system independent of the transient-current history upon application of the
bias. The present work is ideally suited to study ac transport and
photon-induced charge-injection. Although the implementation has been done
assuming clamped ions, we discuss how it can be extended to include dissipation
due to electron-phonon coupling through the combined simulation of the
electron-ion dynamics as well as electron-electron correlations.Comment: 14 pages, 9 figures, one of which consist of two separate file
A Tractable Forward-Backward CPHD Smoother
To circumvent the intractability of the usual Cardinalized Probability Hypothesis Density (CPHD) smoother, we present an approximate scheme where the population of targets born until and after the starting time of the smoothing are estimated separately and where smoothing is only applied to the estimate of the former population. The approach is illustrated through the implementation of a tractable approximation of the usual CPHD smoother
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