10,959 research outputs found
Square root kalman filter with contaminated observations.
The algorithm of square root Kalman filtering for the case of contaminated observations is described in the paper. This algorithm is suitable for the parallel computer implementation allowing to treat dynamic linear systems with large number of state variables in a robust recursive way.Square root Kalman filter; Robust; Parallel algorithm;
Charge-transfer in time-dependent density-functional theory via spin-symmetry-breaking
Long-range charge-transfer excitations pose a major challenge for
time-dependent density functional approximations. We show that
spin-symmetry-breaking offers a simple solution for molecules composed of
open-shell fragments, yielding accurate excitations at large separations when
the acceptor effectively contains one active electron. Unrestricted
exact-exchange and self-interaction-corrected functionals are performed on
one-dimensional models and the real LiH molecule within the pseudopotential
approximation to demonstrate our results.Comment: 5 pages, 4 figure
Self-consistent DFT+U method for real-space time-dependent density functional theory calculations
We implemented various DFT+U schemes, including the ACBN0 self-consistent
density-functional version of the DFT+U method [Phys. Rev. X 5, 011006 (2015)]
within the massively parallel real-space time-dependent density functional
theory (TDDFT) code Octopus. We further extended the method to the case of the
calculation of response functions with real-time TDDFT+U and to the description
of non-collinear spin systems. The implementation is tested by investigating
the ground-state and optical properties of various transition metal oxides,
bulk topological insulators, and molecules. Our results are found to be in good
agreement with previously published results for both the electronic band
structure and structural properties. The self consistent calculated values of U
and J are also in good agreement with the values commonly used in the
literature. We found that the time-dependent extension of the self-consistent
DFT+U method yields improved optical properties when compared to the empirical
TDDFT+U scheme. This work thus opens a different theoretical framework to
address the non equilibrium properties of correlated systems
Optical observations of very low ionization HII regions in the large Magellanic cloud
Several very low ionization isolated HII regions were detected on a prism-objective plate of the Large Magellanic Cloud. Most of the objects show a very weak (OIII) lambda 5007 emission line and, on the other hand the (OII) lambda 6584 doublets are very intense. This kind of objects seem to be ideal in order to determine accurate N and O abundance, avoiding the use of large ionization correction factors in the N abundance determination. Spectrophotometric observations of these regions were carried out with the 4 m telescope and the 2-D Frutti spectrograph at Cerro Tololo, and with the 1.52 m and the Image Dissector Scanner (IDS) at La Silla, ESO. The wavelength range lambda lambda 3700 to 7000 A was covered. Calibrated fluxes of the emission lines detected were measured, and from these data preliminary results of physical conditions of the gas as well as some ionic abundances were derived. Comparisons of the observations with ionization structure models show that the effective temperatures of the ionizing stars are less than 35,000 K. Possible abundances gradients across the large megallanic cloud are discussed
Universal Dynamical Steps in the Exact Time-Dependent Exchange-Correlation Potential
We show that the exact exchange-correlation potential of time-dependent
density-functional theory displays dynamical step structures that have a
spatially non-local and time non-local dependence on the density. Using
one-dimensional two-electron model systems, we illustrate these steps for a
range of non-equilibrium dynamical situations relevant for modeling of
photo-chemical/physical processes: field-free evolution of a non-stationary
state, resonant local excitation, resonant complete charge-transfer, and
evolution under an arbitrary field. Lack of these steps in usual approximations
yield inaccurate dynamics, for example predicting faster dynamics and
incomplete charge transfer
-AlN-Mg(OH) vdW Bilayer Heterostructure: Tuning the excitonic characteristics
Motivated by recent studies that reported the successful synthesis of
monolayer Mg(OH) [Suslu \textit{et al.}, Sci. Rep. \textbf{6}, 20525
(2016)] and hexagonal (\textit{h}-)AlN [Tsipas \textit{et al}., Appl. Phys.
Lett. \textbf{103}, 251605 (2013)], we investigate structural, electronic, and
optical properties of vertically stacked -AlN and Mg(OH), through
\textit{ab initio} density-functional theory (DFT), many-body quasi-particle
calculations within the GW approximation, and the Bethe-Salpeter equation
(BSE). It is obtained that the bilayer heterostructure prefers the
stacking having direct band gap at the with Type-II band
alignment in which the valance band maximum and conduction band minimum
originate from different layer. Regarding the optical properties, the imaginary
part of the dielectric function of the individual layers and hetero-bilayer are
investigated. The hetero-bilayer possesses excitonic peaks which appear only
after the construction of the hetero-bilayer. The lowest three exciton peaks
are detailedly analyzed by means of band decomposed charge density and the
oscillator strength. Furthermore, the wave function calculation shows that the
first peak of the hetero-bilayer originates from spatially indirect exciton
where the electron and hole localized at -AlN and Mg(OH),
respectively, which is important for the light harvesting applications.Comment: Accepted by Physical Review
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