884 research outputs found
Interaction energy functional for lattice density functional theory: Applications to one-, two- and three-dimensional Hubbard models
The Hubbard model is investigated in the framework of lattice density
functional theory (LDFT). The single-particle density matrix with
respect the lattice sites is considered as the basic variable of the many-body
problem. A new approximation to the interaction-energy functional
is proposed which is based on its scaling properties and which recovers exactly
the limit of strong electron correlations at half-band filling. In this way, a
more accurate description of is obtained throughout the domain of
representability of , including the crossover from weak to strong
correlations. As examples of applications results are given for the
ground-state energy, charge-excitation gap, and charge susceptibility of the
Hubbard model in one-, two-, and three-dimensional lattices. The performance of
the method is demonstrated by comparison with available exact solutions, with
numerical calculations, and with LDFT using a simpler dimer ansatz for .
Goals and limitations of the different approximations are discussed.Comment: 25 pages and 8 figures, submitted to Phys. Rev.
Density-Matrix functional theory of strongly-correlated lattice fermions
A density functional theory (DFT) of lattice fermion models is presented,
which uses the single-particle density matrix gamma_{ij} as basic variable. A
simple, explicit approximation to the interaction-energy functional W[gamma] of
the Hubbard model is derived from exact dimer results, scaling properties of
W[gamma] and known limits. Systematic tests on the one-dimensional chain show a
remarkable agreement with theBethe-Ansatz exact solution for all interaction
regimes and band fillings. New results are obtained for the ground-state
energyand charge-excitation gap in two dimensions. A successful description of
strong electron correlations within DFT is achieved.Comment: 15 pages, 6 figures Submitted to PR
Genetic algorithm optimization of entanglement
We present an application of a genetic algorithmic computational method to
the optimization of the concurrence measure of entanglement for the cases of
one dimensional chains, as well as square and triangular lattices in a simple
tight-binding approach in which the hopping of electrons is much stronger than
the phonon dissipationComment: 26 pages with 13 figures, based on Chapter 3 of the Master thesis of
the first author defended at IPICyT, San Luis Potosi, Mx, on 22nd of February
2006, similar to the published version [Fig. 5 left out but contains the
Appendix figure
Power Series Solution for Solving Nonlinear Burgers-Type Equations
Power series solution method has been traditionally used to solve ordinary and partial linear differential equations. However, despite their usefulness the application of this method has been limited to this particular kind of equations. In this work we use the method of power series to solve nonlinear partial differential equations. The method is applied to solve three versions of nonlinear time-dependent Burgers-type differential equations in order to demonstrate its scope and applicability
Density-matrix functional theory of the Hubbard model: An exact numerical study
A density functional theory for many-body lattice models is considered in
which the single-particle density matrix is the basic variable. Eigenvalue
equations are derived for solving Levy's constrained search of the interaction
energy functional W, which is expressed as the sum of Hartree-Fock energy and
the correlation energy E_C. Exact results are obtained for E_C of the Hubbard
model on various periodic lattices. The functional dependence of E_C is
analyzed by varying the number of sites, band filling and lattice structure.
The infinite one-dimensional chain and one-, two-, or three-dimensional finite
clusters with periodic boundary conditions are considered. The properties of
E_C are discussed in the limits of weak and strong electronic correlations, as
well as in the crossover region. Using an appropriate scaling we observe a
pseudo-universal behavior which suggests that the correlation energy of
extended systems could be obtained quite accurately from finite cluster
calculations. Finally, the behavior of E_C for repulsive (U>0) and attractive
(U<0) interactions are contrasted.Comment: Phys. Rev. B (1999), in pres
Morphology and thermal stability of alf3 on Cu(100) thin films
Se estudió el crecimiento de películas epitaxiales ultra-delgadas de fluoruro de aluminio en Cu (100) mediante una combinación de técnicas experimentales de física de superficies. La deposición a temperatura ambiente resulta en la decoración de escalones seguida por la formación de islas dendríticas bidimensionales que coalescen para formar películas porosas. Las películas ultra-delgadas (de hasta dos monocapas de espesor) resultan morfológicamente inestables al calentar; parte de la película deja de mojar la superficie del sustrato a alrededor de 430 K con la formación de islas tridimensionales y dejando expuesta un área extensa de la superficie de Cu. En cambio, películas de varios nanómetros de espesor son estables hasta temperaturas cercanas a los 730 K cuando ocurre la desorción molecular. El efecto de la irradiación electrónica también ha sido caracterizado mediante diferentes técnicas espectroscópicas; encontrando que incluso dosis de irradiación reducidas de electrones pueden producir una descomposición significativa del fluoruro de aluminio, resultando en la liberación de moléculas de flúor y la formación de aluminio metálico. Estas características hacen del fluoruro de aluminio un material interesante para aplicaciones en espintrónica.Fil: Ruano Sandoval, Gonzalo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Moreno López, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Passeggi, Mario Cesar Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Vidal, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Ferron, Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Niño, M. A.. Universidad Autónoma de Madrid; EspañaFil: Miranda, R.. Universidad Autónoma de Madrid; EspañaFil: de Miguel, J. J.. Universidad Autónoma de Madrid; Españ
Designing lattice structures with maximal nearest-neighbor entanglement
In this work, we study the numerical optimization of nearest-neighbor
concurrence of bipartite one and two dimensional lattices, as well as non
bipartite two dimensional lattices. These systems are described in the
framework of a tight-binding Hamiltonian while the optimization of concurrence
was performed using genetic algorithms. Our results show that the concurrence
of the optimized lattice structures is considerably higher than that of non
optimized systems. In the case of one dimensional chains the concurrence is
maximized when the system begins to dimerize, i.e. it undergoes a structural
phase transition (Peierls distortion). This result is consistent with the idea
that entanglement is maximal or shows a singularity near quantum phase
transitions and that quantum entanglement cannot be freely shared between many
objects (monogamy property). Moreover, the optimization of concurrence in
two-dimensional bipartite and non bipartite lattices is achieved when the
structures break into smaller subsystems, which are arranged in geometrically
distinguishable configurations. This behavior is again related to the monogamy
property.Comment: 18 pages, 10 figure
Field analysis of solar PV-based collective systems for rural electrification.
This article analyses the long-term performance of collective off-grid photovoltaic (PV) systems in rural areas. The use of collective PV systems for the electrification of small medium-size villages in developing countries has increased in the recent years. They are basically set up as stand-alone installations (diesel hybrid or pure PV) with no connection with other electrical grids. Their particular conditions (isolated) and usual installation places (far from commercial/industrial centers) require an autonomous and reliable technology. Different but related factors affect their performance and the energy supply; some of them are strictly technical but others depend on external issues like the solar energy resource and users’ energy and power consumption. The work presented is based on field operation of twelve collective PV installations supplying the electricity to off-grid villages located in the province of Jujuy, Argentina. Five of them have PV generators as unique power source while other seven include the support of diesel groups. Load demand evolution, energy productivity and fuel consumption are analyzed. Besides, energy generation strategies (PV/diesel) are also discussed
All-particle cosmic ray energy spectrum measured by the HAWC experiment from 10 to 500 TeV
We report on the measurement of the all-particle cosmic ray energy spectrum
with the High Altitude Water Cherenkov (HAWC) Observatory in the energy range
10 to 500 TeV. HAWC is a ground based air-shower array deployed on the slopes
of Volcan Sierra Negra in the state of Puebla, Mexico, and is sensitive to
gamma rays and cosmic rays at TeV energies. The data used in this work were
taken from 234 days between June 2016 to February 2017. The primary cosmic-ray
energy is determined with a maximum likelihood approach using the particle
density as a function of distance to the shower core. Introducing quality cuts
to isolate events with shower cores landing on the array, the reconstructed
energy distribution is unfolded iteratively. The measured all-particle spectrum
is consistent with a broken power law with an index of prior to
a break at ) TeV, followed by an index of . The
spectrum also respresents a single measurement that spans the energy range
between direct detection and ground based experiments. As a verification of the
detector response, the energy scale and angular resolution are validated by
observation of the cosmic ray Moon shadow's dependence on energy.Comment: 16 pages, 11 figures, 4 tables, submission to Physical Review
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