25 research outputs found
An analytic expression for the electronic correlation term of the kinetic functional
We propose an analytic formula for the non-local Fisher information
functional, or electronic kinetic correlation term, appearing in the expression
of the kinetic density functional. Such an explicit formula is constructed on
the basis of well-founded physical arguments and a rigorous mathematical
prescription
On the upper bound of the electronic kinetic energy in terms of density functionals
We propose a simple density functional expression for the upper bound of the
kinetic energy for electronic systems. Such a functional is valid in the limit
of slowly varying density, its validity outside this regime is discussed by
making a comparison with upper bounds obtained in previous work. The advantages
of the functional proposed for applications to realistic systems is briefly
discussed.Comment: 10 pages, no figure
Methodology for developing an advanced communications system for the Deaf in a new domain
A methodology for developing an advanced communications system for the Deaf in a new domain is presented in this paper. This methodology is a user-centred design approach consisting of four main steps: requirement analysis, parallel corpus generation, technology adaptation to the new domain, and finally, system evaluation. During the requirement analysis, both the user and technical requirements are evaluated and defined. For generating the parallel corpus, it is necessary to collect Spanish sentences in the new domain and translate them into LSE (Lengua de Signos Española: Spanish Sign Language). LSE is represented by glosses and using video recordings. This corpus is used for training the two main modules of the advanced communications system to the new domain: the spoken Spanish into the LSE translation module and the Spanish generation from the LSE module. The main aspects to be generated are the vocabularies for both languages (Spanish words and signs), and the knowledge for translating in both directions. Finally, the field evaluation is carried out with deaf people using the advanced communications system to interact with hearing people in several scenarios. In this evaluation, the paper proposes several objective and subjective measurements for evaluating the performance. In this paper, the new considered domain is about dialogues in a hotel reception. Using this methodology, the system was developed in several months, obtaining very good performance: good translation rates (10% Sign Error Rate) with small processing times, allowing face-to-face dialogues
Constraint-based, Single-point Approximate Kinetic Energy Functionals
We present a substantial extension of our constraint-based approach for
development of orbital-free (OF) kinetic-energy (KE) density functionals
intended for the calculation of quantum-mechanical forces in multi-scale
molecular dynamics simulations. Suitability for realistic system simulations
requires that the OF-KE functional yield accurate forces on the nuclei yet be
relatively simple. We therefore require that the functionals be based on DFT
constraints, local, dependent upon a small number of parameters fitted to a
training set of limited size, and applicable beyond the scope of the training
set. Our previous "modified conjoint" generalized-gradient-type functionals
were constrained to producing a positive-definite Pauli potential. Though
distinctly better than several published GGA-type functionals in that they gave
semi-quantitative agreement with Born-Oppenheimer forces from full Kohn-Sham
results, those modified conjoint functionals suffer from unphysical
singularities at the nuclei. Here we show how to remove such singularities by
introducing higher-order density derivatives. We give a simple illustration of
such a functional used for the dissociation energy as a function of bond length
for selected molecules.Comment: 16 pages, 9 figures, 2 tables, submitted to Phys. Rev.
Laplacian-level density functionals for the kinetic energy density and exchange-correlation energy
We construct a Laplacian-level meta-generalized gradient approximation
(meta-GGA) for the non-interacting (Kohn-Sham orbital) positive kinetic energy
density of an electronic ground state of density . This meta-GGA is
designed to recover the fourth-order gradient expansion in the
appropiate slowly-varying limit and the von Weizs\"{a}cker expression
in the rapidly-varying limit. It is constrained to
satisfy the rigorous lower bound .
Our meta-GGA is typically a strong improvement over the gradient expansion of
for atoms, spherical jellium clusters, jellium surfaces, the Airy gas,
Hooke's atom, one-electron Gaussian density, quasi-two dimensional electron
gas, and nonuniformly-scaled hydrogen atom. We also construct a Laplacian-level
meta-GGA for exchange and correlation by employing our approximate in
the Tao, Perdew, Staroverov and Scuseria (TPSS) meta-GGA density functional.
The Laplacian-level TPSS gives almost the same exchange-correlation enhancement
factors and energies as the full TPSS, suggesting that and
carry about the same information beyond that carried by and . Our
kinetic energy density integrates to an orbital-free kinetic energy functional
that is about as accurate as the fourth-order gradient expansion for many real
densities (with noticeable improvement in molecular atomization energies), but
considerably more accurate for rapidly-varying ones.Comment: 9 pages, 16 figure
Separation of the Exchange-Correlation Potential into Exchange plus Correlation: an Optimized Effective Potential Approach
Most approximate exchange-correlation functionals used within density
functional theory are constructed as the sum of two distinct contributions for
exchange and correlation. Separating the exchange component from the entire
functional is useful since, for exchange, exact relations exist under uniform
density scaling and spin scaling. In the past, accurate exchange-correlation
potentials have been generated from essentially exact densities constructed
using information from either quantum chemistry or quantum Monte Carlo
calculations but they have not been correctly decomposed into their separate
exchange and correlation components, except for two-electron systems. exchange
and correlation components (except for two-electron systems). Using a recently
proposed method, equivalent to the solution of an optimized effective potential
problem with the corresponding orbitals replaced by the exact Kohn-Sham
orbitals, we obtain the separation according to the density functional theory
definition. We compare the results for the Ne and Be atoms with those obtained
by the previously used approximate separation scheme
Design, development and field evaluation of a Spanish into sign language translation system
This paper describes the design, development and field evaluation of a machine translation system from Spanish to Spanish Sign Language (LSE: Lengua de Signos Española). The developed system focuses on helping Deaf people when they want to renew their Driver’s License. The system is made up of a speech recognizer (for decoding the spoken utterance into a word sequence), a natural language translator (for converting a word sequence into a sequence of signs belonging to the sign language), and a 3D avatar animation module (for playing back the signs). For the natural language translator, three technological approaches have been implemented and evaluated: an example-based strategy, a rule-based translation method and a statistical translator. For the final version, the implemented language translator combines all the alternatives into a hierarchical structure. This paper includes a detailed description of the field evaluation. This evaluation was carried out in the Local Traffic Office in Toledo involving real government employees and Deaf people. The evaluation includes objective measurements from the system and subjective information from questionnaires. The paper details the main problems found and a discussion on how to solve them (some of them specific for LSE)
Exact non-Born-Oppenheimer wave function for the Hooke-Calogero model of the H
The Hooke-Calogero model of the H2 molecule, a four body
system consisting of two protons and two electrons with harmonic electron-nuclear,
Coulombic electron-electron and inverse quadratic nuclear-nuclear
interactions, has been analyzed in–depth. A fully analytical
closed–form non-Born-Oppenheimer solution has been found and
based on it the properties of both electron–pair and
nuclear–pair densities have been studied. Nuclei have been found to
be strongly correlated in a way that resembles a sort of
Wigner crystallization, for moderate electron–nucleus confinement
strengths. Additionally, we have explicitly evaluated the Coulomb holes
for the electrons. Analysis of these holes reveals that
the similarity between the electron correlation effects of the model
as compared to the real Coulombic systems is remarkable