10,304 research outputs found
Combining Density Functional Theory and Density Matrix Functional Theory
We combine density-functional theory with density-matrix functional theory to
get the best of both worlds. This is achieved by range separation of the
electronic interaction which permits to rigorously combine a short-range
density functional with a long-range density-matrix functional. The short-range
density functional is approximated by the short-range version of the
Perdew-Burke-Ernzerhof functional (srPBE). The long-range density-matrix
functional is approximated by the long-range version of the Buijse-Baerends
functional (lrBB). The obtained srPBE+lrBB method accurately describes both
static and dynamic electron correlation at a computational cost similar to that
of standard density-functional approximations. This is shown for the
dissociation curves of the H, LiH, BH and HF molecules.Comment: 4 pages, 5 figure
Controllable spiking patterns in long-wavelength VCSELs for neuromorphic photonics systems
Multiple controllable spiking patterns are obtained in a 1310 nm Vertical
Cavity Surface Emitting Laser (VCSEL) in response to induced perturbations and
for two different cases of polarized optical injection, namely parallel and
orthogonal. Achievement of reproducible spiking responses in VCSELs operating
at the telecom wavelengths offers great promise for future uses of these
devices in ultrafast neuromorphic photonic systems for non-traditional
computing applications.Comment: 10 pages, 6 figures, journal submissio
On the structure of the ergosurface of Pomeransky-Senkov black rings
We study the properties of the ergosurface of the Pomeransky-Senkov black
rings, and show that it splits into an "inner"' and an "outer" region. As for
the singular set, the topology of the "outer ergosurface" depends upon the
value of parameters.Comment: 14 pages, 1 figur
Approaching Chemical Accuracy with Quantum Monte Carlo
A quantum Monte Carlo study of the atomization energies for the G2 set of
molecules is presented. Basis size dependence of diffusion Monte Carlo
atomization energies is studied with a single determinant Slater-Jastrow trial
wavefunction formed from Hartree-Fock orbitals. With the largest basis set, the
mean absolute deviation from experimental atomization energies for the G2 set
is 3.0 kcal/mol. Optimizing the orbitals within variational Monte Carlo
improves the agreement between diffusion Monte Carlo and experiment, reducing
the mean absolute deviation to 2.1 kcal/mol. Moving beyond a single determinant
Slater-Jastrow trial wavefunction, diffusion Monte Carlo with a small complete
active space Slater-Jastrow trial wavefunction results in near chemical
accuracy. In this case, the mean absolute deviation from experimental
atomization energies is 1.2 kcal/mol. It is shown from calculations on systems
containing phosphorus that the accuracy can be further improved by employing a
larger active space.Comment: 6 pages, 5 figure
Compact and Flexible Basis Functions for Quantum Monte Carlo Calculations
Molecular calculations in quantum Monte Carlo frequently employ a mixed basis
consisting of contracted and primitive Gaussian functions. While standard basis
sets of varying size and accuracy are available in the literature, we
demonstrate that reoptimizing the primitive function exponents within quantum
Monte Carlo yields more compact basis sets for a given accuracy. Particularly
large gains are achieved for highly excited states. For calculations requiring
non-diverging pseudopotentials, we introduce Gauss-Slater basis functions that
behave as Gaussians at short distances and Slaters at long distances. These
basis functions further improve the energy and fluctuations of the local energy
for a given basis size. Gains achieved by exponent optimization and
Gauss-Slater basis use are exemplified by calculations for the ground state of
carbon, the lowest lying excited states of carbon with , ,
, symmetries, carbon dimer, and naphthalene. Basis size
reduction enables quantum Monte Carlo treatment of larger molecules at high
accuracy.Comment: 8 Pages, 2 Figures, 9 Table
Baroclinic Vorticity Production in Protoplanetary Disks; Part I: Vortex Formation
The formation of vortices in protoplanetary disks is explored via
pseudo-spectral numerical simulations of an anelastic-gas model. This model is
a coupled set of equations for vorticity and temperature in two dimensions
which includes baroclinic vorticity production and radiative cooling. Vortex
formation is unambiguously shown to be caused by baroclinicity because (1)
these simulations have zero initial perturbation vorticity and a nonzero
initial temperature distribution; and (2) turning off the baroclinic term halts
vortex formation, as shown by an immediate drop in kinetic energy and
vorticity. Vortex strength increases with: larger background temperature
gradients; warmer background temperatures; larger initial temperature
perturbations; higher Reynolds number; and higher resolution. In the
simulations presented here vortices form when the background temperatures are
and vary radially as , the initial vorticity
perturbations are zero, the initial temperature perturbations are 5% of the
background, and the Reynolds number is . A sensitivity study consisting
of 74 simulations showed that as resolution and Reynolds number increase,
vortices can form with smaller initial temperature perturbations, lower
background temperatures, and smaller background temperature gradients. For the
parameter ranges of these simulations, the disk is shown to be convectively
stable by the Solberg-H{\o}iland criteria.Comment: Originally submitted to The Astrophysical Journal April 3, 2006;
resubmitted November 3, 2006; accepted Dec 5, 200
A comparison between different cycle decompositions for Metropolis dynamics
In the last decades the problem of metastability has been attacked on
rigorous grounds via many different approaches and techniques which are briefly
reviewed in this paper. It is then useful to understand connections between
different point of views. In view of this we consider irreducible, aperiodic
and reversible Markov chains with exponentially small transition probabilities
in the framework of Metropolis dynamics. We compare two different cycle
decompositions and prove their equivalence
Sleep quality influences subsequent motor skill acquisition
While the influence of sleep on motor memory consolidation has been extensively investigated, its relation to initial skill acquisition is less well understood. The purpose of the present study was to investigate the influence of sleep quality and quantity on subsequent motor skill acquisition in young adults without sleep disorders. Fifty-five healthy adults (mean age = 23.8 years; 34 women) wore actigraph wristbands for 4 nights, which provided data on sleep patterns before the experiment, and then returned to the laboratory to engage in a motor sequence learning task (explicit 5-item finger sequence tapping task). Indicators of sleep quality and quantity were then regressed on a measure of motor skill acquisition (Gains Within Training, GWT). Wake After Sleep Onset (WASO; i.e., the total amount of time the participants spent awake after falling asleep) was significantly and negatively related to GWT. This effect was not because of general arousal level, which was measured immediately before the motor task. Conversely, there was no relationship between GWT and sleep duration or self-reported sleep quality. These results indicate that sleep quality, as assessed by WASO and objectively measured with actigraphy before the motor task, significantly impacts motor skill acquisition in young healthy adults without sleep disorders. (PsycINFO Database Record. (c) 2016 APA, all rights reserved).Accepted manuscrip
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