31,642 research outputs found
The band gap problem: the accuracy of the Wien2k code confronted
This paper is a continuation of our detailed study [Phys. Rev. B 86, 195106
(2012)] of the performance of the recently proposed modified Becke-Jonhson
potential (mBJLDA) within the known Wien2k code. From the 41 semiconductors
that we have considered in our previous paper to compute the band gap value, we
selected 27 for which we found low temperature experimental data in order to
pinpoint the relative situation of the newly proposed Wien2k(mBJLDA) method as
compared to other methods in the literature. We found that the GWA gives the
most accurate predictions. The Wien2k (mBJLDA) code is slightly less precise,
in general. The Hybrid functionals are less accurate, on the overall. The GWA
is definitely the most precise existing method nowadays. In 88% of the
semiconductors considered the error was less than 10%. Both, the GWA and the
mBJLDA potential, reproduce the band gap of 15 of the 27 semiconductors
considered with a 5% error or less. An extra factor to be taken into account is
the computational cost. If one would seek for precision without taking this
factor into account, the GWA is the method to use. If one would prefer to
sacrifice a little the precision obtained against the savings in computational
cost, the empirical mBJLDA potential seems to be the appropriate method. We
include a graph that compares directly the performance of the best three
methods, according to our analysis, for each of the 27 semiconductors studied.
The situation is encouraging but the problem is not yet a closed issue.Comment: 8 pages, 1 figur
Cellular automaton supercolliders
Gliders in one-dimensional cellular automata are compact groups of
non-quiescent and non-ether patterns (ether represents a periodic background)
translating along automaton lattice. They are cellular-automaton analogous of
localizations or quasi-local collective excitations travelling in a spatially
extended non-linear medium. They can be considered as binary strings or symbols
travelling along a one-dimensional ring, interacting with each other and
changing their states, or symbolic values, as a result of interactions. We
analyse what types of interaction occur between gliders travelling on a
cellular automaton `cyclotron' and build a catalog of the most common
reactions. We demonstrate that collisions between gliders emulate the basic
types of interaction that occur between localizations in non-linear media:
fusion, elastic collision, and soliton-like collision. Computational outcomes
of a swarm of gliders circling on a one-dimensional torus are analysed via
implementation of cyclic tag systems
Lagrangian Volume Deformations around Simulated Galaxies
We present a detailed analysis of the local evolution of 206 Lagrangian
Volumes (LVs) selected at high redshift around galaxy seeds, identified in a
large-volume cold dark matter (CDM) hydrodynamical
simulation. The LVs have a mass range of . We
follow the dynamical evolution of the density field inside these initially
spherical LVs from up to , witnessing highly
non-linear, anisotropic mass rearrangements within them, leading to the
emergence of the local cosmic web (CW). These mass arrangements have been
analysed in terms of the reduced inertia tensor , focusing on the
evolution of the principal axes of inertia and their corresponding
eigendirections, and paying particular attention to the times when the
evolution of these two structural elements declines. In addition, mass and
component effects along this process have also been investigated. We have found
that deformations are led by dark matter dynamics and they transform most of
the initially spherical LVs into prolate shapes, i.e. filamentary structures.
An analysis of the individual freezing-out time distributions for shapes and
eigendirections shows that first most of the LVs fix their three axes of
symmetry (like a skeleton) early on, while accretion flows towards them still
continue. Very remarkably, we have found that more massive LVs fix their
skeleton earlier on than less massive ones. We briefly discuss the
astrophysical implications our findings could have, including the galaxy
mass-morphology relation and the effects on the galaxy-galaxy merger parameter
space, among others.Comment: 23 pages, 20 figures. Minor editorial improvement
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