1,898 research outputs found
Ab initio quantum transport through armchair graphene nanoribbons: Streamlines in the current density
We calculate the local current density in pristine armchair graphene
nanoribbons (AGNRs) with varying width, , employing a
density-functional-theory-based ab initio transport formalism. We observe very
pronounced current patterns (streamlines) with threefold periodicity in
. They arise as a consequence of quantum confinement in the
transverse flow direction. Neighboring streamlines are separated by stripes of
almost vanishing flow. As a consequence, the response of the current to
functionalizing adsorbates is very sensitive to their placement: adsorbates
located within the current filaments lead to strong backscattering, while
adsorbates placed in other regions have almost no impact at all.Comment: 7 pages, 11 figure
Ab initio spin-flip conductance of hydrogenated graphene nanoribbons: Spin-orbit interaction and scattering with local impurity spins
We calculate the spin-dependent zero-bias conductance in
armchair graphene nanoribbons with hydrogen adsorbates employing a DFT-based ab
initio transport formalism including spin-orbit interaction. We find that the
spin-flip conductance can reach the same order of
magnitude as the spin-conserving one, , due to
exchange-mediated spin scattering. In contrast, the genuine spin-orbit
interaction appears to play a secondary role, only
A piece of cake: the ground-state energies in gamma_i-deformed N=4 SYM theory
In the non-supersymmetric gamma_i-deformed N=4 SYM theory, the scaling
dimensions of the operators tr[Z^L] composed of L scalar fields Z receive
finite-size wrapping and prewrapping corrections in the 't Hooft limit. In this
paper, we calculate these scaling dimensions to leading wrapping order directly
from Feynman diagrams. For L>=3, the result is proportional to the maximally
transcendental `cake' integral. It matches with an earlier result obtained from
the integrability-based Luescher corrections, TBA and Y-system equations. At
L=2, where the integrability-based equations yield infinity, we find a finite
rational result. This result is renormalization-scheme dependent due to the
non-vanishing beta-function of an induced quartic scalar double-trace coupling,
on which we have reported earlier. This explicitly shows that conformal
invariance is broken - even in the 't Hooft limit.Comment: 21 pages, LaTeX, BibTeX, pstricks, feynm
The complete one-loop dilatation operator of planar real beta-deformed N=4 SYM theory
We determine the missing finite-size corrections to the asymptotic one-loop
dilatation operator of the real -deformed SYM theory for
the gauge groups and in the 't Hooft limit. In the case,
the absence of the field components leads to a new kind of finite-size
effect, which we call prewrapping. We classify which states are potentially
affected by prewrapping at generic loop orders and comment on the necessity to
include it into the integrability-based description. As a further result, we
identify classes of -point correlation functions which at all loop orders in
the planar theory are given by the values of their undeformed counterparts.
Finally, we determine the superconformal multiplet structure and one-loop
anomalous dimensions of all single-trace states with classical scaling
dimension .Comment: Latex, feynmp, pstricks, 37 pages, 6 tables, v2: formulations
improved, references added, typos corrected, v3: typos corrected, matches
published versio
Readdressing the trade effect of the Euro: Allowing for currency misalignment
We know that euro-area member countries have absorbed asymmetric shocks in ways that are inconsistent with a common nominal anchor. Based on a reformulation of the gravity model that allows for such bilateral misalignment, we disentangle the conventional trade cost channel and trade effects deriving from 'implicit currency misalignment'. Econometric estimation reveals that the currency misalignment channel exerts a significant trade effect on bilateral exports. We retrieve country specific estimates of the euro effect on trade based on misalignment. This reveals asymmetric trade effects and heterogeneous outlooks across countries for the costs and benefits from adopting the euro. --Euro,gravity model,exchange rates,purchasing power parity,trade imbalances
Fast evaluation of solid harmonic Gaussian integrals for local resolution-of-the-identity methods and range-separated hybrid functionals
An integral scheme for the efficient evaluation of two-center integrals over
contracted solid harmonic Gaussian functions is presented. Integral expressions
are derived for local operators that depend on the position vector of one of
the two Gaussian centers. These expressions are then used to derive the formula
for three-index overlap integrals where two of the three Gaussians are located
at the same center. The efficient evaluation of the latter is essential for
local resolution-of-the-identity techniques that employ an overlap metric. We
compare the performance of our integral scheme to the widely used Cartesian
Gaussian-based method of Obara and Saika (OS). Non-local interaction potentials
such as standard Coulomb, modified Coulomb and Gaussian-type operators, that
occur in range-separated hybrid functionals, are also included in the
performance tests. The speed-up with respect to the OS scheme is up to three
orders of magnitude for both, integrals and their derivatives. In particular,
our method is increasingly efficient for large angular momenta and highly
contracted basis sets.Comment: 18 pages, 2 figures; accepted manuscript. v2: supplementary material
include
Finding the ground state of the Hubbard model by variational methods on a quantum computer with gate errors
A key goal of digital quantum computing is the simulation of fermionic
systems such as molecules or the Hubbard model. Unfortunately, for present and
near-future quantum computers the use of quantum error correction schemes is
still out of reach. Hence, the finite error rate limits the use of quantum
computers to algorithms with a low number of gates. The variational Hamiltonian
ansatz (VHA) has been shown to produce the ground state in good approximation
in a manageable number of steps. Here we study explicitly the effect of gate
errors on its performance. The VHA is inspired by the adiabatic quantum
evolution under the influence of a time-dependent Hamiltonian, where the -
ideally short - fixed Trotter time steps are replaced by variational
parameters. The method profits substantially from quantum variational error
suppression, e.g., unitary quasi-static errors are mitigated within the
algorithm. We test the performance of the VHA when applied to the Hubbard model
in the presence of unitary control errors on quantum computers with realistic
gate fidelities.Comment: 5+1 pages, 2 figures, 3 table
Mass wasting at the base of the South central Chilean continental margin: the Reloca Slide
Offshore south central Chile (35° S–42° S), the morphology of the lowermost continental slope and trench floor witnesses a voluminous submarine mass-wasting event. The blocky slide body deposited in the Chile Trench at 73°46´ W 35°35´ S was targeted for study during RRS JAMES COOK Cruise JC23 and termed Reloca Slide. Its size of about 24 km3, its steep and high headscarp, the spatial distribution of slide deposits and the cohesive nature of major slide blocks make it interesting to address the issue of tsunami generation. We have obtained seismic reflection data that partly reveal the internal structure of the slide body. Gravity core samples were retrieved that will allow the slide to be dated and linked to the history of sedimentation and slope stability along this particular segment of the Chilean convergent margin. At present we assume a Holocene age for the sliding event
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