638 research outputs found
The open XXZ-chain: Bosonisation, Bethe ansatz and logarithmic corrections
We calculate the bulk and boundary parts of the free energy for an open
spin-1/2 XXZ-chain in the critical regime by bosonisation. We identify the
cutoff independent contributions and determine their amplitudes by comparing
with Bethe ansatz calculations at zero temperature T. For the bulk part of the
free energy we find agreement with Lukyanov's result [Nucl.Phys.B 522, 533
(1998)]. In the boundary part we obtain a cutoff independent term which is
linear in T and determines the temperature dependence of the boundary
susceptibility in the attractive regime for . We further show that at
particular anisotropies where contributions from irrelevant operators with
different scaling dimensions cross, logarithmic corrections appear. We give
explicit formulas for these terms at those anisotropies where they are most
important. We verify our results by comparing with extensive numerical
calculations based on a numerical solution of the T=0 Bethe ansatz equations,
the finite temperature Bethe ansatz equations in the quantum-transfer matrix
formalism, and the density-matrix renormalisation group applied to transfer
matrices.Comment: 35 pages, 8 figure
Lattice Gas Dynamics; Application to Driven Vortices in Two Dimensional Superconductors
A continuous time Monte Carlo lattice gas dynamics is developed to model
driven steady states of vortices in two dimensional superconducting networks.
Dramatic differences are found when compared to a simpler Metropolis dynamics.
Subtle finite size effects are found at low temperature, with a moving smectic
that becomes unstable to an anisotropic liquid on sufficiently large length
scales.Comment: 5 pages, 4 figure
A Rapid Dynamical Monte Carlo Algorithm for Glassy Systems
In this paper we present a dynamical Monte Carlo algorithm which is
applicable to systems satisfying a clustering condition: during the dynamical
evolution the system is mostly trapped in deep local minima (as happens in
glasses, pinning problems etc.). We compare the algorithm to the usual Monte
Carlo algorithm, using as an example the Bernasconi model. In this model, a
straightforward implementation of the algorithm gives an improvement of several
orders of magnitude in computational speed with respect to a recent, already
very efficient, implementation of the algorithm of Bortz, Kalos and Lebowitz.Comment: RevTex 7 pages + 4 figures (uuencoded) appended; LPS preprin
Lattice path integral approach to the one-dimensional Kondo model
An integrable Anderson-like impurity model in a correlated host is derived
from a gl(21)-symmetric transfer matrix by means of the
Quantum-Inverse-Scattering-Method (QISM). Using the Quantum Transfer Matrix
technique, free energy contributions of both the bulk and the impurity are
calculated exactly. As a special case, the limit of a localized moment in a
free bulk (Kondo limit) is performed in the Hamiltonian and in the free energy.
In this case, high- and low-temperature scales are calculated with high
accuracy.Comment: 26 pages, 9 figure
Local Inhomogeneity in Asymmetric Simple Exclusion Processes with Extended Objects
Totally asymmetric simple exclusion processes (TASEP) with particles which
occupy more than one lattice site and with a local inhomogeneity far away from
the boundaries are investigated. These non-equilibrium processes are relevant
for the understanding of many biological and chemical phenomena. The
steady-state phase diagrams, currents, and bulk densities are calculated using
a simple approximate theory and extensive Monte Carlo computer simulations. It
is found that the phase diagram for TASEP with a local inhomogeneity is
qualitatively similar to homogeneous models, although the phase boundaries are
significantly shifted. The complex dynamics is discussed in terms of
domain-wall theory for driven lattice systems.Comment: 11 pages, 5 figure
Bethe Ansatz study of one-dimensional Bose and Fermi gases with periodic and hard wall boundary conditions
We extend the exact periodic Bethe Ansatz solution for one-dimensional bosons
and fermions with delta-interaction and arbitrary internal degrees of freedom
to the case of hard wall boundary conditions. We give an analysis of the ground
state properties of fermionic systems with two internal degrees of freedom,
including expansions of the ground state energy in the weak and strong coupling
limits in the repulsive and attractive regimes.Comment: 27 pages, 6 figures, key reference added, typos correcte
Finite temperature Drude weight of an integrable Bose chain
We study the Drude weight at finite temperatures of an integrable
bosonic model where the particles interact via nearest-neighbour coupling on a
chain. At low temperatures, is shown to be universal in the sense that
this region is equivalently described by a Gaussian model. This low-temperature
limit is also relevant for the integrable one-dimensional Bose gas. We then use
the thermodynamic Bethe ansatz to confirm the low-temperature result, to obtain
the high temperature limit of and to calculate numerically.Comment: 11 pages, 2 figure
Performance Limitations of Flat Histogram Methods and Optimality of Wang-Landau Sampling
We determine the optimal scaling of local-update flat-histogram methods with
system size by using a perfect flat-histogram scheme based on the exact density
of states of 2D Ising models.The typical tunneling time needed to sample the
entire bandwidth does not scale with the number of spins N as the minimal N^2
of an unbiased random walk in energy space. While the scaling is power law for
the ferromagnetic and fully frustrated Ising model, for the +/- J
nearest-neighbor spin glass the distribution of tunneling times is governed by
a fat-tailed Frechet extremal value distribution that obeys exponential
scaling. We find that the Wang-Landau algorithm shows the same scaling as the
perfect scheme and is thus optimal.Comment: 5 pages, 6 figure
Soft versus Hard Dynamics for Field-driven Solid-on-Solid Interfaces
Analytical arguments and dynamic Monte Carlo simulations show that the
microstructure of field-driven Solid-on-Solid interfaces depends strongly on
the dynamics. For nonconservative dynamics with transition rates that factorize
into parts dependent only on the changes in interaction energy and field
energy, respectively (soft dynamics), the intrinsic interface width is
field-independent. For non-factorizing rates, such as the standard Glauber and
Metropolis algorithms (hard dynamics), it increases with the field.
Consequences for the interface velocity and its anisotropy are discussed.Comment: 9 pages LaTex with imbedded .eps figs. Minor revision
Exchange Monte Carlo for Molecular Simulations with Monoelectronic Hamiltonians
We introduce a general Monte Carlo scheme for achieving atomistic simulations
with monoelectronic Hamiltonians including the thermalization of both nuclear
and electronic degrees of freedom. The kinetic Monte Carlo algorithm is used to
obtain the exact occupation numbers of the electronic levels at canonical
equilibrium, and comparison is made with Fermi-Dirac statistics in infinite and
finite systems. The effects of a nonzero electronic temperature on the
thermodynamic properties of liquid silver and sodium clusters are presented
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