327 research outputs found
Molecular dynamics investigations on a quantum system in a thermostat
The model quantum system of fermions in a one dimensional harmonic oscillator
potential is investigated by a molecular dynamics method at constant
temperature. Although in quantum mechanics the equipartition theorem cannot be
used like in the Nose-Hoover-thermostat it is possible to couple an additional
degree of freedom to the system which acts as a thermometer and drives the
system towards the desired temperature via complex time steps.Comment: 11 pages, 8 postscript figures, uses 'epsfig.sty'. Submitted to
PHYSICA A. More information available at
http://obelix.physik.uni-osnabrueck.de/~schnac
Bulk Properties of Anharmonic Chains in Strong Thermal Gradients: Non-Equilibrium Theory
We study nonequilibrium properties of a one-dimensional lattice Hamiltonian
with quartic interactions in strong thermal gradients. Nonequilibrium
temperature profiles, T(x), are found to develop significant curvature and
boundary jumps. From the determination of the bulk thermal conductivity, we
develop a quantitative description of T(x) including the jumps.Comment: 14pp, 5 fig
Non-Equilibrium Statistical Mechanics of Classical Lattice Field Theory
Classical theory in weak and strong thermal gradients is studied on
the lattice in (1+1) dimensions. Classical theory in weak and strong
thermal gradients is studied on the lattice in (1+1) dimensions. The steady
state physics of the theory is investigated from first principles and
classified into dynamical regimes. We derive the bulk properties associated
with thermal transport, and explore in detail the non-equilibrium statistical
mechanics of the theory as well as connections to equilibrium and irreversible
thermodynamics. Linear response predictions are found to be valid for systems
quite far from equilibrium and are seen to eventually break down simultaneously
with local equilibrium.Comment: 28 pages, 20 fig
Global Demons in Field Theory : Critical Slowing Down in the Xy Model
We investigate the use of global demons, a `canonical dynamics', as an
approach to simulating lattice regularized field theories. This
deterministically chaotic dynamics is non-local and non-Hamiltonian, and
preserves the canonical measure rather than . We apply this
inexact dynamics to the 2D XY model, comparing to various implementations of
hybrid Monte Carlo, focusing on critical exponents and critical slowing down.
In addition, we discuss a scheme for making energy non-conserving dynamical
algorithms exact without the use of a Metropolis hit.Comment: 23 pages text plus 12 figures [Submitted to Nuc. Phys. B, 7/92
Nose-Hoover dynamics for coherent states
The popular method of Nose and Hoover to create canonically distributed
positions and momenta in classical molecular dynamics simulations is
generalized to a genuine quantum system of infinite dimensionality. We show
that for the quantum harmonic oscillator, the equations of motion in terms of
coherent states can easily be modified in an analogous manner to mimic the
coupling of the system to a thermal bath and create a quantum canonical
ensemble. Possible applications to more complex systems, especially interacting
Fermion systems, are proposed.Comment: 13 pages, 3 figure
Dynamical Symmetry Approach to Periodic Hamiltonians
We show that dynamical symmetry methods can be applied to Hamiltonians with
periodic potentials. We construct dynamical symmetry Hamiltonians for the Scarf
potential and its extensions using representations of su(1,1) and so(2,2).
Energy bands and gaps are readily understood in terms of representation theory.
We compute the transfer matrices and dispersion relations for these systems,
and find that the complementary series plays a central role as well as
non-unitary representations.Comment: 20 pages, 7 postscript figure
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