455 research outputs found
Computer Simulations of Quantum Chains
We report recent progress in computer simulations of quantum systems
described in the path-integral formulation. For the example of the
quantum chain we show that the accuracy of the simulation may greatly be
enhanced by a combination of multigrid update techniques with a refined
discretization scheme. This allows us to assess the accuracy of a variational
approximation.Comment: 5 pages, LaTeX + 2 postscript figures. Talk presented by TS at "Path
Integrals from meV to MeV: Dubna '96". See also
http://www.cond-mat.physik.uni-mainz.de/~janke/doc/home_janke.htm
Shape anisotropy of polymers in disordered environment
We study the influence of structural obstacles in a disordered environment on
the size and shape characteristics of long flexible polymer macromolecules. We
use the model of self-avoiding random walks on diluted regular lattices at the
percolation threshold in space dimensions d=2, 3. Applying the Pruned-Enriched
Rosenbluth Method (PERM), we numerically estimate rotationally invariant
universal quantities such as the averaged asphericity A_d and prolateness S of
polymer chain configurations. Our results quantitatively reveal the extent of
anisotropy of macromolecules due to the presence of structural defects.Comment: 8 page
From particle condensation to polymer aggregation
We draw an analogy between droplet formation in dilute particle and polymer
systems. Our arguments are based on finite-size scaling results from studies of
a two-dimensional lattice gas to three-dimensional bead-spring polymers. To set
the results in perspective, we compare with in part rigorous theoretical
scaling laws for canonical condensation in a supersaturated gas at fixed
temperature, and derive corresponding scaling predictions for an undercooled
gas at fixed density. The latter allows one to efficiently employ parallel
multicanonical simulations and to reach previously not accessible scaling
regimes. While the asymptotic scaling can not be observed for the comparably
small polymer system sizes, they demonstrate an intermediate scaling regime
also observable for particle condensation. Altogether, our extensive results
from computer simulations provide clear evidence for the close analogy between
particle condensation and polymer aggregation in dilute systems.Comment: 10 pages, 6 figure
Monte Carlo Study of Pure-Phase Cumulants of 2D q-State Potts Models
We performed Monte Carlo simulations of the two-dimensional q-state Potts
model with q=10, 15, and 20 to study the energy and magnetization cumulants in
the ordered and disordered phase at the first-order transition point .
By using very large systems of size 300 x 300, 120 x 120, and 80 x 80 for q=10,
15, and 20, respectively, our numerical estimates provide practically (up to
unavoidable, but very small statistical errors) exact results which can serve
as a useful test of recent resummed large-q expansions for the energy cumulants
by Bhattacharya `et al.' [J. Phys. I (France) 7 (1997) 81]. Up to the third
order cumulant and down to q=10 we obtain very good agreement, and also the
higher-order estimates are found to be compatible.Comment: 18 pages, LaTeX + 2 postscript figures. To appear in J. Phys. I
(France), May 1997 See also
http://www.cond-mat.physik.uni-mainz.de/~janke/doc/home_janke.htm
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