3,318 research outputs found
How to mesh up Ewald sums (II): An accurate error estimate for the P3M algorithm
We construct an accurate estimate for the root mean square force error of the
particle-particle-particle-mesh (P3M) algorithm by extending a single particle
pair error measure which has been given by Hockney and Eastwood. We also derive
an easy-to-use analytic approximation to the error formula. This allows a
straightforward and precise determination of the optimal splitting parameter
(as a function of system specifications and P3M parameters) and hence knowledge
of the force accuracy prior to the actual simulation. The high quality of the
estimate is demonstrated in several examples.Comment: 9 pages, 7 figures included, revtex styl
Estimate of the Cutoff Errors in the Ewald Summation for Dipolar Systems
Theoretical estimates for the cutoff errors in the Ewald summation method for
dipolar systems are derived. Absolute errors in the total energy, forces and
torques, both for the real and reciprocal space parts, are considered. The
applicability of the estimates is tested and confirmed in several numerical
examples. We demonstrate that these estimates can be used easily in determining
the optimal parameters of the dipolar Ewald summation in the sense that they
minimize the computation time for a predefined, user set, accuracy.Comment: 22 pages, 6 figures, Revtex style, submitted to J. Chem. Phy
Polyelectrolytes in Solution - Recent Computer Simulations
We present a short overview over recent MD simulations of systems of fully
flexible polyelectrolyte chains with explicitly treated counter ions using the
full Coulomb potential. The main emphasis is given on the conformational
properties of the polymers, with a short discussion on counter ion
condensation.Comment: 10 pages, including 5 figures, to appear in the proceedings of the
50th Yamada Conference on Polyelectrolytes, Inuyama, Japan (1998
Fixed versus random triangulations in 2D simplicial Regge calculus
We study 2D quantum gravity on spherical topologies using the Regge calculus
approach with the measure. Instead of a fixed non-regular triangulation
which has been used before, we study for each system size four different random
triangulations, which are obtained according to the standard Voronoi-Delaunay
procedure. We compare both approaches quantitatively and show that the
difference in the expectation value of between the fixed and the random
triangulation depends on the lattice size and the surface area . We also try
again to measure the string susceptibility exponents through a finite-size
scaling Ansatz in the expectation value of an added interaction term in
an approach where is held fixed. The string susceptibility exponent
is shown to agree with theoretical predictions for the sphere,
whereas the estimate for appears to be too negative.Comment: 4 latex pages + 4 ps-figs. + espcrc2.sty, poster presented by W.
Janke at LATTICE96(gravity
Strongly Charged, Flexible Polyelectrolytes in Poor Solvents -- Molecular Dynamics Simulations
We present a set of molecular dynamics (MD) simulations of strongly charged,
flexible polyelectrolyte chains under poor solvent conditions in a salt free
solution. Structural properties of the chains and of the solutions are
reported. By varying the polymer density and the electrostatic interaction
strength we study the crossover from a dominating electrostatic interaction to
the regime of strong screening, where the hydrophobic interactions dominate.
During the crossover a multitude of structures is observed. In the limit of low
polymer density strongly stretched, necklace like conformations are found. In
the opposite limit of high polymer density which is equivalent to strongly
screened electrostatic interactions, we find that the chains are extremely
collapsed, however we observe no agglomeration or phase separation. The
investigations show that the density of free charges is one of the relevant
parameters which rules the behavior of the system and hence should be used as a
parameter to explain experimental results.Comment: 42 pages, including 22 figures and 2 table
Strong electrostatic interactions in spherical colloidal systems
We investigate spherical macroions in the strong Coulomb coupling regime
within the primitive model in salt-free environment. We first show that the
ground state of an isolated colloid is naturally overcharged by simple
electrostatic arguments illustrated by the Gillespie rule. We furthermore
demonstrate that in the strong Coulomb coupling this mechanism leads to ionized
states and thus to long range attractions between like-charged spheres. We use
molecular dynamics simulations to study in detail the counterion distribution
for one and two highly charged colloids for the ground state as well as for
finite temperatures. We compare our results in terms of a simple version of a
Wigner crystal theory and find excellent qualitative and quantitative
agreement.Comment: 30 pages and 17 PS figures. REVTEX. Minor changes. To appear in Phys
Rev
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