15 research outputs found
Comment on "Large Difference in the Elastic Properties of fcc and hcp Hard-Sphere Crystals"
As is well known, hard-sphere crystals of the fcc and hcp type differ very
little in their thermodynamic properties. Nonetheless, recent computer
simulations by Pronk and Frenkel indicate that the elastic response to
mechanical deformation of the two types of crystal should be quite different.
By invoking a geometrical argument put forward by R. Martin some time ago, we
suggest that this is largely due to the different symmetries of the fcc and hcp
crystal structures. Indeed, we find that elastic constants obtained by means of
computer simulations for the fcc hard-sphere crystal can be mapped onto the
equivalent ones of the hcp crystal to very high accuracy. The same procedure
applied to density functional theoretical predictions for the elastic
properties of the fcc hard-sphere crystal also produces remarkably accurate
predictions for those of the hcp hard-sphere crystal.Comment: 7 pages, 5 figure
Dynamical chaos and power spectra in toy models of heteropolymers and proteins
The dynamical chaos in Lennard-Jones toy models of heteropolymers is studied
by molecular dynamics simulations. It is shown that two nearby trajectories
quickly diverge from each other if the heteropolymer corresponds to a random
sequence. For good folders, on the other hand, two nearby trajectories may
initially move apart but eventually they come together. Thus good folders are
intrinsically non-chaotic. A choice of a distance of the initial conformation
from the native state affects the way in which a separation between the twin
trajectories behaves in time. This observation allows one to determine the size
of a folding funnel in good folders. We study the energy landscapes of the toy
models by determining the power spectra and fractal characteristics of the
dependence of the potential energy on time. For good folders, folding and
unfolding trajectories have distinctly different correlated behaviors at low
frequencies.Comment: 8 pages, 9 EPS figures, Phys. Rev. E (in press