818 research outputs found
Metastable states as a key to the dynamics of supercooled liquids
Computer simulations of a model glass-forming system are presented, which are
particularly sensitive to the correlation between the dynamics and the
topography of the potential energy landscape. This analysis clearly reveals
that in the supercooled regime the dynamics is strongly influenced by the
presence of deep valleys in the energy landscape, corresponding to long-lived
metastable amorphous states. We explicitly relate non-exponential relaxation
effects and dynamic heterogeneities to these metastable states and thus to the
specific topography of the energy landscape
Energy Barriers and Activated Dynamics in a Supercooled Lennard-Jones Liquid
We study the relation of the potential energy landscape (PEL) topography to
relaxation dynamics of a small model glass former of Lennard-Jones type. The
mechanism under investigation is the hopping betweem superstructures of PEL
mimima, called metabasins (MB). From the mean durations \tauphi of visits to
MBs, we derive effective depths of these objects by the relation
\Eapp=\d\ln\tauphi/\d\beta, where \beta=1/\kB T. Since the apparent
activation energies \Eapp are of purely dynamical origin, we look for a
quantitative relation to PEL structure. A consequence of the rugged nature of
MBs is that escapes from MBs are not single hops between PEL minima, but
complicated multi-minima sequences. We introduce the concept of return
probabilities to the bottom of MBs in order to judge whether the attraction
range of a MB was left. We then compute the energy barriers that were
surmounted. These turn out to be in good agreement with the effective depths
\Eapp, calculated from dynamics. Barriers are identified with the help of a
new method, which accurately performs a descent along the ridge between two
minima. A comparison to another method is given. We analyze the population of
transition regions between minima, called basin borders. No indication for the
mechanism of diffusion to change around the mode-coupling transition can be
found. We discuss the question whether the one-dimensional reaction paths
connecting two minima are relevant for the calculation of reaction rates at the
temperatures under study.Comment: 17 pages, 16 figure
- …