  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.
