of equilibrium, and therefore we cannot really tell if there is an underlying true thermodynamic transition.

One way to see that the system is falling out of equilibrium is to plot the inherent structure energy per particle [@Stillinger82; @Stillinger84; @Sastry98]. An inherent structure is a particular system configuration whose energy corresponds to the minimum of a basin in the energy landscape. The energy landscape is a 3N dimensional surface defined by the potential energy of the system which is a function of the particles’ coordinates. During each run we sampled the configurations found at each temperature. Each configuration lies somewhere in a basin and we used the method of conjugate gradients [@Press92] to find the inherent structure energy of that basin. The result is shown in Figure \[fig:inherent\_structure\] where we plot the average inherent structure energies versus the temperature of the configuration that was originally saved. At high temperatures the inherent structure energy $e_{IS}$ per particle is flat as a function of temperature. As the system is cooled, $e_{IS}$ decreases rather steeply [@Sastry98]. The inherent structure energy flattens off at low temperatures where the system has fallen out of equilibrium and has become stuck in one basin. For each measuring 