We wished to confirm that the algorithm maintains detailed balance and thus yields a correct Boltzmann distribution. To do this, we tested the method on a hot water gas for which the acceptance rate for new trial water positions is high, so that any error introduced by the MC procedure would be apparent from a difference in the energy distribution relative to a plain MD simulation of the same system with a suitable thermostat. The test system is composed of 97 gas phase water molecules at 500 K in a constant volume box with a side length of about 56 Å along each axis. To maximize the effect of the MC moves, we used an MC region that covered the entire simulation box.