On Obtaining Boltzmann-Distributed Configurational Ensembles from Expanded Ensemble Simulations with Fast State Mixing.

In Expanded Ensemble (EXE) or Simulated Tempering simulations, the system's (effective) temperature is frequently updated to enhance configurational sampling. We investigated how short the EXE state update interval τ can become before too frequent updates impede Boltzmann sampling. Simulating alanine dipeptide in explicit water, we show that a hybrid MC/MD integrator reliably yields Boltzmann-distributed configurations regardless of τ. However, in MD-driven EXE simulations with short τ, configurational ensembles depend on the thermostat settings.