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

Area of Science:

• Computational chemistry
• Molecular dynamics
• Statistical mechanics

Background:

• Expanded Ensemble (EXE) and Simulated Tempering simulations are used to improve configurational sampling.
• Frequent temperature updates are key to enhancing sampling in these methods.
• Understanding the impact of the temperature update interval (τ) is crucial for accurate simulations.

Purpose of the Study:

• To investigate the minimum effective state update interval (τ) in EXE simulations before it hinders Boltzmann sampling.
• To determine if short τ values in MD-driven EXE simulations affect configurational ensembles.
• To compare the reliability of different integrators under varying τ conditions.

Main Methods:

• Simulations of alanine dipeptide in explicit water.
• Utilizing Expanded Ensemble (EXE) simulations with varying state update intervals (τ).
• Employing both hybrid Monte Carlo/Molecular Dynamics (MC/MD) and standard MD integrators.
• Analyzing configurational ensembles and their distribution relative to thermostat settings.

Main Results:

• A hybrid MC/MD integrator consistently produced Boltzmann-distributed configurations irrespective of the τ value.
• MD-driven EXE simulations with short τ intervals showed that configurational ensembles are sensitive to thermostat settings.
• The study identified a critical threshold for τ where sampling may become compromised in certain simulation setups.

Conclusions:

• Hybrid MC/MD integrators offer robustness in maintaining Boltzmann sampling even with very short EXE state update intervals.
• Thermostat choice is a critical parameter in MD-driven EXE simulations when employing short temperature update intervals.
• Careful consideration of τ and thermostat settings is necessary for accurate configurational sampling in EXE simulations.