Finite Systems under Pressure: Assessing Volume Definition Models from Parallel-Tempering Monte Carlo Simulations

Area of Science:

• Computational chemistry and physics
• Statistical mechanics
• Nanoscale science

Background:

• Predicting structural phase transitions in molecular clusters under varying conditions is essential.
• Handling simulations in the isothermal-isobaric ensemble, especially at non-zero pressures, presents challenges in defining system volume.

Purpose of the Study:

• To investigate and compare various volume models for parallel-tempering Monte Carlo (PTMC) simulations of molecular clusters.
• To analyze the impact of different volume definitions on predicting pressure-induced structural phase transitions.

Main Methods:

• Implementation of PTMC simulations treating pressure implicitly via volume.
• Application of diverse volume models: container-volume, particle-volume, average-volume, ellipsoids-volume, and convex hull-volume.
• Analysis of temperature and pressure effects on heat capacity and energy-volume correlations, using multiple-histogram methods for phase diagram construction.

Main Results:

• Significant differences were observed in simulation outcomes based on the chosen volume model.
• The study identified various pressure-induced phase transformations, including solid-solid, solid-liquid, and liquid-gas-like transitions.
• Phase diagrams for the (H2O)12 water cluster were constructed, revealing model-dependent transition behaviors.

Conclusions:

• The choice of volume model critically influences the prediction of phase transitions in molecular cluster simulations.
• Accurate volume definition is paramount for reliable simulations of nanoscale systems under pressure.
• The findings provide insights into pressure-induced structural dynamics and phase behavior of molecular clusters.