Rigorous expressions for thermodynamic properties in the NpH ensemble

Area of Science:

• Thermodynamics
• Statistical Mechanics
• Computational Chemistry

Background:

• Thermodynamic properties are crucial for understanding fluid behavior.
• Calculating these properties in specific ensembles, like the isoenthalpic-isobaric ensemble, presents computational challenges.
• Existing methods often require computationally intensive derivatives of potential energy functions.

Purpose of the Study:

• To derive novel molecular expressions for thermodynamic properties and entropy derivatives in the isoenthalpic-isobaric ensemble.
• To develop a method that simplifies calculations by avoiding volume derivatives of potential energy.
• To validate the new expressions using computational simulations.

Main Methods:

• Utilizing Lustig's methodology for microcanonical and canonical ensembles.
• Expressing thermodynamic properties via phase-space functions (derivatives of phase-space volume).
• Employing Monte Carlo simulations for validation.

Main Results:

• Derived molecular expressions for thermodynamic properties and entropy derivatives up to third order.
• Expressions depend only on ensemble averages of kinetic energy and volume.
• Successfully validated the method for a Lennard-Jones fluid model.

Conclusions:

• The derived expressions offer a computationally efficient route to thermodynamic properties in the isoenthalpic-isobaric ensemble.
• This approach is particularly beneficial for simulations using accurate ab initio potentials.
• The method provides a robust alternative for molecular simulations of fluid systems.