ABSTRACT
Thermodynamic potentials play a substantial role in numerous scientific disciplines and serve as basic constructs for describing the behavior of matter. Despite their significance, comprehensive investigations of their topological characteristics and their connections to molecular interactions have eluded exploration due to experimental inaccessibility issues. This study addresses this gap by analyzing the topology of the Helmholtz energy, Gibbs energy, Grand potential, and Null potential that are associated with different isothermal boundary conditions. By employing Monte Carlo simulations in the NVT, NpT, and µVT ensembles and a molecular-based equation of state, methane, ethane, nitrogen, and methanol are investigated over a broad range of thermodynamic conditions. The predictions from the two independent methods are overall in very good agreement. Although distinct quantitative differences among the fluids are observed, the overall topology of the individual thermodynamic potentials remains unaffected by the molecular architecture, which is in line with the corresponding states principle-as expected. Furthermore, a comparative analysis reveals significant differences between the total potentials and their residual contributions.
ABSTRACT
Generalized expressions for thermodynamic properties in terms of ensemble averages are discussed for adiabatic and isothermal ensembles. They are implemented in the simulation code ms2 and validated by Monte Carlo simulations for the Lennard-Jones fluid. A comparison of the eight statistical ensembles regarding size scaling behavior, convergence, and stability is provided for state points throughout the homogeneous fluid region. The resulting data are in good agreement but differ in their statistical distributions. In closed systems, the statistical quality of the data is better than in open systems. Overall, the microcanonical ensemble performs best.
