Molecular thermodynamics of a quantum Lennard-Jones fluid using an effective Mie potential and the SAFT-VR-Mie approach

Abstract

The SAFT-VR-Mie approach is applied to model quantum fluids following a method presented previously on the combined use of thermodynamic perturbation theory (TPT) and path-integral Monte Carlo (PIMC) simulations to describe a quantum square-well (QSW) fluid. In this communication we consider a system of N particles contained within a volume V interacting via a quantum Lennard-Jones potential (QLJ) with de Broglie's thermal wavelength , where m denotes the particle's mass, T is the temperature and h and k are the Planck's and Boltzmann's constants, respectively. The method is based on the exact analogy between the discretised path-integral formalism of Quantum Mechanics and the partition function of a classical system composed of necklace molecules. The Zwanzig's expansion is implemented in order to obtain the QLJ's first-perturbation term, , from PIMC simulations. An effective Mie potential with a variable repulsive parameter range and fixed attractive parameter, , is obtained by mapping to the classical expression provided by the SAFT-VR-Mie value, . The thermodynamics of the QLJ system is obtained using the SAFT-VR-Mie equation of state and applied to obtain accurate predictions for molecular hydrogen's isotherms when .