Ab initio development of generalized Lennard-Jones (Mie) force fields for predictions of thermodynamic properties in advanced molecular-based SAFT equations of state
Date:
A methodology for obtaining two-body interaction potentials from ab initio calculations is proposed for small species with interactions that are suitably described as isotropic. The corresponding force fields explicitly incorporate three-body interactions and quantum effects of fluids. The methodology provides one with a strategy to map the ab initio force field to effective Mie potentials. A density-dependent two-body approximation of the Axilrod-Teller three-body potential [1] and a temperature-dependent Feynman–Hibbs correction for an effective quantum potential [2] are used to enhance the accuracy of the Mie potentials. When the thermodynamic properties of systems characterized by these potentials are described with the SAFT-VR Mie equation of state, the reliance on thermophysical data to obtain model parameters is completely dispensed with, providing a wholly predictive platform.
The application of this approach to noble gases, using high-accuracy ab initio potentials, provides Mie potentials which are remarkably effective when implemented in SAFT-VR Mie; predictions of the vapour–liquid envelope are similar or superior to those obtained using potentials estimated from experimental thermodynamic data in the conventional fashion. Extending the methodology to an anisotropic species, methane, yields similar levels of accuracy; results are substantially better than those obtained using COSMO-RS, the only other fully predictive ab initio method for obtaining thermophysical properties (averaged error for saturation pressure 7.86% cf. 99.4%; for critical temperature 0.49% cf. 9.49%).
[1] G. Marcelli, R. J. Sadus, 2000. A link between the two-body and three-body interaction energies of fluids from molecular simulation, Journal of Chemical Physics,112, 6382–6385. [2] A. Aasen, M. Hammer, Å. Ervik, E. A. Müller, Ø. Wilhelmsen, 2019, Equation of state and force fields for Feynman-Hibbs-corrected Mie fluids. I. Application to pure helium, neon, hydrogen, and deuterium, Journal of Chemical Physics, 151, 064508.
Speaker: Tianpu Zhao