An improved first-order mean spherical approximation theory for the square-shoulder fluid

Abstract

The theory, which utilizes an exponential enhancement of the first-order mean spherical approximation (FMSA) for the radial distribution functions of the hard-core plus square-well fluid, is adopted to study the properties of the simplest model of the core-softened fluids, i.e., the hard spheres with a square-shoulder interaction. The results for structure and thermodynamic properties are reported and compared against both the Monte Carlo simulation data as well as with those obtained within the conventional FMSA theory. We found that in the region of low densities and low temperatures, where the conventional FMSA theory fails, the exponential-based FMSA theory besides being qualitatively correct also provides with a notable quantitative improvement of the theoretical description.

Theoretical approaches to the structural properties of the square-shoulder fluid

“…On the other hand, the curves corresponding to the SEXP/FMSA displayed in those figures of Ref. [24] exhibit a higher discrepancy with respect to simulation data than in our Figures 1, 3 and 4. This is due to the fact that, through an involuntary mistake in Ref.…”

“…[24]. On the other hand, the curves corresponding to the SEXP/FMSA displayed in those figures of Ref.…”

“…In this paper we have revisited three analytical procedures [23,24,29,30,32] to obtain the structural properties of SS fluids and compared their predictions against simulation results [12,19,21] in order to assess their merits and limitations. All these approaches have in common the fact that they are analytical in Laplace space and reduce in two independent limits [see Equations (2a) and (2b)] to the PY result for the HS fluid, although only the RFA does it in a third limit [see Equation (2c)].…”

“…Due to the fact that they are not very illuminating and may be found elsewhere [24], they will be omitted here. Alternatively, G 1 (s) can be numerically inverted [39] to obtain g 1 (r).…”

“…More re-cently, Hlushak et al [24] considered both the Tang-Lu first-order mean spherical approximation(FMSA) [28][29][30][31] and its associated simplified exponential approximation (SEXP/FMSA) [32] for the RDF of the SS fluid and reported additional MC data for the system. These three approaches (FMSA, SEXP/FMSA and RFA) are formulated in terms of the Laplace transform…”