Triangular-well of variable width: Theory and simulation

The use of a two-parameter potential results in a simple re-scaling of the properties of the fluid [1]. This leads to the corresponding states (CS) principle already established in the classical statistical mechanics [2]. Most of the fluids do not follow this principle so the use of a three-parameter potential is required in order to obtain deviation from the CS principle. The square-well (SW) potential of variable width is the simplest three-parameter model. This potential gives a non-conformal behavior of the fluids [1]. It has been already used to develop different equations of state and discrete potentials to model real fluids [3,4]. An alternative to the SW potential is the use of another simple model like the triangular-well (TW) potential. This potential has the advantage that it changes softly as the distance increases, which is characteristic of real fluids instead of the drastic change presented in the SW potential [2]. The TW potential of variable width has not been widely studied in the literature except for some Monte Carlo simulation results for the case of a width of two times the sphere diameter [5,6]. No equation of state (EoS) has been reported for the TW potential of variable width. In this work, an EoS for the TW of variable width based on the perturbation theory of Barker and Henderson is presented. This EoS is compared with Monte Carlo simulation results previously reported in the literature [5,6] and with new results obtained in this work by Monte Carlo simulation of the TW fluid for different potential widths.