The HS-WCA-LJ Monte Carlo Model performs simultaneous canonical Monte Carlo (MC) simulations of 108, 256 or 500 particles interacting through the hard sphere (HS), the Weeks, Chandler and Andersen (WCA) and the Lennard-Jones (LJ) pair potentials. It was inspired by the review of Chandler, Weeks and Anderson on WCA theory, illustrating that "the attractive interactions help fix the volume of the system, but the arrangements and motions of molecules within that volume are determined primarily by the local packing and steric effects produced by the repulsive forces". The radial distribution functions for the three systems are plotted after every MC cycle, at densities and temperatures chosen by the user, and the data Tables display thermodynamic results from the LJ and WCA potentials. The thermodynamics of the HS system was addressed to another application cataloged at Open Source Physics.
The objective of this application is: (i) to illustrate the canonical MC method with three different systems;(ii) to probe the densities and temperatures at which the HS and WCA potentials approach the structure(defined by the radial distribution functions) of the LJ system, regarding their use in perturbation theory.

The HS-WCA-LJ Monte Carlo Model was developed using the Easy Java Simulations (EJS) modeling tool.  It is distributed as a ready-to-run (compiled) Java archive.   Double clicking the jar file will run the program if Java is installed.  You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Please note that this resource requires at least version 1.6 of Java (JRE).