Simulations Virtual Substance

Inquiry-driven student learning of thermodynamics is achieved with the implementation of the Virtual Substance molecular dynamics simulation program. Problem solving and critical thinking skills are developed by students through the completion of the modules described in this chapter. In addition, Virtual Substance is shown to be exceptionally numerically accurate as a tool for doing authentic science. 

Virtual Substance simulations can be run using either periodic boundary conditions or fixed walls. In a fixed wall calculation, the simulation box has physical walls. The resulting system is a droplet , albeit a rectangular droplet, and as a result, the thermodynamic properties differ from those of the bulk substance. One can create a bulk substance by using periodic boundary conditions where the simulation box interacts with copies of itself repeated in three dimensions. (5) This approximates the extended nature of a bulk material, making it appear infinite, and results in better accuracy in the calculation of thermodynamic properties. 

In this lab, the students determine the compression factor, (9) Z = PV/nRT, for Argon using the hard sphere model, the soft sphere model, and the Lennard-Jones model and compare those results to the compression factor calculated using the van der Waals equation of state and experimental data obtained from the NIST (70) web site. Figure 3 shows representative results from these experiments. The numerical accuracy of the Virtual Substance program is reflected by the mapping of the Lennard-Jones simulation data exactly onto the NIST data as seen in Figure 3. 

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