APS Excellence in Physics Education Award
November 2019

Science SPORE Prize
November 2011

The Open Source Physics Project is supported by NSF DUE-0442581.

## Lennard-Jones PVT System Model Documents

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#### Main Document

##### Lennard-Jones PVT System Model

written by Wolfgang Christian

The Lennard-Jones PVT System simulates a 2D system of particles confined between a thermal reservoir and a piston.   This computer model is designed to study the equation of state for particles interacting via a simple but realistic molecular potential that has a weak long-range attraction and a strong short range repulsion.   Slow-moving particles are color-coded as blue and fast particles are color-coded as yellow.  Users can set the initial particle energy, the initial particle separation, and the thermal reservoir temperature Tr.  The thermal conductivity parameter ? determines the probability that a collision with the thermal wall will affect (thermalize) the colliding particle.  If the conductivity is one, the particle velocity after a reservoir collision is set according to Maxwell-Boltzmann statistics.  If the conductivity is zero, all reservoir collisions are elastic and the total internal energy E of the system is conserved.

The piston input fields in the bottom panel are used to compress and expand the system.  Users can approximate an adiabatic compression by setting ?=0 and can approximate an isothermal compression by setting ?=1. The piston speed must, of course, be small to insure that the system remains in equilibrium during the compression for a (quasi-static approximation) reversible process.  Separate windows allow users to follow the change in state of the system on a PV plot or a time evolution plot.

The Lennard-Jones PVT model is a supplemental simulation for the article "Pressure Oscillations in Adiabatic Compression" by Roland Stout in The Physics Teacher 49(5), 280-281 (2011) and has been approved by the author and The Physics Teacher editor.  The model was developed using the Easy Java Simulations (Ejs) modeling tool and is distributed as a ready-to-run (compiled) Java archive.  Double clicking the  ejs_stp_md_LennardJonesPVTSystem.jar file will run the program if Java is installed.