This calculator is based on the Lennard-Jones equation of state of Johnson, et al. (1993) and calculates the
reduced Helmholtz energy per atom (Ar*/N), reduced pressure (P*), reduced internal energy per atom (U*/N)
and reduced Gibbs energy per atom (Gr*/N) based on inputs of the reduced density (ρ*) and reduced temperature
(T*). I got tired of implementing it in multiple places every time I needed it, so hopefully this web-based
form will be useful for others too. The equation is a modified Benedict-Webb-Rubin EOS with 32 adjustable parameters
and was parameterized from a bunch of MC and MD simulation data. Because this EOS is not flat enough in the critical
region, predictions are not necessarily accurate in the vicinity of the critical point. For actual simulation results,
you are encouraged to check the NIST LJ benchmarks and the excellent work of Errington with TMMC.