In principle, MD or Monte Carlo simulations can accurately estimate EOS

properties for arbitrary gas compositions and arbitrary thermodynamic

conditions. In practice, people rarely do so. Here are the reasons that I

can think of, in order of decreasing importance:

1. Interatomic potentials;

a. These are often developed for condensed phases and so may not be

particularly accurate for gases. For example, the second virial coefficient

at 300K may be off by 10% or more.

b. They are usually developed for pure species. Mixture interactions are

computed using binary mixing rules, analogous to those used in

equations-of-state.

2. Statistical uncertainty: These methods are based on statistical sampling,

and so the accuracy converges rather slowly ~ 1/sqrt(CPU time)

3. If all you care about is macroscopic properties, it does not make sense

to use a method that is primarily concerned with microscopic properties.

Given all this, I think you would be better off taking your presumably

accurate pure-component CEOS functions and estimating the necessary binary

mixing parameters, and then using these to describe the multicomponent

mixtures. Don't they teach that in chemical engineering schools anymore?

:-).

Finally, always check your results against any available experimental data.

Good luck!

Aidan