The Screened Cluster equation of state (SC EOS ) is a very accurate equation of state for hydrogen and hydrogen-helium mixtures for thermodynamical conditions typical of stars. This equation of state is

Exact at some order and based only on first principles
The SC EOS is obtained from a systematic expansion of the grand-potential Ω = –PV of the quantum gas mixture with respect to particle fugacities. Exact formal expressions are known for all terms in this expansion.
Modular
Physical effects can be turned on/off by adding/suppressing terms in the expansion of the grand-potential.
Highly accurate
No approximate effective potentials between ionized particles and atoms/molecules/ions are used.
These interactions (and shifts and broadening of spectral lines) are treated by computing exactly, at low activities, "partition" functions for clusters of few particles interacting via screened Coulomb interactions.
Open :
The method is fully explained, source code is available.
Questions? Contact Vincent Ballenegger or Angel Alastuey

Financial supports from the CNRS, the région Franche-Comté and the OSU-THETA are gratefully acknowledged.