Non-ideal Mixing Effects in the H-He EOS

It has been shown that, because of interactions at atomic and molecular levels, the behaviour of a mixture of hydrogen and helium cannot be accurately represented by considering these elements separately. Using on the one hand ab initio simulations which involve a system of interacting hydrogen and helium particles and pure equations of state for hydrogen and helium on the other, we derive the contributions in density and entropy of the interactions between hydrogen and helium particles.