The contribution of electron-atom interaction to the equation of state for partially ionized hydrogen plasma is studied using the cluster-virial expansion. Experimental phase-shifts as well as phase-shifts calculated on the basis of different pseudopotential models are used as an input for the Beth-Uhlenbeck formula. Avoiding any ill-founded input quantities, the Beth-Uhlenbeck second virial coefficient for the electron-atom interaction, presented here for the first time, can be considered as a benchmark for other, semi-empirical approaches.
