In most core-collapse supernova (SN) simulations, the equation of state (EoS) has been usually modelled within the single-nucleus approximation. In this approach, the ensemble of nuclei expected to be present in the medium is replaced by one (average) nucleus. Although this approximation is adequate to predict thermodynamic properties of the medium in the temperature-density range of interest, a full statistical distribution is required to properly describe microscopic processes where reaction rates on specific nuclei are required (e.g., the electron capture).
In this contribution, a formalism to include a cluster distribution within the Nuclear Statistical Equilibrium (NSE) model in an EoS of hot stellar matter at subsaturation density is presented. A particular case, where this method is applied to an EoS for supernova simulations, will be discussed.