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  An alternative procedure consists in carrying out 
  molecular simulations, where both the solvent and solute 
  are treated explicitly. After a rigorous averaging over 
  the solvent conﬁgurations, a coarse-grained description 
  of the ions, which still includes the eﬀect of the solvent 
  structure, can be obtained [8–11]. However, this set of 
  methods is purely numeric; they do not provide any an- 
  alytical expression for thermodynamic quantities. They 
  are therefore restricted to simple geometries [12, 13] (bulk 
  solutions or planar interfaces). The description of com- 
  plex systems, such as porous or electrochemical materi- 
  als, is still based on continuous solvent models [14]. 
  
  In this letter we present a method aimed at bridging 
  the gap between analytical and numerical approaches. It 
  is based on the application of liquid perturbation theory 
  (LPT) [15] to eﬀective ion-ion potentials extracted from 