Soft mean spherical approximation

The HMSA closure (10) has been used to solve the OZ equation it is an interpolation between the soft mean spherical approximation at small r and the HNC closure at large r. 

This phenomenological treatment first employed in the mean spherical approximation [Eq.(43)J, in a form suitable for a potential made up of soft core and an attractive part [49, 50], has proven its reliability [22]. 

The mean spherical approximation (MSA) theory for fluids originated as the extension to continuum fluids of the spherical model for lattice gases. In practice it is usually applied to potentials with spherical hard cores, although extensions to soft core and non-spherical core potentials have been discussed. 

---