Use of the charged-hard-sphere reference system in variational thermodynamic calculations

We draw attention to a new reference system. This is a system of charged hard spheres embedded in a rigid, uniform, and neutralizing background. The model is attractive since analytical expressions such as the free energy, internal energy, structure factor, etc., are available. The usefulness of the model as applied to the variational study of thermodynamic properties of liquid alkali metals is explored. This model is then compared with similar thermodynamic calculations using separately the neutral hard spheres and the classical one-component plasma as reference systems. Results from this comparison show that the charged-hard-sphere system may be preferred as a reference liquid over the neutral-hard-sphere system or, from the economical and computational viewpoint, over the one-component-plasma system.