  It is shown how to derive simple polynomial expressions for the variational
configurational entropy starting from the cluster variation method (CVM). As an
example, first six terms of the expansion of the entropy in powers of the
nearest-neighbour (NN) short-range order (SRO) parameter are obtained for the
NN Ising ferromagnet on the face-centered cubic lattice using the tetrahedron
(T-CVM) approximation. Calculated values of the transition temperature and the
NN SRO parameter at the transition converge rapidly to their T-CVM counterparts
as order of the approximation increases.
