A linked-cluster type of series expansion of the free energy with a variational parameter is developed to the eighth order for the q-state Potts model. The order parameter and the internal energy are then derived. By analyzing these series expansions, critical temperatures ${\mathit{T}}_{\mathit{c}}$, latent heats, and discontinuities of the order parameters at ${\mathit{T}}_{\mathit{c}}$ are determined for the cubic lattices.

• Received 28 November 1994

DOI:https://doi.org/10.1103/PhysRevB.52.39