Variational renormalisation-group approach to the q-state Potts model in two dimensions

The two-dimensional q-state Potts model is investigated by means of a Kadanoff lower-bound renormalisation-group transformation that utilises a recent suggestion to identify disordered cells with vacancies. The topology of the phase diagram is obtained, including first- and second-order transitions for q>qc and q<or=qc, respectively, as well as accurate results for critical and tricritical exponents and the critical value qc.

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