Double Potts chain and exact results for some two-dimensional spin models

An exact analytical solution for the q-state Potts model on a 2 x infinity ladder with arbitrary two-, three-, and four-site interactions in a unit ce ll in presented is a closed form. This solution is used to show that the fi nite-size internal energy equation [6] yields an accurate value of the crit ical temperature for the triangular Potts lattice with three-site interacti ons in alternate triangular faces. It is argued that the above equation is exact at least for self-dual models on isotopic strips. (C) 2001 MAIK "Nauk a/Interperiodica".