Periodic Potts chain
= Periodic Potts chain
{title2=$E=-J\sum_{n=1}^L\delta_{\sigma_n,\sigma_{n+1}}$}
The ferromagnetic <Potts model> on a labelled ring has $Q$ possible site states, $J>0$ and $\sigma_{L+1}=\sigma_1$. Its <spin-chain transfer matrix> is $T=(e^{\beta J}-1)I+P$, with $P$ the $Q$-dimensional <all-ones matrix>. The <canonical partition function> is $(e^{\beta J}+Q-1)^L+(Q-1)(e^{\beta J}-1)^L$. The convention counts two bonds when $L=2$.