Accurate lower bounds on two-dimensional constraint capacities from   corner transfer matrices
  We analyse the capacity of several two-dimensional constraint families - the exclusion, colouring, parity and charge model families. Using Baxter's corner transfer matrix formalism combined with the corner transfer matrix renormalisation group method of Nishino and Okunishi, we calculate very tight lower bounds and estimates on the growth rate of these models. Our results strongly improve previous known lower bounds, and lead to the surprising conjecture that the capacity of the even and charge(3) constraints are identical. 
Yao-ban Chan and Andrew Rechnitzer
math.CO cond-mat.stat-mech