Transfer matrices for the zero-temperature Potts antiferromagnet on cyclic and Möbius lattice strips

We present transfer matrices for the zero-temperature partition function of the q-state Potts antiferromagnet (equivalently, the chromatic polynomial) on cyclic and Möbius strips of the square, triangular, and honeycomb lattices of width L_y and arbitrarily great length L_x. We relate these results to our earlier exact solutions for square-lattice strips with L_y = 3, 4, 5, triangular-lattice strips with L_y = 2, 3, 4, and honeycomb-lattice strips with L_y = 2, 3 and periodic or twisted periodic boundary conditions. We give a general expression for the chromatic polynomial of a Möbius strip of a lattice A and exact results for a subset of honeycomb-lattice transfer matrices, both of which are valid for arbitrary strip width L_y. New results are presented for the L_y = 5 strip of the triangular lattice and the L_y = 4 and L_y = 5 strips of the honeycomb lattice. Using these results and taking the infinite-length limit L_x → ∞, we determine the continuous accumulation locus of the zeros of the above partition function in the complex q plane, including the maximal real point of nonanalyticity of the degeneracy per site, W as a function of q.