Bulk, surface and corner free energy series for the chromatic polynomial on the square and triangular lattices

Jesper Jacobsen (1)

1 LPTENS - Laboratoire de Physique Théorique de l'ENS [École Normale Supérieure]

We present an efficient algorithm for computing the partition function of the q-colouring problem (chromatic polynomial) on regular two-dimensional lattice strips. Our construction involves writing the transfer matrix as a product of sparse matrices, each of dimension ~ 3^m, where m is the number of lattice spacings across the strip. As a specific application, we obtain the large-q series of the bulk, surface and corner free energies of the chromatic polynomial. This extends the existing series for the square lattice by 32 terms, to order q^{-79}. On the triangular lattice, we verify Baxter's analytical expression for the bulk free energy (to order q^{-40}), and we are able to conjecture exact product formulae for the surface and corner free energies.

Domaines: Mécanique statistique [cond-mat.stat-mech]; Physique mathématique [math-ph]; Physique mathématique [math-ph]

Jesper Jacobsen. Bulk, surface and corner free energy series for the chromatic polynomial on the square and triangular lattices. 2010. ⟨hal-00484977v2⟩