Ground state entropy of Potts antiferromagnets and the approach to the two-dimensional thermodynamic limit

We study the ground state degeneracy per site (exponent of the ground state entropy) [formula presented] for the [formula presented]-state Potts antiferromagnet on infinitely long strips with width [formula presented] of 2D lattices Λ with free and periodic boundary conditions in the [formula presented] direction, denoted [formula presented] and [formula presented] We show that the approach of [formula presented] to its 2D thermodynamic limit as [formula presented] increases is quite rapid; for moderate values of [formula presented] and [formula presented] [formula presented] is within about 5% and [formula presented] of the 2D value [formula presented] for [formula presented] and [formula presented] respectively. The approach of [formula presented] to the 2D thermodynamic limit is proved to be monotonic (nonmonotonic) for [formula presented] [formula presented] It is noted that ground state entropy determinations on infinite strips can be used to obtain the central charge for cases with critical ground states.