  We extend results of R. Holley beyond the integer lattice to a large class of
groups which includes free groups. In particular we show that a shift-invariant
measure is Gibbs if and only if it is Glauber-invariant. Moreover, any
shift-invariant measure converges weakly to the set of Gibbs measures when
evolved under Glauber dynamics. These results are proven using a new notion of
free energy density relative to a sofic approximation by homomorphisms. Any
measure which minimizes free energy density is Gibbs.
