The ice model and the eight-vertex model on the two-dimensional Sierpinski gasket

We present the numbers of ice model configurations (with Boltzmann factors equal to one) I(n) on the two-dimensional Sierpinski gasket SG(n) at stage n. The upper and lower bounds for the entropy per site, defined as lim _v→lnI(n)/v, where v is the number of vertices on SG(n), are derived in terms of the results at a certain stage. As the difference between these bounds converges quickly to zero as the calculated stage increases, the numerical value of the entropy can be evaluated with more than a hundred significant figures accuracy. The corresponding result of the ice model on the generalized two-dimensional Sierpinski gasket S^Gb(n) with b=3 is also obtained, and the general upper and lower bounds for the entropy per site for arbitrary b are conjectured. We also consider the number of eight-vertex model configurations on SG(n) and the number of generalized vertex models ^Eb(n) on S^Gb(n), and obtain exactly ^Eb(n)= 2^{2(b+1)b(b+1)/2]n}+b+4/(b+2). It follows that the entropy per site is lim_v→ln^Eb(n)/v=2(b+1)b+4ln2.