Hyperbolic analogues of fullerenes on orientable surfaces

Mathematical models of fullerenes are cubic spherical maps of type (5, 6), that is, with pentagonal and hexagonal faces only. Any such map necessarily contains exactly 12 pentagons, and it is known that for any integer alpha >= 0 except alpha = 1 there exists a fullerene map with precisely alpha hexagons. In this paper we consider hyperbolic analogues of fullerenes, modelled by cubic maps of face-type (6, k) for some k >= 7 on an orientable surface of genus at least 2. The number of k-gons in this case depends on the genus but the number of hexagons is again independent of the surface. We focus on the values of k that are 'universal' in the sense that there exist cubic maps of face-type (6, k) for all genera g >= 2. By Euler's formula, if k is universal, then k is an element of {7, 8, 9, 10, 12, 18}. We show that for any k is an element of {7, 8, 9, 12, 18} and any g >= 2 there exists a cubic map of face-type (6, k) with any prescribed number of hexagons. Fork = 7 and 8 we also prove the existence of polyhedral cubic maps of face-type (6, k) on surfaces of any prescribed genus g >= 2 and with any number of hexagons alpha, except for the cases k = 8, g = 2 and alpha <= 2, where we show that no such maps exist. (C) 2011 Elsevier B.V. All rights reserved.