In order to understand the stability of polyhedral hydrocarbons with their curvatures, a systematic study was performed on polyhedral hydrocarbons (CH) (n = 4, 6, 8, 20, 40, 60, 80, 100) by employing combined ab initio Hartree-Fock and density functional theory method. The calculated results demonstrate that energy per C-H unit (E-n,C-H) in polyhedral hydrocarbons undergoes a decrease and then an increase with their curvatures unexpectedly and C20H20-I-h with curvature satisfying spa hybridization is most stable. Structural analysis reveals that the a-a interaction, instead of ring strain or pyramidalization of angles dominates the stability of these polyhedral hydrocarbons. (c) 2006 Elsevier B.V. All rights reserved.