Based on calculations using density functional theory, we proposed a series of open heterofullerenes: C56N2O, C56N2S, C56P2O, and C56P2S, which constitute the first examples of open heterofullerenes not externally functionalized. They exhibit large HOMO-LUMO gaps which are comparable to that for C-60. The Fermi level of the system becomes higher as the heterofullerene changes from C56N2O to C56P2S. In the solid-state, face centered cubic structures are more stable than body centered cubic for all of them. In addition, we have also investigated other heterofullerenes with empty sites (=C54N4 and C48N8). (c) 2007 Elsevier B.V. All rights reserved.