ORDER-N TIGHT-BINDING MOLECULAR-DYNAMICS - APPLICATION TO GIANT FULLERENES

We present a molecular dynamics study of the energetics and structures of very large carbon cage clusters, which has been performed using ti ght-binding methods, both empirical and ab initio. The use of an order -N scheme, which provides the solution of the electronic problem with an effort proportional to the size of the system, allowed us to study carbon cage clusters with up to 3840 atoms using workstation HP755 (51 2MB). We have considered clusters with spherical and with toroidal top ology, and systematically find that spherical clusters have lower ener gy than toroidal clusters of the same size. However, the toroidal C-36 0 and larger clusters have lower energy per atom than the fullerene C- 60, and therefore should be possible to be synthesized. Concerning the spherical carbon cage clusters, we show that, in all cases, their min imum energy shape is markedly polyhedral rather than spherical. The cl usters present nearly flat faces between each three protruding pentago n sites. The surfaces are nevertheless smooth, without sharp edges in the lines joining the pentagons, which would be present in a perfect t runcated icosahedron.