A new class of small carbon clusters called Fullerene, e.g. C_ discovered in 1985, is one of the most interesting nanoscale materials at present because of its unique shape and physical and chemical properties. In this paper, the electronic structure and the structural stability of the C_ microcluster are examined by means of dynamical simulated annealing. We apply mixed-basis fomalism in order to describe wave functions including accurately core and valence orbitals. The basis set of this scheme consists of both plane waves and atomic orbitals, incorporating all electrons and full-potential into calculation. The present method is superior to the standard approach using the plane wave expansion and a pseudopotential, with respect that strongly localized electron orbitals like 1s and 2p can be described with considerably limited number of basis functions
