The novel electronic, optical and super-conducting properties exhibited by C60 and its assembled materials have greatly stimulated the scientists all over the world racing to study Si60. In this paper we performed an extensive search from eighteen isomers including cages, wires, and stuffed structures of Si. It is found that the fullerene cage is not stable, and the tricapped-trigonal-prism unit is not the structural unit for Si 60. While the spherical compact structure is the most stable energetically, in agreement with experiments which suggested a transition from the elongated geometry to a more spherical one for the medium sized Si clusters [J. Chem. Phys. 111 (1999) 7865, J. Chem. Phys. 117 (2002) 3219].