A computational (quantum-chemical) experiment has been performed on constructing a silicon nanofiber by gas-phase deposition. A model of two-step polymerization has been proposed in which a fullerene Si60 molecule serves as the main structural unit. The formation of oligomers of the molecule containing from three to eight molecular units explains the discrete values of the liber width observed experimentally. The formation of a "rouleau" of oligomers leads to fiber growth in terms of length. It is shown that both steps are favorable in energy with the decisive superiority of a high-spin state, which poses the question of considering silicon nanofibers to be molecular magnets. © 2001 MAIK "Nauka/Interperiodica".