A method for evaluating the energy stability of carbon nanoclusters is proposed. The stabilities of the nanoclusters with different structures, such as diamond and graphite, tubulenes and graphite, are compared. Two series of stable clusters with new structures, namely, alm-ene and alm-ine, are derived. A comparison is performed for small graphite clusters containing boron atoms that play a significant role in the reaction of fullerene formation.