  The electronic and magnetic properties of carbon nanobuds have been
investigated using density functional theory. The carbon nanobuds are formed by
attaching smaller fullerenes (C20, C28, C36 and C40) of variable size with
(5,5) ACNT and (5,0) ZCNT. Fullerenes interact strongly with CNT surface having
binding energies within the range -0.93eV to -4.06eV. The C-C bond lengths near
the attachment region increase from the original C-C bond lengths. The relative
stabilities of the nanobuds are closely related to C-C bond lengths and bond
angles in cycloaddition reaction. Nanobuds formed by bond cycloaddition are
energetically most favorable amongst all cycloadditions. The electronic and
magnetic properties of nanobuds depend strongly on electronic properties of its
building blocks. The attachment of C20 and C40 on CNTs open up the HOMO-LUMO
gaps of nanobuds whereas C28 and C36 results in addition of impurity states
near the Fermi level. The total magnetic moment of nanobuds vary from
0.28{\mu}B to 4.00{\mu}B which depend on the nature of bonding between
fullerene and CNTs. The results outline the potential of nanobuds as hybrid
carbon nanostructures and how their properties can be tuned with the size and
type of fullerene attached.
