  We have performed atomistic simulations for cylindrical multi-shell
(CMS)-type Cu nanowires containing defects. Our investigation has revealed some
physical properties that have not been detected in previous studies that have
considered defect-free nanowires. Since the vacancy formation energy is lowest
in the core of a CMS-type nanowire, a vacancy formed in the outer shell of a
CMS-type nanowire naturally migrates toward the core. The maximum of the
formation energy of an adhered atom on the surface of a CMS-type nanowire was
modeled using a 16-11-6-1 nanowire. The formation energy of an adhered atom
decreased when the diameter of the CMS-type nanowire was either above or below
the diameter of the peak energy maximum. This investigation found three
recombination mechanisms for the vacancy-adhered atom pairs: (i) by direct
recombination, (ii) by a kick-in recombination, and (iii) by a ring
recombination. Vacancy formation energy calculations show that an onion-like
cluster with a hollow was formed, and molecular dynamics simulations for
various CMS-type nanowires found that vacancies migrated towards the core. From
these, we obtained basic information on the formation of hollow CMS-type metal
nanowires (metal nanotubes) [Y. Oshima, et al., Phys. Rev. B 65, 121401
(2002)].
