  We report the effects of variation in length on the electronic structure of
CdSe nanorods derived from atomic clusters and passivated by fictitious
hydrogen atoms. These nanorods are augmented by attaching gold clusters at both
the ends to form a nanodumbbell. The goal is to assess the changes at nanolevel
after formation of contacts with gold clusters serving as electrodes and
compare the results with experimental observations [PRL, 95, 056805 (2005)].
Calculations involving nanorods of length 4.6 Angstrom to 116.6 Angstrom are
performed using density functional theory implemented within plane-wave basis
set. The binding energy per atom saturates for nanorod of length 116.6
Angstrom. It is interesting to note that upon attaching gold clusters, the
nanorods shorter than 27 Angstrom develop metallicity by means of metal induced
gap states (MIGS). Longer nanorods exhibit a nanoscale Schottky barrier
emerging at the center. For these nanorods, interfacial region closest to the
gold electrodes shows a finite density of states in the gap due to MIGS, which
gradually decreases towards the center of the nanorod opening up a finite gap.
Bader charge analysis indicates localized charge transfer from metal to
semiconductor.
