  We study the optical properties of small gold chains doped with different
transition metal (TM) atoms (Ni,Rh,Fe) by using the time-dependent
density-functional theory (TDDFT) approach. The optical absorption spectrum of
such systems demonstrates a collective plasmon mode when the number of atoms is
larger than approximately 10, and this mode splits into two peaks when the Au
chain is doped with some of the TM (Ni,Fe) atoms. We associate the additional
peak with a local plasmonic mode which corresponds to the charge oscillations
around the potential created by the d-orbitals of the impurity atoms. The
effect takes place when the number of TM atoms is much smaller than the number
of Au atoms. This behavior is opposite to the case of larger bulk
noble-metal-TM clusters (radius $>$1nm), where the doping with TM atoms does
not lead to any generation of additional modes, and often leads to a
suppression of the main plasmon peak. This phenomenon of tuning the optical
properties of nanosystems with transition metal atoms can be used in many
practical applications in the field of nanotechnology.
