Optical absorption in boron clusters B$_{6}$ and B$_{6}^{+}$ : A first   principles configuration interaction approach
  The linear optical absorption spectra in neutral boron cluster B$_{6}$ and cationic B$_{6}^{+}$ are calculated using a first principles correlated electron approach. The geometries of several low-lying isomers of these clusters were optimized at the coupled-cluster singles doubles (CCSD) level of theory. With these optimized ground-state geometries, excited states of different isomers were computed using the singles configuration-interaction (SCI) approach. The many body wavefunctions of various excited states have been analysed and the nature of optical excitation involved are found to be of collective, plasmonic type. 
Ravindra Shinde and Alok Shukla
physics.atm-clus cond-mat.mes-hall