Thursday, March 14, 2013

1303.2511 (Ravindra Shinde et al.)

Large-scale first principles configuration interaction calculations of
optical absorption in aluminum clusters

Ravindra Shinde, Alok Shukla
We report the linear optical absorption spectra of aluminum clusters Al$_{n}$ (n=2--5), using systematic large-scale all-electron correlated calculations. Several low-lying isomers of each cluster were considered, and their geometries were optimized at the coupled-cluster singles doubles (CCSD) level of theory. With these optimized ground-state geometries, excited states of different clusters were computed using the multi-reference singles-doubles configuration-interaction (MRSDCI) approach, which includes electron correlation effects at a sophisticated level. These CI wave functions were used to compute the transition dipole matrix elements connecting the ground and various excited states of different clusters, eventually leading to their linear absorption spectra. The convergence of our results with respect to the basis sets, and the size of the CI expansion, was carefully examined. The contribution of configurations to many body wave function of various excited states suggests that the excitations involved are collective, and plasmonic in nature.
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