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

Abstract

We report the linear optical absorption spectra of aluminum clusters Al n (n=2-5) involving valence transitions, computed using the large-scale all-electron configuration interaction (CI) methodology. 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, and thus their photoabsorption spectra. The convergence of our * To whom correspondence should be addressed † Electronic Supplementary Information (ESI) available: A detailed information about wave functions of excited states contributing to various photoabsorption peaks is presented in the supplementary information (Table I Bombay, Mumbai, Maharashtra 400076, India. Fax: +91 22 2576 7552; Tel: +91 22 2576 7576; E-mail: shukla@phy.iitb.ac.in 1 results with respect to the basis sets, and the size of the CI expansion, was carefully examined. Our results were found to be significantly different as compared to those obtained using time-dependent density functional theory (TDDFT) [Deshpande et al. Phys. Rev. B, 2003, 68, 035428]. When compared to available experimental data for the isomers of Al 2 and Al 3 , our results are in very good agreement as far as important peak positions are concerned. The contribution of configurations to many body wavefunction of various excited states suggests that in most cases optical excitations involved are collective, and plasmonic in nature.

First principles electron-correlated calculations of optical absorption in magnesium clusters

“…Furthermore, wherever possible, the results have been compared with the available literature. In earlier works, we reported similar calculations of optical absorption spectra of various isomers of small boron and aluminum clusters [12,13].…”

“…The transition dipole moment matrix elements are calculated using these ground-and excited-state wavefunctions, and are subsequently utilized to compute linear optical absorption spectrum assuming a Lorentzian line shape. The numerical approach described here has been extensively used in our earlier works dealing with the optical properties of conjugated polymers [16][17][18][19][20], as well as atomic clusters [12,13]. For the smallest cluster, namely, Mg dimer, it was possible to use the full CI approach, within the frozen-core approximation.…”

A Global Optimizer for Nanoclusters

“…We have built the global minimum structures of Al nanoclusters up to Al 12 with PyAR|XTB, and up to Al 8 with PyAR|BP86. There are several theoretical studies on Al clusters at various levels of theory, such as Sutton-Chen empirical potential (Joswig and Springborg, 2003), DFT (Ahlrichs and Elliott, 1999; Rao and Jena, 1999), and CCSD(T) (Shinde and Shukla, 2014; López-Estrada and Orgaz, 2015).…”

Ab initio Calculations of Optical Properties of Clusters

“…Using this approach, we have reported results of such calculation on small boron and aluminum clusters. 165,190 In this chapter, we present results of systematic calculations of optical absorption in various low-lying isomers of magnesium clusters using ab initio large-scale MRSDCI method. The nature of optical excitations involved in absorption has also been inves-tigated by analyzing the wavefunctions of the excited states.…”