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

TL;DR

This study performs large-scale, highly correlated calculations to analyze the optical absorption spectra of boron clusters B$_{n}$ (n=2--5), revealing collective plasmonic excitations through advanced quantum chemistry methods.

Contribution

It introduces a comprehensive computational approach combining CCSD and MRSDCI methods to accurately predict optical properties of boron clusters, considering multiple isomers and electron correlation effects.

Findings

Optical absorption spectra vary with cluster size and isomer.

Excited states exhibit collective, plasmonic character.

Results demonstrate convergence with basis set and CI expansion size.

Abstract

We have performed systematic large-scale all-electron correlated calculations on boron clusters B$_{n}$(n=2--5), to study their linear optical absorption spectra. Several possible isomers of each cluster were considered, and their geometries were optimized at the coupled-cluster singles doubles (CCSD) level of theory. Using the 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 were carefully examined. The contribution of configurations to many body wavefunction of various excited states suggests that the excitations involved are collective, plasmonic type.