Title: Semiempirical Modeling of Ag Nanoclusters: New Parameters for Optical Property Studies Enable Determination of Double Excitation Contributions to Plasmonic Excitation

Abstract

Quantum mechanical studies of Ag nanoclusters have shown that plasmonic behavior can be modeled in terms of excited states where collectivity among single excitations leads to strong absorption. However, new computational approaches are needed to provide understanding of plasmonic excitations beyond the single-excitation level. We show that semiempirical INDO/CI approaches with appropriately selected parameters reproduce the TD-DFT optical spectra of various closed-shell Ag clusters. The plasmon-like states with strong optical absorption comprise linear combinations of many singly excited configurations that contribute additively to the transition dipole moment, whereas all other excited states show significant cancellation among the contributions to the transition dipole moment. The computational efficiency of this approach allows us to investigate the role of double excitations at the INDO/SDCI level. The Ag cluster ground states are stabilized by slight mixing with doubly excited configurations, but the plasmonic states generally retain largely singly excited character. The consideration of double excitations in all cases improves the agreement of the INDO/CI absorption spectra with TD-DFT, suggesting that the SDCI calculation effectively captures some of the ground-state correlation implicit in DFT. Furthermore, these results provide the first evidence to support the commonly used assumption that single excitations are in many cases sufficientmore » to describe the optical spectra of plasmonic excitations quantum mechanically.« less

Authors:

Gieseking, Rebecca L. ^[1]; Ratner, Mark A. ^[1]; Schatz, George C. ^[1]

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+ Show Author Affiliations

1. Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States

Publication Date:

2016-06-23

Research Org.:

Northwestern Univ., Evanston, IL (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1258703

Alternate Identifier(s):

OSTI ID: 1268309

Grant/Contract Number:  

FG02-10ER16153

Resource Type:

Published Article

Journal Name:

Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

Additional Journal Information:

Journal Name: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory Journal Volume: 120 Journal Issue: 26; Journal ID: ISSN 1089-5639

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

74 ATOMIC AND MOLECULAR PHYSICS