TDDFT Analysis of Optical Properties of Thiol Monolayer-Protected Gold and Intermetallic Silver鈥揋old Au144(SR)60 and Au84Ag60(SR)60 Clusters

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• 作者：Sami Malola ; Lauri Lehtovaara ; Hannu H盲kkinen
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：August 28, 2014
• 年：2014
• 卷：118
• 期：34
• 页码：20002-20008
• 全文大小：541K
• ISSN：1932-7455

文摘

The optical absorption spectra of atomistic model structures for experimentally isolated all-gold Au₁₄₄(SR)₆₀ and intermetallic Au₈₄Ag₆₀(SR)₆₀ clusters are systematically analyzed from linear-response time-dependent density functional theory (LR-TDDFT) and time-dependent density functional perturbation theory (TD-DFPT) calculations. The computed spectra, utilizing the atomistic model for Au₁₄₄(SR)₆₀ published by us in 2009, reproduce closely the experimental observations for corresponding isolated compounds, reported previously by Kumara and Dass in 2011. A collective dipole oscillation within the metal cores of the all-gold and intermetallic clusters is formed as response to light in the visible range. The weight of the oscillation and especially the screening by Au(5d) electrons are shifted gradually closer to the metal/ligand interface as the excitation energy is increased, but none of these clusters supports formation of a localized surface plasmon resonance. Based on the comparison of calculated spectra for two isomers of the intermetallic Au₈₄Ag₆₀(SR)₆₀ cluster and the previously published experimental data, one can conclude that silver preferentially occupies the core surface and induces strong radial reorganization of the electron density in the metal core. This arrangement magnifies the collective intraband (sp-electrons) dipolar response and brings up more distinct features in the absorption spectrum as compared to the all-gold case. The intrinsically chiral gold鈥搕hiolate interface of these clusters is predicted to induce strong circular dichroism (CD) signals for higher-energy excitations, below the wavelength of 500 nm.