期刊
NANOSCALE
卷 4, 期 14, 页码 4190-4198出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c2nr30253e
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- Air Force Office of Scientific Research under AFOSR Award [FA9550-09-1-0451]
- Alfred P. Sloan Foundation
- Camille and Henry Dreyfus Foundation
The excitation spectra of linear atomic chains of silver and gold with various sizes have been calculated using time-dependent density functional theory. Silver chains show longitudinal and transverse peaks as well as a low-intensity d-band. The longitudinal peak, corresponding to the HOMO-LUMO transition (along the main axis of the chain), shifts linearly to the red as the length of the system increases, consistent with the particle-in-a-box model. The transverse peak remains at approximately constant energy for all systems studied and corresponds to Sigma(m) -> Pi(m) transitions in the xy plane perpendicular to the chain. As the chain grows, transitions arising from d orbitals contribute to the transverse peak, which affects its oscillator strength. Contrary to silver, gold chains display a strong d-band that converges to a distinct pattern at a chain length of about twelve atoms. The transitions involved in the d-band originate from localized d-orbitals with a d(z2) character since they have the right symmetry to give transitions into the LUMO, LUMO + 1, ..., which have Sigma symmetry. Transitions arising from these localized d-orbitals also affect the position of the longitudinal peak and generate a wide transverse band. Although the majority of the transitions involved in the transverse band have a d Sigma -> Pi or d Pi -> Sigma character, they are hidden by much stronger excitations of d Pi -> Pi character in gold nanowires.
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