title: Theoretical analysis of the optical excitation spectra of silver and gold nanowires.
abstract: 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 ∑(m)→Π(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(z(2)) character since they have the right symmetry to give transitions into the LUMO, LUMO + 1, …, which have ∑ 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∑→Π or dΠ→∑ character, they are hidden by much stronger excitations of dΠ→Π character in gold nanowires.
authors.affiliation: Department of Chemistry, Kansas State University, 213 CBC Building, Manhattan, KS 66506, USA.
authors.forename: Emilie B
authors.initials: EB
authors.lastname: Guidez
authors.forename: Christine M
authors.initials: CM
authors.lastname: Aikens
mesh_terms: D006046:Gold / Q000737:chemistry*; D008962:Models, Theoretical; D053770:Nanowires / Q000737:chemistry*; D011789:Quantum Theory; D012834:Silver / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D012834:Silver; D006046:Gold