Theoretical analysis of the optical excitation spectra of silver and gold nanowires
Theoretical analysis of the optical excitation spectra of silver and gold nanowires
复制标题
DOI：
10.1039/c2nr30253e
复制
发表时间：
2012-01-01
期刊：
影响因子：
6.7
通讯作者：
Aikens, Christine M.
中科院分区：
文献类型：
--
作者：
Guidez, Emilie B.;Aikens, Christine M.
用含时密度泛函理论计算了不同尺寸的银和金线性原子链的激发光谱。银链显示纵向和横向峰以及低强度d带。对应于HOMO-LUMO转变（沿着链的主轴）的纵向峰随着系统长度的增加线性地向红色移动，与盒中粒子模型一致。对于所研究的所有系统，横向峰保持在近似恒定的能量，并且对应于垂直于链的xy平面中的Sigma（m）-> Pi（m）跃迁。随着链的增长，从d轨道产生的跃迁有助于横向峰，这影响其振子强度。与银相反，金链显示出一个强的d带，在链长约为12个原子时会收敛成一个独特的模式。d带中涉及的跃迁源自具有d（z2）特征的定域d轨道，因为它们具有正确的对称性以给出到LUMO，LUMO + 1，...，具有Sigma对称性。从这些本地化的d-轨道所产生的过渡也影响的纵向峰的位置，并产生一个宽的横向带。虽然在横向带中涉及的大多数跃迁具有d σ-> Pi或d Pi -> σ特征，但是它们被金纳米线中d Pi -> Pi特征的强得多的激发所隐藏。
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.