TD-DFT and TD-DFTB Investigation of the Optical Properties and Electronic Structure of Silver Nanorods and Nanorod Dimers

Abstract

Here, we perform theoretical investigation using time-dependent density functional theory (TD-DFT) and time-dependent density functional tight binding (TD-DFTB) for the electronic structure and optical properties of silver nanorods. TD-DFTB generally performs well for the accurate description of optical properties with respect to the size and type of dimer assembly of silver nanorods compared to TD-DFT. However, the energies and intensities of the longitudinal and transverse peaks of the nanorods are somewhat underestimated with TD-DFTB compared to the values calculated at the TD-DFT level. By exploiting the computational efficiency of TD-DFTB, we also extend our investigation to longer nanorods and their dimers containing up to ∼2000 atoms. Our results show that the coupling between nanorods and the resulting optical properties of the dimer assemblies are quite dependent on the length of the monomers. In all cases, the energy shifts in dimers as a function of the gap distance deviate significantly from the dipole–dipole interaction model. Moreover, a comparison of the best-fit curves for the dependence of the fractional shifts (Δλ/λ0) on nanorod length indicates that the parameters of the plasmon ruler equation depend on the length of the nanorods and the type of the assembly rather than approaching a universal value. These insights are enabled by the computational efficiency of TD-DFTB and its ability to treat quantum mechanical effects in large nanorod dimer systems.

Charge-transfer plasmons with narrow conductive molecular bridges: A quantum-classical theory

“…It has been shown, for example, that Ag-Au nanoparticles are very sensitive to the chemical configuration, and in some cases the position of the atomic species outweigh the effect of changing composition 31 . Density Functional based Tight Binding (DFTB) methods have been used, for example, for study of optical properties and electronic structure of Ag nanorods and nanorod dimers 54 and for description of influence of quantum tunneling on the efficiency of excitation energy transfer in plasmonic Ag NPs chain waveguides 55 . TDDFT and DFTB, being quantum methods, are, however, very time-consuming methods and the possibility of their practical use strongly depends on the size of the NPs, i.e.…”

Plasmon-induced hot-carrier generation differences in gold and silver nanoclusters

“…[2][3][4][5][6][7][8] Such optical properties have been intensely studied both experimentally and theoretically in the last decades. 2,3,5,6,[8][9][10][11] The intense color that colloidal solutions of noble metal nanostructures often exhibit stems from its interaction with electromagnetic radiation which induces collective oscillation of conduction band (CB) electrons, this phenomenon is known as Localized Surface Plasmon Resonance (LSPR) or simply Surface Plasmon Resonance (SPR). The existence of this phenomenon makes possible that these particles absorb very large amounts of electromagnetic radiation and concentrate it in a very localized space region which is less than its physical dimensions.…”

Plasmon-Induced Hot-Carrier Generation differences in Gold and Silver Nanoclusters

“…[2][3][4][5][6][7][8] Such optical properties have been intensely studied both experimentally and theoretically in the last decades. 2,3,5,6,[8][9][10][11] The intense color that colloidal solutions of noble metal nanostructures often exhibit stems from its interaction with electromagnetic radiation which induces collective oscillation of conduction band (CB) electrons, this phenomenon is known as Localized Surface Plasmon Resonance (LSPR) or simply Surface Plasmon Resonance (SPR). The existence of this phenomenon makes possible that these particles absorb very large amounts of electromagnetic radiation and concentrate it in a very localized space region which is less than its physical dimensions.…”