A theoretical study of the structures and optical spectra of helical copper–silver clusters

Abstract

The structures and optical response of helical clusters ("Bernal spirals") with compositions Ag12Cu1(+) and Ag1Cu12(+) are calculated within Kohn-Sham density functional theory and the configuration interaction singles variant of time dependent density functional theory. The effects of dopant position within the cluster on the vertical excitation spectrum are investigated according to the underlying electronic structure of the major transitions. The roles of symmetry and geometry are investigated by calculating the optical response of helical, icosahedral and nanorod-like clusters of Ag13(+), finding local structure to be significant in driving the resultant optical response at the subnanometre scale. Further, it is noted that helical clusters have optical properties which are quite distinct from those of nanorods of similar dimensions. The effect of multiple doping is studied by introducing copper atoms into the centre of the silver helix, over the composition range Ag13(+) to Ag6Cu7(+). There is a complex variation of the major plasmon-like peak over this range, attributed to subtle variations in the influence of the copper 3d band on the excitations and charge transfer for different sites within the cluster. This work suggests that coinage metal nanohelices have unusual, tunable electronic properties, which in addition to their inherent chirality makes them interesting systems to study for chiral catalysis and optoelectronics.

Optical properties of Ag–Au nanoclusters for sulphide sensing from TDDFT calculations

“…The TDDFT calculations were performed using the atomic-orbital based NWCHEM v.6.3 package [34], based on the long range corrected LC-uPBE exchange correlation functional [35]. The def2-TZVPP basis sets were used, which can give accurate treatments of the electronics by an effective core potential (ECP) replacing 28 electrons per silver and gold atom, respectively [36]. It is reported that the LC-uPBE functional combined with def2-TZVPP basis sets can successfully reproduce the experimental photo-depletion spectroscopy of the cationic Ag and Au clusters [37].…”

Optical properties of nanoalloys

“…50 This is not surprising since the relative position of d and s bands in Cu is more similar to gold than to silver. Exotic helical Ag-Cu 13-atom clusters have also been studied at the TDDFT level 54 finding that both the structure and the position of the Cu single atom dopant appreciably influenced the optical spectrum.…”

Surface plasmons in quantum-sized noble-metal clusters: TDDFT quantum calculations and the classical picture of charge oscillations

“…24,32,33 However, the spectra turn out to be rather sensitive even to rather subtle changes of the geometries. [6][7][8][9]23,24,26,[34][35][36][37][38][39] Using pseudopotentials and / or localized orbitals, the atomistic inhomogeneity of the metals can fully be taken into account. In recent years, calculations of intermediate-size noble metal clusters have been carried out using, in particular, time-dependent density-functional theory.…”

“…In recent years, calculations for intermediate-size noble metal clusters have been carried out using, in particular, time-dependent density-functional theory. [6][7][8][9]23,24,26,[34][35][36][37][38][39] Using pseudopotentials and/or localized orbitals, the atomistic inhomogeneity of the metals can fully be taken into account. Moreover, the explicit description including the d electrons has become possible although the description of the contributions of the d electrons is rather sensitive to the functionals used.…”