First-principles absorption spectra of Cun(n=2–20) clusters

Abstract

Optical absorption spectra for the computed ground state structures of copper clusters (Cun, n = 2 − 20) are investigated from first principles using time-dependent density functional theory in the adiabatic local density approximation (TDLDA). The results are compared with available experimental data, existing calculations, and with results from our previous computations on silver and gold clusters. The main effects of d electrons on the absorption spectra, quenching the oscillator strengths and getting directly involved in low-energy excitations, increase in going from Agn to Aun to Cun due to the increase in the hybridization of the occupied, yet shallow, d orbitals and the partially occupied s orbitals. We predict that while Cu nanoparticles of spherical or moderately ellipsoidal shape do not exhibit Mie (surface plasmon) resonances unlike the case for Ag and Au, extremely prolate or oblate Cu nanoparticles with eccentricities near unity should give rise to Mie resonances in the lower end of the visible range and in the infra-red. This tunable resonance predicted by the classical Mie-Gans theory is reproduced with remarkable accuracy by our TDLDA computations on hypothetical Cu clusters in the form of zigzag chains with as few as 6 to 20 atoms.

Trends in the Reactivity of Molecular O2 with Copper Clusters: Influence of Size and Shape

“…In agreement with previous studies, [25][26][27][28][29] all methods indicate that planar (2D) isomers are the most stable up to n = 6, and three-dimensional (3D) structures are clearly preferred for clusters containing 7 or more atoms. For Cu 4, Cu 6 and Cu 7 clusters, the difference in energy between the two most stable isomers for each atomicity does not depend on the theoretical method used, with calculated relative energies differing by less than 1,5 kcal/mol.…”

“…[25][26][27][28][29] The reactivity of copper clusters, and its evolution with the number of atoms in the cluster, has been less investigated. The interaction of CO and O 2 with Cu n clusters with n ≤ 10 atoms and the dissociative chemisorption of H 2 on Cu n clusters of up to 15 atoms have been explored in detail, and a higher reactivity of copper clusters with an odd number of atoms has been reported with few exceptions.…”

Time-dependent density functional study of UV-visible absorption spectra of small noble metal clusters (Cun, Agn, Aun, n = 2–9, 20)

“…Recently, the optical absorption of small Cu n clusters embedded in neon matrix at 7 K have been measured 37 . Afterwards, TDDFT calculations using LDA 38 and B3LYP 37 density functionals were found to be not able to well reproduce the experimental data. Present work, with the use of long-range density functionals and an extended basis set, represents a significant improvement over previous theoretical studies since the d → sp interband transitions which may present a significant long-range charge-transfer character 9 will be better described.…”

Unraveling the electronic structure of transition metal dimers using resonant four‐wave mixing

“…The copper dimer has also proved troubling to theoreticians. Recent work on the absorption spectrum of Cu 2 has shown glaring deficiencies in the methods used, even for the low lying electronic states . Furthermore, the calculations have focused on Hund's case (a) coupling terms, whereas experiments have shown the need to consider the strong spin–orbit coupling that is present for the electronic states originating from the 2 S + 2 D separated atom limit.…”