Student Colloquium: Kopinjol Baishya
“Ab Initio Studies of Optical Excitations in Noble Metal Clusters”
Abstract: In this talk, I will present the optical absorption spectra of clusters of Group IB elements, Ag and Cu, studied using ab-initio density functional theory and its time dependent generalization, TDDFT. Optical absorption spectra are calculated for the three lowest energy isomers of the Agn (n = 10, 12 – 20) clusters and the computed ground state structures for Cun (n = 2 – 20) clusters. The results are compared with available experimental data, existing calculations and our previous computations on gold clusters. The noble metals are interesting due to the presence of filled d-levels very close to a filled or half filled s-level giving rise to core-valence interactions which significantly modify their optical spectra. The effect of these d electrons, quenching the oscillator strengths and getting directly involved in low energy excitations; increase as we go from Ag to Cu to Au. Also 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.
Refreshments will be served at 2:30pm in 2214 SES