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A charge–dipole interaction model for the frequency-dependent polarizability of silver clusters

A Mayer1,4, A L González2, C M Aikens3 and G C Schatz2

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We present a charge–dipole interaction model for the calculation of the frequency-dependent polarizability of silver clusters. The model relies on the representation of silver atoms by both a net electric charge and a dipole. Time variations of the atomic charges are related to the currents that flow through the bonds of the structures considered and the atomic charges and dipoles are eventually determined from the application of a least-action principle. After a generalization that enables the bonds of the bulk and surface atoms to have specific resistances, the model is parameterized on data obtained by the time-dependent density functional theory for tetrahedral Ag20, Ag84 and Ag120 clusters. We then study the polarization properties of dimers of silver clusters. We compare in particular the polarizability of the dimers with that of the isolated clusters, for a range of gap distances and frequencies. We also consider the field enhancements one can achieve with these systems. The results are in good agreement with reference data and enable an extension of these data to a wider range of situations. They show that significant field enhancements are achieved at frequencies associated with resonant polarization along the axis of the dimer.


PACS

36.40.Wa Charged clusters

36.40.Mr Spectroscopy and geometrical structure of clusters

31.15.E- Density-functional theory

32.10.Dk Electric and magnetic moments, polarizabilities

Subjects

Atomic and molecular physics

Computational physics

Dates

Issue 19 (13 May 2009)

Received 10 February 2009, in final form 17 March 2009

Published 20 April 2009



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