Plasmon response and electron dynamics in charged metallic nanoparticles

Using the time-dependent density functional theory, we perform quantum calculations of the electron dynamics in small charged metallic nanoparticles (clusters) of spherical geometry. We show that the excess charge is accumulated at the surface of the nanoparticle within a narrow layer given by the typical screening distance of the electronic system. As a consequence, for nanoparticles in vacuum, the dipolar plasmon mode displays only a small frequency shift upon charging. We obtain a blue shift for positively charged clusters and a red shift for negatively charged clusters, consistent with the change of the electron spill-out from the nanoparticle boundaries. For negatively charged clusters, the Fermi level is eventually promoted above the vacuum level leading to the decay of the excess charge via resonant electron transfer into the continuum. We show that, depending on the charge, the process of electron loss can be very fast, on the femtosecond time scale. Our results are of great relevance to correctly interpret the optical response of the nanoparticles obtained in electrochemistry, and demonstrate that the measured shift of the plasmon resonances upon charging of nanoparticles cannot be explained without account for the surface chemistry and the dielectric environment.M.Z. acknowledges financial support from the Departamento Administrativo de Ciencia, Tecnologia e Innovacion-COLCIENCIAS and Facultad de Ciencias from Universidad de los Andes. M.Z. also gratefully acknowledges the hospitality of the Donostia International Physics Center and the Materials Physics Center in San Sebastian. J.A. acknowledges support from the Spanish Ministry of Economy and Competitiveness through project FIS2013-41184-P and project 2015CD0010 of the CSIC scientific cooperation program for development “ICOOP LIGHT” 2015.Peer reviewe