First--principles calculation of the plasmon resonance and of the reflectance spectrum of Silver in the GW approximation

We show that the position and width of the plasmon resonance in Silver are correctly predicted by ab--initio calculations including self--energy effects within the GW approximation. Unlike in simple metals and semiconductors, quasiparticle corrections play a key role and are essential to obtain Electron Energy Loss in quantitative agreement with the experimental data. The sharp reflectance minimum at 3.92 eV, that cannot be reproduced within DFT--LDA, is also well described within GW.The present results solve two unsettled drawbacks of linear response calculations for Silver.