First-principles Investigation of the Dielectric Response of Gold-Silver Alloy

The alloys of gold and silver feature tunable dielectric response with excellent chemical stability and have broad applications in the area of plasmonics. The dielectric constants of such alloys are critical material parameters in the engineering of plasmonic structures and devices. A common practice to obtain the dielectric constants of alloys is to use the mole fraction average of the pure components. This method works in many materials but yields unsatisfactory results for gold-silver alloys. The nature of such discrepancy has yet to be understood. Here we present results from first-principles calculations of gold-silver alloys and unveil the atomistic-scale mechanism that dictates their dielectric response. The results not only elucidate the mystery in the gold-silver alloys but can also be used to guide the design of other metallic alloys for plasmonics applications.