Anisotropic dielectric function response of Ag-Au alloys evaluated via DFT

The accurate analysis of the optical and electronic properties of noble metals alloys is crucial to develop more efficient devices applied to optoelectronics and medical fields. Particularly, the use of first-principle calculations of silver (Ag) and gold (Au) nanoparticles (NPs) showed that they are promising candidates for the treatment of COVID-19. In this work, we calculate the band structure, the density of states, and the dielectric function (DF) of three Ag-Au alloys and their pure counterparts through the Density Functional Theory (DFT). We show that isotropic responses of the dielectric function is obtained for all systems except for a Ag_0.5Au_0.5. To validate our results, we compare them with several ones obtained experimentally from the literature. For the Ag_0.5Au_0.5 system, we see an inconsistency in the dielectric function's reported values in terms of the intra- and interband transition. Those values fall into two categories, matching the ones found in the anisotropic results. The method developed here can be extended to other metallic systems providing an accurate description of their optical response.