Computational characterization of optical response in noble metals and plasmonic ceramics

Understanding the optical response of plasmonic materials is essential for understanding the physics and functionality of plasmonic devices. While traditional plasmonic materials such as noble metals have shown great success, the search of alternative materials for high-temperature applications remains open in the community. In recent years, several transition-metal nitrides and carbides have emerged as a promising new family of plasmonic materials. Benefiting from their high thermal stability, these materials are expected to be promising for easy processing and for high-temperature applications. To better understand and guide the discovery of new plasmonic materials, a reliable computational first-principles framework to characterize optical properties of metallic systems is important. These characterizations require a predictive treatment of free-carrier absorption considering both inter- and intra-band single particle excitation, and the collective oscillation of electrons (Drude contribution) on the same footing.<br/><br/>In this work, we present a computational framework that combines density functional theory, density functional perturbation theory, many-body perturbation theory, the maximally localized Wannier function approach, and the special displacement method to capture the direct and phonon-assisted single-particle process, as well as the Drude contribution, to provide a consistent, predictive description of the optical response of metallic systems. We show that with our framework, we can characterize the optical response both of noble metals (Ag, Au, and Cu) and of TiN, a promising plasmonic ceramic material. We achieve excellent agreement with experimentally measured dielectric functions, and we successfully characterize the temperature dependence of the optical response of TiN. We show that in the IR to visible region, both single-particle phonon-assisted indirect transitions and the Drude contribution are important to understand optical response of metals. Our framework is general and is available as a community tool implemented in the open source EPW code. It can be extended to other metallic materials, thus provides a general platform to accurately model the optical properties of metallic materials. Our platform creates an excellent opportunity to enable rational design of new plasmonic materials for nonconventional applications.<br/><br/>This work was supported as part of the Computational Materials Sciences Program funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award No. DE-SC0020129. It used resources of the National Energy Research Scientific Computing (NERSC) Center, a DOE Office of Science User Facility supported under Contract No. DE-AC02–05CH11231.