Real-time time-dependent density functional theory for the dielectric function of plasmonic materials

Abstract

To increase the data storage density of current hard drives Seagate Technology uses heat-assisted magnetic recording (HAMR). HAMR relies on a localised surface plasmon (LSP) to heat a nanometer-sized spot (diameter 50 nm) on the hard-drive platter. HAMR technology requires a plasmonic material which can sustain a high-quality LSP while operating in high-temperature environments for the lifetime of the hard drive. To assist in the search for plasmonic materials, first principle calculations can be used to predict the plasmonic properties of a candidate material which can then inform device fabrication. We seek a first principle calculation that can accurately predict the plasmonic properties at minimal computational expense. This research uses the real-space real-time time-dependent density functional theory(TDDFT) to calculate the dielectric function and estimate the plasmonic properties of metals. We use DFT+U to improve upon local and semi-local functionals which tend to underestimate onset of the interband transitions. DFT+U is less computationally expensive than hybrid functionals and the GW method. While DFT+U can be applied empirically by tuning the Hubbard U to align with an experimental observable, we apply the fully ab initio approach, the ACBN0functional. The ACBN0 functional is found to overestimate the interband onset which suggested the introduction of the short-range ACBN0 functional. The dielectric function calculated using the short-range ACBN0 functional is in good agreement with both empirical DFT+U and experiments for copper, silver and gold. The short range-ACBN0 functional is shown to reduce to the local density approximation (LDA) in titanium nitride, as LDA is a good approximation for titanium nitride. The protocol presented for calculating the dielectric function accurately predicts the plasmonic properties and is computationally inexpensive, with potential applications in material discovery for plasmonic devices.

Thesis embargoed until 31 December 2025.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Engineering and Physical Sciences Research Council
Supervisor	Lorenzo Stella (Supervisor) & Myrta Grüning (Supervisor)