Optical spectra of 2D monolayers from time-dependent density functional theory

Area of Science:

• Computational materials science
• Quantum chemistry
• Condensed matter physics

Background:

• Accurately predicting optical spectra of 2D materials is challenging due to significant excitonic effects.
• Standard time-dependent density-functional theory (TDDFT) often struggles with these large excitonic effects in 2D systems.

Purpose of the Study:

• To evaluate the accuracy of a pure Kohn-Sham TDDFT framework for describing optical spectra of 2D materials.
• To explore a method that avoids external corrections like the GW approximation for the electronic band gap.

Main Methods:

• Adapted a previously developed approach for 3D systems to analyze 2D periodic systems.
• Leveraged the connection between the TDDFT exchange-correlation kernel and the derivative discontinuity in ground-state DFT.
• Employed a generalized polarization functional to capture excitonic effects.

Main Results:

• The adapted protocol provides a qualitatively accurate description of the optical spectrum for hexagonal boron nitride (h-BN).
• The method shows limitations in accurately reproducing the intensity of excitonic peaks for molybdenum disulfide (MoS2).

Conclusions:

• The pure Kohn-Sham TDDFT approach, incorporating derivative discontinuity and a generalized polarization functional, shows promise for 2D material optical spectra.
• Further refinements are necessary for quantitative accuracy, particularly for materials with strong excitonic interactions like MoS2.