Unfolding optical transition weights of impurity materials for first-principles LCAO electronic structure calculations

Abstract

A method to analyze optical transitions is developed by combining the Kubo-Greenwood formula with the unfolding method to construct an unfolded electronic band structure with optical transition weights, which allows us to investigate how optical transitions are perturbed by imperfections such as impurity, vacancy, and structural distortions. Based on the Kubo-Greenwood formula, we first calculate frequency-dependent optical conductivity based on the first-principles electronic structure calculations using the linear combinations of atomic orbitals. Benefiting from the atomic orbital basis sets, the frequency-dependent optical conductivity can be traced back to their individual components before summations over all of k points and bands. As a result, optical transition weights of the material can be put on the unfolded electronic band structure to show contributions at different k points and bands. This method is especially useful to study the effects of broken symmetry in the optical transitions due to presence of impurities in the materials. As a demonstration, decomposed optical transition weights of a monolayer Si-doped graphene are shown in the electronic band structure.

Magneto-Optical Kerr effect in surface engineered 2D hexagonal boron nitride

“…As the conductivity and dielectric function can be calculated based on the Kubo-Greenwood formula in this work we did not take into account the electron-hole interaction which is causing excitonic effects. 43 We considered a sufficiently large vacuum pad of 20 Å for these periodic structures to avoid any interaction between adjacent layers and the atomic positions were optimized using a quasi-Newton algorithm, where the force acting on each atom was less than 10 −3 eV/Å. For this purpose, we placed oxygen atoms at an energetically minimum position in bridge cites and let all atoms in the supercell be fully relaxed in all directions.…”

Magneto-optical Kerr effect in surface engineered 2D hexagonal boron nitride

“…As the conductivity and dielectric function can be calculated based on the Kubo-Greenwood formula in this work we did not take into account the electron-hole interaction which is causing excitonic effects 48 . We considered a sufficiently large vacuum pad of 20 Å for these periodic structures to avoid any interaction between adjacent layers and the atomic positions were optimized using a quasi-Newton algorithm, where the force acting on each atom was less than eV/Å.…”