Optical Absorption Study by Ab initio Downfolding Approach: Application to GaAs

TL;DR

This study develops an ab initio downfolding approach to accurately model electronic excitation spectra, successfully applied to GaAs, capturing experimental results and providing a reliable framework for electronic structure analysis.

Contribution

The paper introduces a three-stage ab initio downfolding scheme combining density functional theory, Wannier functions, and a low-energy solver to accurately reproduce excitation spectra.

Findings

Spectra of GaAs closely match experimental data.

The method effectively captures electronic excitations and ground state properties.

The approach offers a reliable framework for electronic structure calculations.

Abstract

We examine whether essence and quantitative aspects of electronic excitation spectra are correctly captured by an effective low-energy model constructed from an {\em ab initio} downfolding scheme. A global electronic structure is first calculated by {\em ab initio} density-functional calculations with the generalized gradient approximation. With the help of constrained density functional theory, the low-energy effective Hamiltonian for bands near the Fermi level is constructed by the downfolding procedure in the basis of maximally localized Wannier functions. The excited states of this low-energy effective Hamiltonian ascribed to an extended Hubbard model are calculated by using a low-energy solver. As the solver, we employ the Hartree-Fock approximation supplemented by the single-excitation configuration-interaction method considering electron-hole interactions. The present three-stage method is applied to GaAs, where eight bands are retained in the effective model after the downfolding. The resulting spectra well reproduce the experimental results, indicating that our downfolding scheme offers a satisfactory framework of the electronic structure calculation, particularly for the excitations and dynamics as well as for the ground state.