Must Kohn-Sham Oscillator Strengths be Accurate at Threshold?

TL;DR

This paper investigates whether Kohn-Sham oscillator strengths are accurate at the photoabsorption threshold, revealing they are not, through detailed spectral analysis of helium atom models and experimental data.

Contribution

It demonstrates that Kohn-Sham oscillator strengths at the threshold can be inaccurate, providing a detailed spectral analysis and a highly accurate two-electron spectrum fit.

Findings

Kohn-Sham oscillator strengths are not necessarily accurate at the threshold.

A highly accurate fit of the two-electron spectrum near the threshold was developed.

The study compares theoretical Kohn-Sham spectra with experimental data.

Abstract

The exact ground-state Kohn-Sham(KS) potential for the helium atom is known from accurate wavefunction calculations of the ground-state density. The threshold for photoabsorption from this potential matches the physical system exactly. By carefully studying its absorption spectrum, we show the answer to the title question is no. To address this problem in detail, we generate a highly accurate simple fit of a two-electron spectrum near the threshold, and apply the method to both the experimental spectrum and that of the exact ground-state Kohn-Sham potential.