Strong charge and spin fluctuations in La$_2$O$_3$Fe$_2$Se$_2$

TL;DR

This study compares DFT+U and DFT+G methods to analyze La$_2$O$_3$Fe$_2$Se$_2$, revealing that charge and spin fluctuations significantly influence its electronic and magnetic properties, with DFT+G aligning better with experimental data.

Contribution

The paper demonstrates that DFT+G captures charge and spin fluctuations in La$_2$O$_3$Fe$_2$Se$_2$, providing more accurate electronic structure predictions than DFT+U.

Findings

DFT+U overestimates the band gap.

DFT+G yields a band gap consistent with experiments.

Charge and spin fluctuations are crucial for accurate modeling.

Abstract

The electronic structure and magnetic properties of the strongly correlated material La$_2$O$_3$Fe$_2$Se$_2$ are studied by using both the density function theory plus $U$ (DFT+$U$) method and the DFT plus Gutzwiller (DFT+G) variational method. The ground-state magnetic structure of this material obtained with DFT+$U$ is consistent with recent experiments, but its band gap is significantly overestimated by DFT+$U$, even with a small Hubbard $U$ value. In contrast, the DFT+G method yields a band gap of 0.1 - 0.2 eV, in excellent agreement with experiment. Detailed analysis shows that the electronic and magnetic properties of of La$_2$O$_3$Fe$_2$Se$_2$ are strongly affected by charge and spin fluctuations which are missing in the DFT+$U$ method.