Accurate projected augmented wave datasets for BaFe$_2$As$_2$

TL;DR

This paper develops a high-quality PAW dataset for BaFe$_2$As$_2$, compares different exchange-correlation functionals, and investigates surface diffusion of Ba atoms, providing insights into electronic structure and surface properties.

Contribution

The authors created a new PAW dataset with improved parameters and semi-core orbitals, and applied it to study structural, electronic, and surface diffusion properties of BaFe$_2$As$_2$.

Findings

LDA fails to find the correct SDW-AFM ground state.

PBE overestimates magnetism but finds the correct state.

Ba atom diffusion barrier on the surface is 1.2 eV.

Abstract

By carefully choosing parameters and including more semi-core orbitals as valence electrons, we have constructed a high quality projected augmented wave (PAW) dataset that yields results comparable to existing full-potential linearized augmented plane-wave calculations. The dataset was then applied to BaFe$_2$As$_2$ to study the effects of different levels of structure optimization, as well as different choices of exchange-correlation functionals. It is found that the LDA exchange-correlation functional fails to find the correct SDW-AFM ground state under full optimization, while PBE exchange-correlation functional obtains the correct state but significantly overestimates the magnetism. The electronic structure of the SDW-AFM state is not very sensitive to structure optimizations with the PBE exchange-correlation functional because the position of the As atoms are preserved under optimizations. We further investigated the Ba atom diffusion process on the BaFe$_2$As$_2$ surface using the nudged elastic bands (NEB) method. The Ba atom was found to be stable above the center of the squares formed by the surface As atoms, and a diffusion barrier of 1.2 eV was found. Our simulated STM image suggests an ordered surface Ba atom structure, in agreement with Ref.