Surface properties of the clean and Au/Pd covered Fe$_3$O$_4$(111): a DFT and DFT+$U$ study

TL;DR

This study uses DFT and DFT+U calculations to explore the surface structure, stability, and metal adsorption properties of Fe3O4(111), revealing significant relaxations, stability of iron termination, and stronger Pd binding compared to Au.

Contribution

It provides a detailed comparison of surface relaxations, stability, and adsorption energies on Fe3O4(111) using both DFT and DFT+U methods, highlighting the effects of Hubbard U.

Findings

Fe3O4(111) surfaces exhibit large relaxations of interlayer distances.

Iron-terminated surface is most stable across various oxygen chemical potentials.

Pd binds more strongly than Au to the Fe3O4(111) surfaces.

Abstract

The spin-density functional theory (DFT) and DFT+$U$ with Hubbard $U$ term accounting for on-site Coulomb interactions were applied to investigate structure, stability, and electronic properties of different terminations of the Fe$_3$O$_4$(111) surface. All terminations of the ferrimagnetic Fe$_3$O$_4$(111) surface exhibit very large (up to 90%) relaxations of the first four interlayer distances, decreasing with the oxide layer depth. Our calculations predict the iron terminated surface to be most stable in a wide range of the accessible values of the oxygen chemical potential. The adsorption of Au and Pd on two stable Fe- and O-terminated surfaces is studied. Our results show that Pd binds stronger than Au both to the Fe- and O-terminated surface. DFT+$U$ gives stronger bonding than DFT. The bonding of both adsorbates to the O-terminated magnetite surface is by 1.5-2.5 eV stronger than to the Fe-terminated surface.