Density functional study of twisted graphene $L1_0$-FePd heterogeneous interface

Graphene on $L1_0$-FePd(001), which has been experimentally studied in recent years, is a heterogeneous interface with a significant lattice symmetry mismatch between the honeycomb structure of graphene and tetragonal alloy surface. In this work, we report on the density functional study of its atomic-scale configurations, electronic and magnetic properties, and adsorption mechanism, which have not been well understood in previous experimental studies. We propose various atomic-scale models, including simple nontwisted and low-strain twisted interfaces, and analyze their energetical stability by performing structural optimizations using the van der Waals interactions of both DFT-D2 and optB86b-vdW functionals. The binding energy of the most stable structure reached $E_\mathrm{B}=-0.22$~eV/atom for DFT-D2 ($E_\mathrm{B}=-0.19$~eV/atom for optB86b-vdW). The calculated FePd-graphene spacing distance was approximately 2~\AA, which successfully reproduced the experimental value. We also find out characteristic behaviors: the modulation of $\pi$-bands, the suppression of the site-dependence of adsorption energy, and the rise of \color{blue} moir\'e-like \color{black} corrugated buckling. In addition, our atomic structure is expected to help build low-cost computational models for investigating the physical properties of $L1_0$ alloys/two-dimensional interfaces.