Surface and Interface Energetics of Pyrite-type Materials*

Materials with the pyrite crystal structure, such as iron and cobalt sulfide, are composed of earth-abundant
elements with potential applications in photovoltaics, catalysis, and spintronics. While the surface
properties of FeS₂ have received significant attention in the literature, less is known about the surface
properties of other pyrite-type materials like CoS₂ as well as the interfaces between these materials. In this
work, we perform calculations using density functional theory (DFT) to gain insight into the surface and
interface energetics of these pyrite materials. Specifically, we compute the energies for several low-index
surface orientations with different surface terminations (i.e., sulfur-rich to sulfur-poor). We compare the
minimal surface energy and interface energy between the two materials along these directions. Extending
the basic surface characterization, we also include the effects of ligands bound to these surfaces. The
results provide insights concerning the observed epitaxy of these materials in hybrid nanoparticle
experiments and provide guidance for additional experiments regarding the growth of structures utilizing
these materials.