Computational prediction and characterization of two-dimensional pentagonal arsenopyrite FeAsS

Abstract

Two-dimensional (2D) pentagonal materials emerge as a new group of 2D materials with pentagonal rather than the more common hexagonal structure. Most of the existing and predicted 2D pentagonal materials are binary compounds, whereas adding more elements is likely to bring in extra properties. We apply a datamining process in the Materials Project to search for 3D ternary compounds, where one can derive 2D materials with pentagonal structure. We identify 34 ternary compounds that exhibit negative formation energies. We focus on one of these compounds, FeAsS, and we find that its single-layer counterpart exhibits an almost completely planar structure with dynamically stable phonon modes. This single-layer material is also a semiconductor with the antiferromagnetic (AFM) ordering. We also find that the Fe-As-Fe and Fe-S-Fe exchange couplings are of antiferromagnetic and ferromagnetic types, respectively, and the former exchange coupling strength is significantly stronger, leading to the AFM ordering. Finally, we account for the spin-orbit coupling (SOC) in the computational characterization. We find strong magnetocrystalline anisotropy as a result of the SOC. We further compute the Berry curvature for single-layer pentagonal FeAsS and find that at the Y point of the reciprocal space, the Berry curvature is both sizable and asymmetric. We expect more theoretical efforts to be spent towards designing 2D ternary pentagonal materials as a result of this work.