Spin-Orbit Coupling Effects on the Structural and Electronic Properties of Planar Pentagonal p-MS${}_2$ (M = Si, Ge, and Pb)

Abstract

Spin-orbit coupling (SOC) plays an important role in determining the structural and electronic properties of recently proposed two-dimensional planar pentagonal materials. In this work, density functional theory calculations are employed to investigate SOC effects in p-MS${}_2$ systems (M = Si, Ge, and Pb). Our results indicate that the p-SiS${}_2$ structure is likely unstable, except for p-GeS${}_2$ and p-PbS${}_2$. A detailed j-resolved (total angular momentum) orbital analysis reveals that SOC enhances electronic localization, leading to a slight structural contraction and a reconstruction of electronic states near the Fermi level, this effect becoming stronger for heavier M atoms. While p-GeS${}_2$ remains metallic, SOC drives a metal-semiconductor transition in p-PbS${}_2$ and opening a quasi-direct band gap of about 0.475 eV. In addition, the conduction band minimum state of p-PbS${}_2$ exhibits pronounced anisotropy along the S-S bonds. These findings provide insight into SOC-driven structural and electronic reconstruction in planar pentagonal chalcogenides p-MS${}_2$ and suggest that p-PbS${}_2$ may be a promising candidate for gas-sensing applications.