Quasi-Molecular Perspective on the Planarity of 2D Materials: The case of 2D MoS2

Abstract

The geometry of two-dimensional (2D) materials is explored, with a focus on monolayer MoS2 , through the lens of a quasi-molecular framework. In this approach, the extended 2D sheet is interpreted as a tiling of structural "tiles" -such as small molecular fragment units fully optimized at a high level of quantum chemical theory. This model provides a cost-effective and physically intuitive means of analyzing planarity and local bonding in large multi-layer systems. Specifically, we assess whether quasi-planar tiles can account for the observed planarity of 2D MoS 2 , a material well-known for its S-Mo-S trilayer structure and trigonal prismatic coordination. By studying optimized Mo n S 2n clusters (n = 1 -12), we show that even though full planarity is not strictly preserved, a quasi-planar character emerges consistently. The results offer a compelling molecular perspective on extended materials and suggest that quasi-molecular tiling can effectively capture the local geometry and electronic structure of 2D MoS 2 .