Molybdenum disulfide monolayer electronic structure information as explored using density functional theory and quantum theory of atoms in molecules

Abstract

We use density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) to study the electronic structure of pristine and defect molybdenum disulfide (MoS2) monolayers, at dry and hydrated conditions. We study various defect MoS2 configurations, which are described by the presence of one or more sulfur (S) vacancies, including voids. Structural defects introduce deep and shallow defect states in the electronic band structure in the vicinity of the Fermi energy, which affect the bandgap and introduce mid-gap states. Hydration also affects the bandgap and the mid-gaps of defect MoS2. We use QTAIM parameters at bond critical points to identify the MoS2 bond types and their strength. QTAIM shows the presence of MoS and SS bonding, the former being weakly covalent, and the latter refers to a closed shell interaction. Water and its dissociated products are strongly adsorbed on Mo atoms due to the presence of low electron density areas in the vicinity of these atoms. We finally provide a correlation between changes in the electron density at the Mo-S bond critical points around the structural defect and the mid-gap around the Fermi energy. These findings become relevant for designing electrocatalysts based on MoS2 and two-dimensional layered systems.