The density functional theory (DFT) calculations were performed using the Projected Augmented Wave (PAW) method to solve the Kohn-Shan equations as implemented in the Vienna Ab initio Simulation Package (VASP). The spin-polarized generalized gradient approximation has been used with the Perdew, Burke, and Ernzerhof (PBE) parametrization to describe the exchange and correlation term of the Kohn-Sham Hamiltonian. Moreover, the DFT+D3 approach was used to take into account the van der Waals interactions. Since methanol has been used as a solvent in the chemical treatment protocol, the starting point here is to check whether methanol would influence the passivation of these defects or coverage of the WS2 monolayers. Calculations of adsorption energies of methanol vs. 2furanmethanothiol (FSH) molecule considered a defect-free 2D surface, 2D surface with a neutral sulfur vacancy (SV) defect, and a negatively charged sulfur vacancy defect, since these two are the most common SV types in 2D WS2 layers. The results have shown that the adsorption of FSH molecule ends with a negative adsorption energy (exothermic reaction as has been defined) only on the non-defective WS2 layer while methanol does not adsorb on the layers in any considered case (Table ). The stronger probability of finding FSH on the nondefective surface of the layers is a result of the wan-der-walls interaction between this molecule and the 2D WS2 layer. This probability is much lower for the case of methanol. Though it is likely that thiol physisorbs and cover the 2D layer, such weak interaction does not change the electronic structure of the layer as shown in Figure and S18, which cannot explain the observed PL enhancement after the chemical treatment.