Van der Waals Density Functional Theory Study of Molecular Adsorbates on MoX2(X = S, Se or Te)

We have investigated binding properties between molecular adsorbates and transition metal dichalcogenide (TMD) such as MoS2, MoSe2, and MoTe2 using density functional theory (DFT) calculations with various van der Waals (vdW) functionals. It is found that calculated lattice parameters of MoX2 (X = S, Se, or Te) obtained by the vdW functionals give the relative errors of up to +/- 5% with respect to the experimental values. Depending on the binding behaviors of molecular adsorbates on MoX2 surface, the vdW functionals can be classified into three group; (1) DFT-D2, DFT-D3, DFT-D3(BJ), DFT-TS, and optB86b-vdW, (2) DFT-TS-SCS, and (3) optB88- vdW, optPBE-vdW, revPBE-vdW, and rPW86-vdW2 functionals. Moreover, we find that the optPBE-vdW functionals show relatively large binding energies, while DFT-TS-SCS functionals show relatively small binding energies between molecular adsorbates and MoX2.