We analyze the changes in the electronic structures of single-layer and multilayer MoS 2 under pressure using first-principles methods including van der Waals interactions. For single-layer MoS 2 , the bond angle is found to control the electronic structure around the band gap under the pressure. For multilayer and bulk MoS 2 , the changes in electronic structure under pressure are mainly controlled by the coupling of layers. Under pressure, the band gap of single-layer MoS 2 changes from direct to indirect, while multilayer MoS 2 becomes a band metal. Analysis of the real-space distribution of band-decomposed charge density shows that this behavior can be understood in terms of the different Mo delectron orbitals making up the states near band gap including those at the top of valence band of Γ and K points and the bottom of conduction band along Λ and at the K point.
The optical absorption edge (E perpendicular to c) was measured on basal-plane samples of single-crystal W1-xMoxSe2(O<or=x<or=1) at temperatures of 15, 78 and 295K. The data were fitted to several expressions for the shape of the edge, with the best fit being to that expected for indirect allowed transitions. The phonon involved is in an optical branch, and its energy varies smoothly with x. The band-gap energy at any temperature varies smoothly with x, indicating that the band edges are the same for MoSe2, WSe2 and the compounds of intermediate compositions.
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