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Abstract:
In the framework of density functional theory, the geometry, electronic
structure, and magnetic properties of the bulk and low index surfaces of
MoSe2 have been studied. We have carried out calculations with various
exchange-correlation functionals to select one which is able to describe
the van der Waals (vdW) interactions and gives the best geometry
compared with experiments. The inclusion of the vdW forces, however,
does not guarantee a reliable description for the geometry of this
compound: some vdW functionals strongly overestimate the interlayer
distance, similar to GGA functionals. Our investigation shows that the
recently introduced optB86b-vdW functional yields the best results for
MoSe2. The vdW functionals have less impact on the electronic structure:
the differences between the band structures of the experimental atomic
structure, calculated by the vdW-DF and PBE functionals are marginal. We
have tried the HSE06 hybrid functional as well but the results are not
satisfactory: the overestimated interlayer distance leads to a
significant overestimation of the band gap. The band structure of the
bulk and monolayer is calculated and by the analysis of the bands
character the indirect to direct band-gap transition is explained. The
surface energy, work function and band structure of the surfaces are
calculated as well. The role of the MoSe2 buffer layer in Cu(In,Ga) Se-2
based solar cells is discussed by considering the work function values.
