In band structures of PtSe2 - for k-path (K-G-M-K) ; for monolayer the valence band maximum (VBM) is fixed at Gamma point and while going to bilayer and higher layers, VBM shifts from Gamma point to between K-G point, even though conduction band maximum stays at same place (between G-M point). what is the reason behind this?
Dear Vishal Kumar Pathak ,
As far as I know there are two types of bandgaps, the direct bandgap materials where the maximum of the valence band aligns with the minimum of the condition condition. The transition on case of the direct bandgap does not require change of the momentum or the wave vector k.
In case of indirect bandgap there is k shift shift between the minimum of the conduction band and the maximum of the valence band.
For multi layers the arrangements will be three dimensional and the possible shift may change. This is a natural phenomena.
Best wishes
Dear Vishal,
The calculated energy band structure is strongly dependent on the crystal periodicity (remember the Bloch periodic functions). Therefore, the layered structures, which have low periodicity (or no periodicity at all , along the growth direction), will have different band structure from the bulk of 3D materials of the same material.
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