  Bandgap engineering of low-dimensional materials forms a robust basis for
advancements in optoelectronic technologies. Platinum diselenide (PtSe2)
material exhibits a transition from semi-metal to semiconductor (SM-SC) when
going from bulk to monolayer (ML). In this work, density functional theory
(DFT) with various van der Waals (vdW) corrections has been tested to study the
effect of the layer-number on the structural and electronic properties of the
PtSe2 material. The considered vdW corrections gave different results regarding
the number of layers at which the SM-SC transition occurs. This variation is
due to the different interlayer distances found for each correction, revealing
the sensitivity of the bandgap to this distance in addition to the layer
number. In fact, the bandgap increases with the increasing of the interlayer
distance, due to the energy shift of conduction and valence bands dominated by
Se-pz orbitals. According to the comparison with the available experimental
data, the vdW corrections vdW-DF and rVV10 gave the most accurate results.
Moreover, the control of the interlayer distance via vertical compressive
strain led to the bandgap tuning of semiconductor PtSe2 BL. Indeed, a
semi-metal character of PtSe2 BL can be obtained under 17% vertical strain. Our
work shows a deep understanding of the correlation between the structural and
electronic properties, and thus a possibility to tune the bandgap by strain
means.
