  We study the effects of the uniaxial tensile strain and shear deformation as
well as their combinations on the electronic properties of single-layer black
phosphorene. The evolutions of the strain-dependent band gap are obtained using
the numerical calculations within the tight-binding (TB) model as well as the
first-principles (DFT) simulations and compared with previous findings. The
TB-model-based findings show that the band gap of the strain-free phosphorene
agrees with the experimental value and linearly depends on both stretching and
shearing: increases (decreases) as the stretching increases (decreases),
whereas gradually decreases with increasing the shear. A linear dependence is
less or more similar as compared to that obtained from the ab initio
simulations for shear strain, however disagrees with a non-monotonic behaviour
from the DFT-based calculations for tensile strain. Possible reasons for the
discrepancy are discussed. In case of a combined deformation, when both strain
types (tensile/compression + shear) are loaded simultaneously, their mutual
influence extends the realizable band gap range: from zero up to the values
respective to the wide-band-gap semiconductors. At a switched-on combined
strain, the semiconductor-semimetal phase transition in the phosphorene is
reachable at a weaker (strictly non-destructive) strain, which contributes to
progress in fundamental and breakthroughs.
