  We have assessed mechanical bending as a powerful controlling tool for the
electronic structure and optical properties of phosphorene nanoribbons. We use
state-of-the-art density functional approximations in our work. The overall
performance of the recently developed meta-generalized gradient approximation
(meta-GGA) mTASK [Phys. Rev. Mater. \textbf{5}, 063803 (2021)] functional
establishes the method as a useful alternative to the screened hybrid HSE06 for
better band gaps of phosphorene nanoribbons. We present a detailed and novel
analysis to interpret the optical absorption of bent phosphorene nanoribbons
using the GW-Bethe-Salpeter approximation (GW-BSE). We demonstrate the
important role of the unoccupied in-gap state and conclude that this in-gap
state in armchair nanoribbons introduced by bending can significantly affect
the properties of low-energy excitons, and add some useful opportunities for
applications as optoelectronic devices.
