  Edge atomic configuration often plays an important role in dictating the
properties of finite-sized two-dimensional (2D) materials. By performing ab
initio calculations, we identify a highly stable zigzag edge of phosphorene,
which is the most stable one among all the considered edges. Surprisingly, this
highly stable edge exhibits a novel nanotube-like structure, which is
topologically distinctively different from any previously reported edge
reconstruction. We further show that this new edge type can form easily, with
an energy barrier of only 0.234 eV. It may be the dominant edge type at room
temperature in vacuum condition or even under low hydrogen gas pressure. The
calculated band structure reveals that the reconstructed edge possesses a
bandgap of 1.23 eV. It is expected that this newly found edge structure may
stimulate more studies in uncovering other novel edge types and further
exploring their practical applications.
