  We present a paradigm in constructing very stable, faceted nanotube and
fullerene structures by laterally joining nanoribbons or patches of different
planar phosphorene phases. Our ab initio density functional calculations
indicate that these phases may form very stable, non-planar joints. Unlike
fullerenes and nanotubes obtained by deforming a single-phase planar monolayer
at substantial energy penalty, we find faceted fullerenes and nanotubes to be
nearly as stable as the planar single-phase monolayers. The resulting rich
variety of polymorphs allows to tune the electronic properties of phosphorene
nanotubes (PNTs) and fullerenes not only by the chiral index, but also by the
combination of different phosphorene phases. In selected PNTs, a
metal-insulator transition may be induced by strain or changing the number of
walls.
