  Using molecular dynamics (MD) simulations, we explore the structural
stability and mechanical integrity of phosphorene nanotubes (PNTs), where the
intrinsic strain in the tubular PNT structure plays an important role. It is
proposed that the atomic structure of larger-diameter armchair PNTs (armPNTs)
can remain stable at higher temperature, but the high intrinsic strain in the
hoop direction renders zigzag PNTs (zigPNTs) less favorable. The mechanical
properties of PNTs, including the Young's modulus and fracture strength, are
sensitive to the diameter, showing a size dependence. A simple model is
proposed to express the Young's modulus as a function of the intrinsic axial
strain which in turns depends on the diameter of PNTs. In addition, the
compressive buckling of armPNTs is length-dependent, whose instability modes
transit from column buckling to shell buckling are observed as the ratio of
diameter/length increases.
