  Based on ab initio evolutionary crystal structure search computation, we
report a new phase of phosphorus called green phosphorus ({\lambda}-P), which
exhibits the direct band gaps ranging from 0.7 to 2.4 eV and the strong
anisotropy in optical and transport properties. Free energy calculations show
that a single-layer form, termed green phosphorene, is energetically more
stable than blue phosphorene and a phase transition from black to green
phosphorene can occur at temperatures above 87 K. Due to its buckled structure,
green phosphorene can be synthesized on corrugated metal surfaces rather than
clean surfaces.
