  Recently, a new two-dimensional carbon allotrope called pentagraphene (PG)
was proposed. PG exhibits mechanical and electronic interesting properties,
including typical band gap values of semiconducting materials. PG has a
Cairo-tiling-like 2D lattice of non coplanar pentagons and its mechanical
properties have not been yet fully investigated. In this work, we combined
density functional theory (DFT) calculations and reactive molecular dynamics
(MD) simulations to investigate the mechanical properties and fracture patterns
of PG membranes under tensile strain. We show that PG membranes can hold up to
20% of strain and that fracture occurs only after substantial dynamical bond
breaking and the formation of 7, 8 and 11 carbon rings and carbon chains. The
stress-strain behavior was observed to follow two regimes, one exhibiting
linear elasticity followed by a plastic one, involving carbon atom
re-hybridization with the formation of carbon rings and chains. Our results
also show that mechanically induced structural transitions from PG to graphene
is unlikely to occur, in contrast to what was previously speculated in the
literature.
