  Recently, two-dimensional monolayer MoSi2N4 with hexagonal structure was
successfully synthesized in experiment (Hong et al 2020 Science 369, 670). The
fabricated monolayer MoSi2N4 is predicted to have excellent mechanical
properties. Motived by the experiment, we perform first-principles calculations
to investigate the mechanical properties of monolayer MoSi2N4, including its
ideal tensile strengths, critical strains, and failure mechanisms. Our results
demonstrate that monolayer MoSi2N4 can withstand stresses up to 51.6 and 49.2
GPa along zigzag and armchair directions, respectively. The corresponding
critical strains are 26.5% and 17.5%, respectively. For biaxial strain, the
ideal tensile strength is 50.6 GPa with a critical strain of 19.5%. Compared
with monolayer MoS2, monolayer MoSi2N4 possesses much higher elastic moduli and
ideal tensile strengths for both uniaxial and biaxial strains. Interestingly,
the critical strain and failure mechanism of zigzag direction in MoSi2N4 are
almost the same as those of armchair direction in MoS2, while the critical
strain and failure mechanism of armchair direction for MoSi2N4 are similar to
the ones of zigzag direction for MoS2. Our work reveals the remarkable
mechanical characteristics of monolayer MoSi2N4.
