  Very recently, the two-dimensional (2D) form of MoSi2N4 has been successfully
fabricated [Hong et al., Sci. 369, 670 (2020)]. Motivated by theses recent
experimental results, herein we investigate the structural, mechanical,
thermal, electronic, optical and photocatalytic properties using hybrid density
functional theory (HSE06-DFT). Phonon band dispersion calculations reveal the
dynamical stability of MoSi2N4 monolayer structure. Furthermore, the mechanical
study confirms the stability of MoSi2N4 monolayer. As compared to the
corresponding value of graphene, we find the Youngs modulus decreases by 30%
while the Poissons ratio increases by 30%. In addition, its work function is
very similar to that of phosphorene and MoS2 monolayers. The electronic
structure investigation shows the MoSi2N4 monolayer is an indirect bandgap
semiconductor. We have determined the bandgap using the HSE06 (GGA) is 2.35
(1.79) eV, which is an overestimated (underestimated) value of the experimental
bandgap (1.99 eV). The thermoelectric study shows a good thermoelectric
performance of the MoSi2N4 monolayer with a figure of merit slightly larger
than unity at high temperatures. The optical analysis using the RPA method
constructed over HSE06 shows that the first absorption peak of the MoSi2N4
monolayer for in-plane polarization is located in the visible range of
spectrum, i.e. it is a promising candidate for advancing optoelectronic
nanodevices. The photocatalytic study indicates the MoSi2N4 monloayer can be a
promising photocatalyst for water splitting as well as and CO2 reduction. In
summary, the fascinating MoSi2N4 monloayer is a promising 2D material in many
applications due to its unique physical properties.
