Very recently, the 2D form of MoSi ₂ N ₄ has been successfully fabricated (Hong et al 2020 Science 369 670). Motivated by these recent experimental results, we investigate the structural, mechanical, thermal, electronic and optical properties of the MoSi ₂ N ₄ monolayer. The mechanical study confirms the stability of the MoSi ₂ N ₄ monolayer. The Young’s modulus decreases by ∼30%, while the Poisson’s ratio increases by ∼30% compared to the corresponding values of graphene. In addition, the MoSi ₂ N ₄ monolayer’s work function is very similar to that of phosphorene and MoS ₂ monolayers. The electronic structure shows that the MoSi ₂ N ₄ monolayer is an indirect semiconductor with a band gaps of 1.79 (2.35) eV using the GGA (HSE06) functional. The thermoelectric performance of the MoSi ₂ N ₄ monolayer has been revealed and a figure of merit slightly larger than unity at high temperatures is calculated. The optical analysis shows that the first absorption peak for in-plane polarization is located in the visible range of the spectrum, therefore, the MoSi ₂ N ₄ monolayer is a promising candidate for advanced optoelectronic nanodevices. In summary, the fascinating MoSi ₂ N ₄ monoloayer is a promising 2D material for many applications due to its unique physical properties.

Very recently, a new class of the multicationic and -anionic entropy-stabilized chalcogenide alloys based on the (Ge, Sn, Pb) (S, Se, Te) formula has been successfully fabricated and characterized experimentally [Zihao Deng et al., Chem. Mater. 32, 6070 (2020)]. Motivated by the recent experiment, herein, we perform density functional theory-based first-principles calculations in order to investigate the structural, mechanical, electronic, optical, and thermoelectric properties. The calculations of the cohesive energy and elasticity parameters indicate that the alloy is stable. Also, the mechanical study shows that the alloy has a brittle nature. The GeSnPbSSeTe alloy is a semiconductor with a direct band gap of 0.4 eV (0.3 eV using spin–orbit coupling effect). The optical analysis illustrates that the first peak of Im(ε) for the GeSnPbSSeTe alloy along all polarization directions is located in the visible range of the spectrum which renders it a promising material for applications in optical and electronic devices. Interestingly, we find an optically anisotropic character of this system which is highly desirable for the design of polarization-sensitive photodetectors. We have accurately predicted the thermoelectric coefficients and have calculated a large power factor value of 3.7 × 10¹¹ W m^–1 K^–2 s^–1 for p-type. The high p-type power factor is originated from the multiple valleys near the valence band maxima. The anisotropic results of the optical and transport properties are related to the specific tetragonal alloy unit cell.