Combining the first-principles density functional method and crystal structure prediction techniques, we report a series of hexagonal two-dimensional transition metal borides including Sc ₂ B ₂ , Ti ₂ B ₂ , V ₂ B ₂ , Cr ₂ B ₂ , Y ₂ B ₂ , Zr ₂ B ₂ , and Mo ₂ B ₂ .

Monolayer SnP₃ is a novel two-dimensional (2D) semiconductor material with high carrier mobility and large optical absorption coefficient, implying its potential applications in the photovoltaic and thermoelectric (TE) fields.

Through first-principles calculations, we report on the phonon-limited transport properties of two-dimensional (2D) hexagonal MSe (M = Ge, Sn, and Pb) compounds, which can be seen as a new family of 2D group-IV selenides established by the isovalent substitutions of germanium and tellurium in layered ${\mathrm{Ge}}_4{\mathrm{Se}}_3\mathrm{Te}$ phase [ Angew. Chem. Inter. Edit. 56 10204 (2017)]. We find that 2D PbSe exhibits low values of sound velocity (800–2030 m/s), large $\mathrm{Gr}\ddot{\mathrm{u}}\mathrm{neisen}$ parameters $\left(\sim 1.93\right)$, low-lying optical modes $\left(\sim 20.02{\mathrm{cm}}^{-1}\right)$, and strong optical-acoustic phonon coupling. These intrinsic properties mainly stem from strong phonon anharmonicity, which greatly suppress the phonon transport and therefore give rise to an ultralow thermal conductivity $\left(\sim 0.26\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}\right)$ for 2D PbSe at room temperature. Our studies may offer perspectives for applications of thermoelectricity and motivate further experimental efforts to synthesize MSe compounds.

In this study, we report two new Mo₂B₂ monolayers and investigate their stabilities, electronic structures, lattice dynamics, and properties as anode materials for energy storage by using the crystal structure prediction technique and first-principles method.