High thermal insulation and excellent thermal stability of ScCl3 monolayer: DFT study of electronic, phonon, magnetic, thermal, and optical properties

The structural, electronic, phonon, magnetic, thermal, and optical properties of the trihalide material scandium trichloride, ScCl${}_3$, in the form of 2D crystal structure is investigated via DFT studies. Ab-initio molecular dynamic, AIMD, simulations using NVT ensembles confirm excellent thermal stability of ScCl${}_3$. Our calculations reveal that the ScCl${}_3$ is a stable semiconductor structure with band gap of $3.93\mathrm{eV}$ (GGA) and $6.27\mathrm{eV}$ (HSE06) with ionic bonds. We find flat bands in ScCl${}_3$ around the Fermi energy. The band gap and band structure are the same for both spin up and down exhibiting a non-magnetic behavior due to the balanced spin configurations. The calculated modes of the phonon band structure indicate dynamical stability, and the high phonon density of states at low frequencies displays efficient absorption of thermal vibrations further contributing to the stability. Additionally, the increased entropy and heat capacity plateau shape at higher temperatures regimes suggest a transition towards a more disordered state while maintaining efficient thermal energy absorption. However, the low-frequency phonon group velocities imply rapid heat transfer within the material leading to a decrease in lattice thermal conductivity with increasing temperature. Thus, a very small lattice thermal conductivity is seen for an ScCl${}_3$ monolayer. Finally, the response of ScCl${}_3$ to ultraviolet light, characterized by variations in the refractive index and optical conductivity, suggests potential applications in optoelectronic devices.