DFT insights into bandgap engineering of lead-free LiMCl3 (M = Mg, Be) halide perovskites for optoelectronic device applications

Abstract

In this theoretical analysis, the pressure-dependent structural, electronic, mechanical, and optoelectronic properties of LiMCl₃ (M = Mg, Be) have been calculated using density functional theory within the framework of the GGA PBE and hybrid HSE06 functional. At ambient pressure, the calculated lattice parameters of LiMCl₃ match well with previously reported values, validating the accuracy of this study. Geometry optimization reveals that under increasing hydrostatic pressure, both the lattice parameters and the unit cell volume decrease. Additionally, the band structure exhibits notable phenomena over the pressure range from 0 to 100 GPa. For the LiMgCl₃ compound, the bandgap decreases from an indirect bandgap of 4 eV to a direct bandgap of 2.563 eV. Similarly, LiBeCl₃ shows an indirect bandgap that decreases from 2.388 eV to 0.096 eV over the pressure range from 0 to 100 GPa. The optical properties of LiMCl₃, including absorption coefficient, reflectivity, refractive index, dielectric function, and conductivity, have been calculated throughout the study under varying pressure conditions. The analysis reveals that the optical properties of LiMCl₃ (M = Be, Mg) enhance with increasing hydrostatic pressure, thereby rendering these materials more suitable for optoelectronic applications. To assess the stability of these compounds, elastic constants were analyzed, indicating that LiMCl₃ exhibits ductile and anisotropic characteristics under different pressure conditions. These investigated materials are suitable for use in optoelectronic devices due to their favorable physical properties under different pressure circumstances.

Keywords: Bandgap engineering; DFT; Hydrostatic pressure; Lead-free perovskite; Mechanical properties; Optical properties.

Fig. 1

Crystal structure of cubic (a) LiMgCl₃ and (b) LiBeCl₃.

Fig. 2

Pressure-induced variation of (a) lattice parameters, (b) unit cell volume of LiMCl₃, and variation on bond length of (c) LiMgCl₃ and (d) LiBeCl₃.

Fig. 3

Phonon dispersion of LiMCl₃ (M = Mg, Be) compounds for 0 GPa and 100 GPa pressure conditions.

Fig. 4

Band structures of LiMgCl₃ under different hydrostatic pressure with GGA-PBE exchange-correlation functional.

Fig. 5

Band structures of LiBeCl₃ under different hydrostatic pressures with GGA-PBE exchange-correlation functional.

Fig. 6

The total density of states (TDOS) of (a) LiMgCl₃ and (b) LiBeCl₃ compounds under hydrostatic pressures (0-100 GPa).

Fig. 7

The partial density of states (PDOS) of LiMgCl₃ under pressures (0-100 GPa).

Fig. 8

The partial density of states (PDOS) of LiBeCl₃ under pressures (0-100 GPa).

Fig. 9

Pressure-induced variation of Real part of DF: (a) LiMgCl₃, (b) LiBeCl₃ and Imaginary part of DF: (c) LiMgCl₃, (d) LiBeCl₃.

Fig. 10

Pressure-induced variation of Absorption coefficient: (a) LiMgCl₃, (b) LiBeCl₃ and Conductivity: (c) LiMgCl₃, (d) LiBeCl₃.

Fig. 11

Pressure-induced variation of Reflectivity: (a) LiMgCl₃, (b) LiBeCl₃ and Refractive index: (c) LiMgCl₃, (d) LiBeCl₃.

Fig. 12

(a) Pugh’s ratio and (b) Poisson ratio of LiMgCl₃ and LiBeCl₃ under pressures.

Fig. 13

3D anisotropic representation of (a) Young’s modulus, (b) shear modulus, and (c) Poisson’s ratio of LiMgCl₃ and LiBeCl₃ under 0 GPa and 100 GPa pressures.