DFT and AIMD study of 2D Li2O2: Stability, electronic, magnetic, thermal, and optical properties

Abstract

We employ density functional theory to examine the structural, stability, electronic, magnetic, thermal, and optical properties of two atomic configurations of lithium peroxide with hexagonal lattice and decorated hexagonal lattice identifying as Li${}_2$O${}_2$-1 and Li${}_2$O${}_2$-2, respectively, within the $P{6}_3/mmc$ space group. Although part of the same crystallographic group, these two atomic configurations give rise to diverse physical properties. Examining the phonon band structure indicates that Li${}_2$O${}_2$-1 is dynamically unstable, whereas Li${}_2$O${}_2$-2 exhibits dynamic stability. The calculations of formation energy and ab-initio molecular dynamics simulations validate the energetic and thermal stability, respectively. Electronic structure computations using both GGA/PBE and HSE06 functional reveal that both structures are semiconductors, with Li${}_2$O${}_2$-2 displaying a broader band gap than Li${}_2$O${}_2$-1 due to less symmetry of Li${}_2$O${}_2$-2, and neither configuration exhibits magnetic ordering. Optical analyses indicate that both structures exhibit transparency in the visible spectrum with minimal optical conductivity. However, Li${}_2$O${}_2$-2 shows enhanced refractive indices and reflectivity in the ultraviolet range. Heat capacity trends indicate similar thermal characteristics, with Li${}_2$O${}_2$-2 demonstrating somewhat improved heat absorption at higher temperatures. The findings underscore the promise of both configurations, especially Li${}_2$O${}_2$-2, for energy storage and ultraviolet optoelectronic applications, providing significant insights for forthcoming investigations into two-dimensional materials.