DFT and AIMD study of stability, electronic, magnetic, thermal, and optical properties of two-dimensional ZnX2 (X = Cl, Br and I) semiconductor

This work examines the structural, electronic, magnetic, thermal, dynamic, and optical properties of two-dimensional (2D) ZnX${}_2$ (X = Cl, Br, I) through density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. The 2D ZnX${}_2$ exhibits planar buckling in which ZnI${}_2$ exhibits the highest degree of buckling, followed by ZnBr${}_2$ and ZnCl${}_2$. Consequently, the highest buckling of ZnI${}_2$ exhibits the narrowest band gap, while the lowest buckling structure of ZnCl${}_2$ gives rise a widest band gap. This suggests that the electronic band gap is predominantly influenced by buckling in addition to electronegativity differences. Moreover, spin–orbit coupling (SOC) induces a reduction in the band gaps of these non-magnetic structures, primarily through the splitting and shifting of electronic states. Furthermore, stability assessments confirm that ZnX${}_2$ structures are dynamically and thermally stable. In addition, thermal analysis reveals that ZnI${}_2$ has the highest heat capacity, attributed to degenerate acoustic phonons. Finally, optical investigations indicate ZnI${}_2$ absorbs light in the near-UV spectrum, while ZnCl${}_2$ and ZnBr${}_2$ absorb in the Mid-UV region. The planar buckling significantly influence the physical properties of ZnX${}_2$ enhancing their suitability for advanced technological applications.