Electronic, optical and thermodynamic properties of ZnO monolayer under hydrostatic pressures: a first-principles study.

Abstract

CONTEXT: First-principles density functional theory (DFT) calculations were performed to investigate the electronic, optical, and thermodynamic properties of a ZnO monolayer under hydrostatic pressures ranging from 0 to 40 GPa. The values of bond lengths, energy band gap, and dielectric constant were deduced for the first time using the theoretical plasmon calculations, show good agreement with the computed and reported values. The structural stability of the ZnO monolayer was verified using binding energy and phonon dispersion calculations under both ambient and external pressures. The computed results reveal that the band gap decreases continuously from 1.647 eV at ambient pressure to 0 eV at 40 GPa, indicating a pressure-driven semiconductor to metal transition. The mechanical stability has been verified using elastic stiffness constants and the elastic properties were derived for 2D ZnO monolayer, are in good agreement with reported works. The calculated optical properties show the absorption edge undergoes red-shifts with pressure, primarily due to band gap narrowing, while the real part and refractive index increase as a result of enhanced electronic polarizability and lattice compression. A comparative analysis with graphene further demonstrates the high temperature dependence of thermodynamic properties of ZnO. These findings provide valuable insights into the tunable electronic, optical, and thermodynamic properties of ZnO monolayers, demonstrating their potential for deep ocean and aerospace applications. METHODS: The first-principles DFT calculations were performed using Cambridge Sequential Total Energy Package (CASTEP) code. These calculations were carried out within the generalized gradient approximation (GGA) parameterized by Perdew et al. scheme, along with the ultra-soft pseudo-potential reciprocal space representation. The structure was optimized using the Broyden, Fletcher, Goldfarb, and Shannon (BFGS) scheme. The integration over the Brillouin zone was performed using a plane wave basis set with a cut-off energy of 330.00 eV.

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