Comparative ab initio study of the structural, electronic, dynamical, and optical properties of group-I based CuMO2 (M = H, Li, Na, K, Rb)

Despite similar chemical compositions, the CuMO2 (M = H, Li, Na, K, Rb) compounds show remarkably distinct structural, electronic, dynamical, and optical properties. Different alkali atoms have a significant influence on their electronic, dynamical, and optical behavior. By means of first principles based density functional theory calculations, we explore the universality of electronic characteristics, dynamical stability, and optical properties of these compounds. The electronic band structures, vibrational frequencies, and optical properties are deeply connected with the atomic radius of the alkali atoms. The electronic bandgap of CuMO2 (M = H, Li, Na, K, Rb) lies within the range of 0.5–1.0 eV bringing them in the group of low bandgap p-type semiconductors. We found a significant increase in the bandgap and p–d hybridization as going from H to Rb. Partial density of states revealed strong metal–oxygen (Cu–O) overlap due to the strong p–d hybridization. The phonon dispersion curves obtained for these compounds confirm the dynamical stability as there is no imaginary frequency throughout the Brillouin zone. The static dielectric constants and refractive index fall within the range of 8.0–12.91 and 1.98–3.55, respectively, suggesting the usefulness of scrutinized compounds in non-linear optical devices. The optical properties depict that the alkali atoms based delafossites can serve as promising candidates for highly efficient optical devices within a broad range from visible to ultraviolet light of electromagnetic spectra.