On the mere exigency of exchange potential in ab initio calculations of nanocobalt ferrites: Compton spectroscopy and band structure calculations

Compton profiles (CPs) of nano-Zn-doped Co1−xZnxFe2O4 (x = 0 and 0.5) are reported using 137Cs Compton spectrometer with an experimental resolution of 0.34 a.u. (Gaussian FWHM). To check the usefulness of exchange and correlation energies for such type of nanoferrites, the experimental CPs have been compared with the Compton lines deduced using linear combination of atomic orbitals (LCAO) with Hartree–Fock (HF) scheme and range separated hybrid functionals, namely HISS and HSE06, and also a simple HF free atom model. Among the considered approximations, namely free atom and LCAO-based calculations, theoretical CPs based on LCAO-HF approximation reconcile better agreement with the measured momentum densities which unambiguously establish avoidance of correlation potentials in case of nanophase of the ferrites. It is seen that the quantum confinement effect (which is responsible for spatial enclosure of electronic charge carriers within the nanoscale) leads to discrete electronic energy states and optical transitions. Accordingly, the absorption of electromagnetic radiations can be chosen throughout the ultraviolet, visible, near-infrared and mid-infrared optical ranges. Significant changes in spin-projected energy bands (depicting discrete energy levels) and optical properties of nanoferrites in comparison with bulk ferrites unambiguously show remarkable amendments in electronic and optical properties of the studied nanoferrites.