Impact of Co doping on electronic response, momentum densities and localisation of d electrons of TiO2: Compton profiles and first-principles calculations

Concentration-dependent Mulliken's charge reorganisation, energy bands, density of states (DOS) and Compton profiles (CPs) are computed for Ti1_xCoxO2 (x = 0.00, 0.05 and 0.10) using linear combination of atomic orbitals (LCAO) scheme. The extant LCAO calculations have been featured using the density functional theory (DFT) and hybridization of DFT with the Hartree-Fock theory. An analysis of allowed energy states and DOS confirms a wide band gap semiconducting behaviour of TiO2, which is narrowed in doped oxides due to the formation of 3d interstitial bands in the lower part of the conduction region. Based on the reconciliation of CPs derived using LCAO computations and the present experiment of Co-doped TiO2 using 100 mCi 241Am Compton spectrometer, the applicability of exchange and correlation potentials is monitored. Present analysis on experimental and theoretical momentum densities show that one can equally employ pure DFT approximations or hybrid nature of exchange and correlation potentials in Co-doped TiO2 environment to explain the electronic properties. How-ever, the B3LYP may be a better choice to compute band gap properties for optoelectronic devices. Further, the nature of bonding through equally normalized CPs (experiment) is in tune with the Mulliken population data. Present work on momentum densities, Mulliken population and localization of d states categorically depict an enhancement of ionic character in a peculiar sequence TiO2 -> Ti0.90Co0.10O2 -> Ti0.95Co0.05O2.