Electronic structure and dispersion of optical function of tantalum nitride as a visible light photo-catalyst

Tantalum nitride Ta3N5, as a visible light photocatalyst is studied using the state-of-the-art full potential linear augmented plane wave (FPLAPW) method in a scalar relativistic version. The calculated energy band gap values are vary between 1.1 eV (LDA), 1.2 eV (GGA), 1.5 eV (EVGGA) and 2.1 eV (mBJ). The band gap obtained using mBJ show excellent agreement with the experimental value 2.1 eV than the previous calculation. Thus mBJ potential is applied to investigate the ground state properties of tantalum nitride. The conduction band minimum is located at Y point of BZ, while the valence band maximum is located at the center of BZ indicates that the tantalum nitride is an indirect band gap semiconductor. The calculated electron charge density contours show that covalent bond exist between Ta and N atoms. The optical properties are discussed in details to seek deeper insight for the electronic structure. The calculated uniaxial anisotropy of Ta3N5, indicate a strong anisotropy of the optical dielectric functions. The absorption spectrum show that the absorption occurs in the visible region which makes Ta3N5 as an active photocatalyst under visible light irradiation. Ta3N5 crystal almost behaves as transparent in the higher wavelength light.