First Principle Local Density Approximation Description of the Electronic Properties of Ferroelectric Sodium Nitrite

The electronic structure of the ferroelectric crystal, NaNO$_2$, is studied by means of first-principles, local density calculations. Our ab-initio, non-relativistic calculations employed a local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). Following the Bagayoko, Zhao, Williams, method, as enhanced by Ekuma, and Franklin (BZW-EF), we solved self-consistently both the Kohn-Sham equation and the equation giving the ground state charge density in terms of the wave functions of the occupied states. We found an indirect band gap of 2.83 eV, from W to R. Our calculated direct gaps are 2.90, 2.98, 3.02, 3.22, and 3.51 eV at R, W, X, {\Gamma}, and T, respectively. The band structure and density of states show high localization, typical of a molecular solid. The partial density of states shows that the valence bands are formed only by complex anionic states. These results are in excellent agreement with experiment. So are the calculated densities of states. Our calculated electron effective masses of 1.18, 0.63, and 0.73 mo in the {\Gamma}-X, {\Gamma}-R, and {\Gamma}-W directions, respectively, show the highly anisotropic nature of this material.Comment: 13 Pages, 4 Figures, and 2 Table

Electronic structure and spectra of CuO

We report the electronic structure of monoclinic CuO as obtained from first principles calculations\ud utilizing density functional theory plus effective Coulomb interaction (DFT + U) method. In\ud contrast to standard DFT calculations taking into account electronic correlations in DFT + U gave antiferromagnetic\ud insulator with energy gap and magnetic moment values in good agreement with experimental\ud data. The electronic states around the Fermi level are formed by partially filled Cu 3dx2−y2 orbitals with\ud significant admixture of O 2p states. Theoretical spectra are calculated using DFT + U electronic structure\ud method and their comparison with experimental photoemission and optical spectra show very good\ud agreement.National Science Foundation award n. EPS-1003897Russian Foundation for Basic Research - projects n. 13-02-00050 e 12-02-91371-CTaRussian Federation - NSH-6172-2012.2Program of the Russian Academy of Science Presidium "Quantum microphysics of condensed matter" 12-P-2-1017Ministry of Education and Science of Russia n. 14.A18.21.0076Louisiana Optical Network Initiative (LONI)HPC@LSU computing resourcesGovernment of Ebonyi State, Nigeri

Theoretical and experimental investigations of optical, structural and electronic properties of the lower-dimensional hybrid [NH3-(CH2)10-NH3]ZnCl4

In the current study, a combination between theoretical and experimental studies has been made for the hybrid perovskite [NH3-(CH2)10-NH3]ZnCl4. The density functional theory (DFT) was performed to investigate structural and electronic properties of the tilted compound. A local approximation (LDA) and semi-local approach (GGA) were employed. The results are obtained using, respectively, the local exchange correlation functional of Perdew-Wang 92 (PW92) and semi local functional of Perdew-Burke-Ernzerhof (PBE). The optimized cell parameters are in good agreement with the experimental results. Electronic properties have been studied through the calculation of band structures and density of state (DOS), while structural properties are investigated by geometry optimization of the cell. Fritz-Haber-Institute (FHI) pseudopotentials were employed to perform all calculations. The optical diffuse reflectance spectra was mesured and applied to deduce the refractive index (n), the extinction coefficient (k), the absorption coefficient (α), the real and imaginary dielectric permittivity parts (εr,εi)) and the optical band gap energy Eg. The optical band gap energy value shows good consistent with that obtained from DFT calculations and reveals the insulating behavior of the material