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In this study, all-inorganic two-dimensional Dion–Jacobson halide perovskites (DJ-HPs) CsMX 2 Y 2 (M = Sb, Bi; and X/Y= I/I, I/Br, Br/Br, I/Cl, Br/Cl, Cl/Cl) have been studied for photovoltaic, photoemission and other potential applications in optoelectronic devices using first principle calculations within the framework of density functional theory (DFT). The ground state crystal symmetry is tetragonal with a P 4/ mmm (No. 123) space group. In these compounds, Cs+ is a spacer cation, which separates the octahedral layers and balances the charge. The corner sharing M-centered (Sb, Bi) [MX 2 Y 4 ]3– unit constructs the 2D [MX 2 Y 2 ] n n– plane, where the X and Y (halogens) atoms occupy the out of plane apical and in-plane bridging sites, respectively. The DJ-HPs with P 4/ mmm crystal symmetry exhibit pseudo-direct band gap semiconducting nature and the spin orbit (SO) effect reduces the band gaps as well as splits the Sb/Bi-p orbital in the bottom of conduction band (CB) and X/Y-p orbital at the top of valence band (VB). Among these DJ-HPs, the band gap energies of CsSbI 2 Cl 2 (0.87 eV), CsSbBr 2 Cl 2 (1.00 eV), CsSbCl 4 (1.40 eV), CsBiI 4 (1.10 eV), CsBiI 2 Br 2 (1.40 eV) and CsBiBr 4 (1.60 eV) lie in a band gap energy range (0.9–1.6 eV) suitable for photovoltaic applications. The M-s (Sb-5s and Bi-6s) and X/Y-p (Cl-3p, Br-4p and I-5p) orbitals are responsible for the electron transition from the valence to conduction band, while the spacer cation (Cs+) has a limited effect on the charge carrier mobility. The effective masses of the charge carriers and exciton binding energies of these materials are suitable for solar cell and optoelectronic applications. From the optical coefficients it is clear that these DJ-HPs have excellent response to the incident photons in the visible and ultraviolet light region. • New Dion–Jacobson two dimensional halide are investigated for optoelectronic applications. • These compounds belongs to tetragonal symmetry having space group P 4/ mmm. • Band gap of these semiconductors are pseudo direct and spin orbit (SO) effect increases from Sb to Bi and Cl to I. • The effective masses of the carriers are increasing linearly with the increasing band gaps. [ABSTRACT FROM AUTHOR]

Osmium based perovskites AOsO 3 (A=Ca, Sr and Ba) have been studied theoretically using density functional theory approach. These studies show that CaOsO 3 and SrOsO 3 are orthorhombic and BaOsO 3 is cubic and are consistent with the experiments. The electronic band structures demonstrate that these compounds are metals. The magnetic studies verify the experimental observations at low temperature, where the spin effects are canceled by the orbitals. The stable magnetic phase optimizations and magnetic susceptibilities calculations by the post-DFT treatment confirm that CaOsO 3 and SrOsO 3 are weak ferromagnetic whereas BaOsO 3 is a paramagnetic material. The directional magnetic study shows that these compounds are magnetically anisotropic, and reveals that the easy magnetization axis is [001] direction. [ABSTRACT FROM AUTHOR]

Electronic band structure, spontaneous polarization, hyperfine fields and electric field gradients (EFG) of the desirable multiferroic BiFeO 3 (BFO) are explored in R3c space group, using density functional theory. Improved TB-mBJ approach resolves the long-standing inconsistency between the theoretical and experimental band gap nature and value of BFO. In this study the calculated direct band gap is 2.84 eV, which was reported indirect band structures in other theoretical studies. The ferroelectric spontaneous polarization 88 μC/cm2 by PBE-GGA and 81 μC/cm2 by TB-mBJ were obtained using the Berry phase approach. Furthermore, the hyperfine interaction and EFG of the compound are also investigated. Image 1 • Bismuth ferrite (BiFeO 3) is attractive ferroelectric material. • The long-standing controversy in its experimental and theoretical band-gap is resolved. • The hyperfine fields and electric field gradients are calculated for the first time. • The spontaneous polarization of the compound is also explored. [ABSTRACT FROM AUTHOR]