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Electronic band structures, density of states, optical parameters, and structure properties of 2D layered halide perovskites Cs2MBr4 (M = Zn, Cd, Hg) are investigated using density functional theory (DFT). The structure optimization/relaxation was executed by generalized gradient approximation (GGA) and to handle band gap dependent properties (optical and electronic) modified Becke Johnson (GGA-mBJ) exchange potential was operated. In the structure composition of Cs2MBr4, the metal cations (M = Zn, Cd, Hg) build an isolated tetrahedra with bromine atoms i.e. [MBr4]2−. Eleven Cs atoms confine the tetrahedra and each Cs is surrounded by six tetrahedra, making an octahedral geometry [MBr4]62−. The calculated tolerance factors are greater than unity, confirming their orthorhombic crystal symmetry because perovskites having τ > 1 and large A-site cation destroy the 3D crystal structure. The bonds between octahedral layers are open and A-site (large-sized) cations connect two adjacent octahedra through intermolecular forces to form 2D- perovskite. The understudied 2D layered halide perovskites possess direct band gap nature and their band gap lies between 2.5–3.80 eV. The valence band edge is mainly attributed to M-d, M-s, and Br-4p orbitals, whereas the conduction band is dominated by M-s and Br-4p orbitals. The optical properties tell that these 2D perovskites are excellent dielectric and are prospective materials for optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this article the structure variations and relaxations, electric field gradient (EFG) and nuclear magnetic resonance (NMR) shielding of Cs2Pb(X1–uYu)4 (X/Y = Cl, Br, I and u = 0, 0.25, 0.5, 0.75, 1) are studied using density functional based calculations. The structure symmetry (space group) of the studied compounds are varying with the increment of halides at different sites. The space group of Cs2PbX4 is I4/mmm, while Cs2PbX2Y2 exist in the space group I4/mmm and P4/mmm, depending upon the halogen atomic coordinates. Similarly, Cs2PbX3Y and Cs2PbXY3 exist in three different crystal symmetries having space groups I4/mmm, P4/mmm and Pmm2. The ground state energies of Cs2Pb(X1–uYu)4 are lower in I4/mmm space group compared to P4/mmm and Pmm2, which show that these compounds are more stable in I4/mmm space group. NMR shielding increases with the increase in band gap energy, because the interaction of valence electrons and external magnetic field decreases. Density of states plot reveals that the Pb-5d orbital exists in the core region (σ-sphere about − 17.5 eV) and play a key role in NMR shielding, while the peaks of Cs-5p and X/Y-s orbitals exist at − 8 eV and − 12 eV respectively having contribution in NMR shielding. The negative contribution of the I-p state reduces the magnetic shielding effect (anti-bonding character increases), hence the applied external field strengthens. The electronic charge densities of Cs and Pb are elongated along z direction and make oblate distribution due to their negative electric field gradient ( V zz tot ), while the V zz tot values of halogens are positive, predict that the density of electronic charge compressed along the z direction and make prolate distribution. [ABSTRACT FROM AUTHOR]

Density functional calculations have been carried out to determine various physical properties of the perovskite molybdates AMoO3 (A = Ca, Sr, and Ba) using different exchange-correlation approximations including the generalized gradient approximation (GGA), GGA with Hubbard potential (GGA + U), and GGA with spin-orbit coupling (GGA + SOC), revealing that the strong spin-orbit coupling effect in these compounds is dominant. Based on their elastic properties, these compounds are expected to be mechanically stable, anisotropic, and ductile. Their electronic band structure and density of states indicate metallic nature due to hybridization of O p- and Mo d-states, and in particular delocalization of t2g orbital. The electrical properties indicate that these compounds will exhibit significant electrical conductivity above room temperature. The ground-state energy of different magnetic phases and post-DFT calculations showed that these compounds are nonmagnetic/paramagnetic. [ABSTRACT FROM AUTHOR]

In the present density functional studies, structural, mechanical and magneto-electronic properties of CaTaO 3, SrTaO 3 and BaTaO 3 perovskites have been investigated. The calculated structural parameters by DFT and analytical methods are found consistent with the experiments. The analytically calculated tolerance factors of these compounds as well as their mechanical properties show that they are stable in the cubic phase. Furthermore elastic properties show that these materials are ductile in nature and confirm that BaTaO 3 is harder than the rest compounds. The calculated spin dependent magneto-electronic properties reveal the paramagnetic metallic nature of these compounds. The electrical conductivity curve demonstrates significant conductivity above room temperature. On the basis of the presented properties it is expected that these compounds could be efficient electrode materials and need experimental investigations. [ABSTRACT FROM AUTHOR]

Abstract: The all electrons full potential linearized augmented plane waves (FP-LAPW) method with GGA+U is used to study SrTbO3 perovskite in cubic and orthorhombic phases. The structural parameters and ground state magnetic properties are found consistent with the experimental results. The electronic band structures and density of states demonstrate that SrTbO3 is a wide band gap semiconductor in both phases. The magnetic studies of the material show that the nature of the compound is G-type anti-ferromagnetic. The calculated magnetic moment of Tb+4 is found consistent with the experiments. Furthermore, the optical properties demonstrate that the optical gap of the material is 1.8eV, which lies in the visible region of the electromagnetic spectrum and hence the compound can be used in optoelectronic devices. [Copyright &y& Elsevier]

Theoretical studies of the cubic perovskite CaFeO3 are performed using the full potential linearized augmented plane-wave method with GGA+U. The calculated structural parameters are consistent with the experimental results. The tolerance factor reveals the cubic phase of the compound. The spin polarized electronic band structures and densities of states as well as the integer value of the magnetic moment of the unit cell (4µB) demonstrate that CaFeO3 is half metal. Ferromagnetism in CaFeO3 is due to Fe+4-O²-Fe+4 superexchange interaction. The robust properties of the compound show that with their compression up to a certain critical lattice constant, known as the robust transition lattice constant, an abrupt change in the electronic and magnetic properties occurs; the compounds lose their integer magnetic moment and become metallic. [ABSTRACT FROM AUTHOR]

In this article two-dimensional Ruddlesden-Popper (2DRP) halide perovskites Cs 2 B(X 1-u Y u) 4 where B = Pb, Sn; X/Y = Cl, Br, I; and u = 0, 0.25, 0.5, 0.75, 1 are investigated for potential applications in optoelectronic, photoemission and photovoltaic devices. In these compounds the corner sharing B-centered [BX 2 Y 4 ]4- units build the 2D [BX 2 Y 2 ] n 2n− plane, where the halides occupy the in-plane bridging and out of plane apical site respectively, while the spacer cation (Cs+) balancing the charge and separate the octahedral layers. These compounds have direct band gaps and spin orbit (SOC) calculations split Pb/Sn p-orbital and reduce the band gaps. The wide (1.04–3.45) and direct band gaps enable these materials for futuristic applications in optoelectronics, high speed ultrathin transistors and photodetectors. The anti-bonding lone-pair Pb/Sn-s orbital at the valence band edge is excellent for light absorption and photovoltaic performance. These compounds are good dielectric and optically functional materials for photovoltaic and energy storage devices due to their small values of charge carrier effective masses and large exciton binding energies. Therefore, the optical coefficients like dielectric function (real and imaginary), absorption coefficient and index of refraction are calculated. [ABSTRACT FROM AUTHOR]

Structural, electronic and magnetic properties of the perovskites SrFe 1-x Co x O 3 (x = 0, 0.25, 0.50, 0.75 and 1) are investigated using generalized gradient approximation (GGA) and GGA with Hubbard potential within the frame work of spin-polarized density functional theory (DFT). The calculated structural parameters and geometries are consistent with the experimental results and observed decrease in the lattice constants with increase in Co concentration. The bonding nature is visualized through electron charge densities and confirms that the bond between Sr−Fe/Co is ionic, Fe/Co−O is covalent and Co−Fe is metallic. Band profiles comparison and electrical properties reveal that these compounds are metallic. It is observed that the magnetic interaction is anti-ferromagnetic at Fe rich side while ferromagnetic for Co substituted compounds. The transition of anti-ferromagnetism to ferromagnetism is explained through exchange interactions. [ABSTRACT FROM AUTHOR]

The ground state structure and optoelectronic properties of novel quasi-2D layered halide perovskites CsPb 2 X 5 (X= Cl, Br, I) are investigated for the possible optoelectronic applications in light emitting, photodetectors, photoemission, and photovoltaic (PV) devices using first principle-based calculations of the density functional theory (DFT). In the structure composition of CsPb 2 X 5 , 2Pb2+ atoms coordinated with eight X- anions build [Pb 2 X 5 ]- polyhedral layers, where two layers of [Pb 2 X 5 ]- polyhedron are separated by Cs+ (spacer cation) layers. The band gap nature of the studied semiconductors is indirect and spin orbit coupling (SOC) effect reduces the band gaps and splits the Pb-p and X-p orbitals at the edges of conduction and valence bands respectively. The wide and suitable band gaps of CsPb 2 X 5 enable them for advanced technological applications in photodetectors, transistors, and optoelectronic devices. The dielectric functions, exciton binding energies, and carrier's effective masses show that CsPb 2 X 5 are suitable materials for optoelectronic, photodetectors, and light emitting devices. [ABSTRACT FROM AUTHOR]

Abstract: Structural, electronic and magnetic properties of cubic perovskite SnTaO3 have been investigated for the first time using the full potential linearized augmented plane wave (FP-LAPW) method within the frame work of density functional theory (DFT). The calculated lattice constant is found consistent with the experimental results, while the electronic band structure shows that SnTaO3 is metallic. The electronic cloud of the material demonstrates that the bond nature between Ta and O is covalent, whereas between Sn and O is ionic. The spin up and spin down band profiles for the compound are found symmetric, which reveal no spin polarization at the Fermi level. Furthermore the magnetic moments of the adjacent atoms and as a whole are very weak. Hence our results show that SnTaO3 behaves much like a simple metal paramagnetic. No such experimental evidence for SnTaO3 is existed. The overall study of the simple metallic nature of SnTaO3 predicts that it can be used as a new electrode material. [Copyright &y& Elsevier]

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]

DFT studies are performed to investigate the structural, mechanical and magneto-electronic properties of the TlTF 3 (T=Fe, Co and Ni) perovskites for the first time using GGA, GGA+U and hybrid density functional theory (HF). Our calculations show that HF give better results than GGA and GGA+U and more consistent with the experiments. The comparison of the lattice constants calculated by HF with experiments shows a maximum underestimation less than 0.2%. The chemical bonding between different ions in these compounds is explained on the bases of electronic clouds, which reveals that in TlFeF 3 , Fe has more ionic character with F than the rest. The mechanical properties explain the hardness of these compounds and show that TlFeF 3 is more ductile. Spin-dependent electronic band profiles show that TlFeF 3 and TlCoF 3 are metallic, whereas TlNiF 3 is pseudo direct wide bandgap semiconductor. The stable magnetic phase optimizations and the calculated magnetic susceptibility confirm that TlFeF 3 and TlNiF 3 are ferromagnetic whereas TlCoF 3 is anti-ferromagnetic material. [ABSTRACT FROM AUTHOR]

Ferromagnetic metallic inverse-perovskite (Eu 3 O)In is studied using hybrid functional theory (HF) in the frame work DFT. The calculated structural parameters and geometries of the material are calculated by different exchange correlation potentials and found that HF results are closed to the experiments. Electronic charge density explains the bond nature and polarization. The spin polarized electronic band profiles and density of states reveal the metallic nature of the compound. The Eu f-state splitting show that the valance bands are dominated mainly by f-[a 2 ], f-[x(T 1 )], f-[y(T 1 )] and f-[z(T 1 )] states. The ground state magnetic phase of the compound is optimized. The optimum energy and magnetic susceptibility confirm the ferromagnetic nature of the compound. On the basis of different properties presented it is predicted that this compound is magnetoresistive material. [ABSTRACT FROM AUTHOR]

Highlights: [•] Anti-perovskites NiNMn3 and ZnNMn3 are theoretically investigated. [•] The electronic band structure reveals that both compounds are metals. [•] The optimized ground state magnetic phases of both compounds are anti-ferromagnetic. [•] The magnetic properties show that they can be used in spin based devices. [Copyright &y& Elsevier]

Abstract: Structural and electronic properties of the cubic perovskite ZnTiO3 and spinel Zn2TiO4 are theoretically studied by the modified Becke–Johnson (mBJ) potential within the framework of density functional theory (DFT). The calculated lattice constants are found to be consistent with the experimental results. The electronic band structures of both the materials reveal that ZnTiO3 is an indirect band gap while Zn2TiO4 is a direct band gap semiconductor. The calculated fundamental band gaps of these compounds are 2.7eV and 3.18eV, which are consistent with the experimental band gaps of 2.9eV and 3.1eV, respectively. Zn2TiO4 is a wide and direct band gap compound and hence is an attractive material for optoelectronic applications, especially in near ultraviolet (UV) optoelectronics. Keeping in view the importance of Zn2TiO4 in low frequency UV devices its optical properties like dielectric functions, refractive index, reflectivity and energy loss function are also evaluated and discussed in detail. [Copyright &y& Elsevier]

Theoretical studies of the cubic perovskite CaFeO3 are performed using the full potential linearized augmented plane-wave method with GGA+U. The calculated structural parameters are consistent with the experimental results. The tolerance factor reveals the cubic phase of the compound. The spin polarized electronic band structures and densities of states as well as the integer value of the magnetic moment of the unit cell (4µB) demonstrate that CaFeO3 is half metal. Ferromagnetism in CaFeO3 is due to Fe+4-O²-Fe+4 superexchange interaction. The robust properties of the compound show that with their compression up to a certain critical lattice constant, known as the robust transition lattice constant, an abrupt change in the electronic and magnetic properties occurs; the compounds lose their integer magnetic moment and become metallic. [ABSTRACT FROM AUTHOR]