Search

In this theoretical study we investigate the electronic, optical, and photocatalytic properties of monolayer titanium dioxide (TiO2), nickel dioxide (NiO2), and germanium dioxide (GeO2), as well as the effects of strain and stacking on these monolayers. The first principle calculations were performed using density functional theory (DFT) to determine the band structure, density of states, and optical properties of the monolayers. The photocatalytic activity of the monolayers was evaluated based on the water-splitting reaction. The results showed that the electronic and optical properties of the monolayers were significantly affected by strain and stacking. Specifically, the bandgap of TiO2, NiO2, and GeO2 decreased under tensile strain, while it increased under compressive strain. Furthermore, the stacking order of the monolayers affected their electronic and optical properties. The photocatalytic activity of the monolayers was found to be highest for TiO2. This study provides a valuable insight into the properties of monolayer oxides TiO2 and GeO2 and their van der Waal heterostructure GeO2–TiO2 as a potential candidate for photocatalytic water splitting. [ABSTRACT FROM AUTHOR]

Electronic structure, optical, and photocatalytic properties of P, BSe, and SiC monolayers and their van der Waals heterostructures are investigated by (hybrid) first-principle calculations. The stability of the heterostructures and their corresponding induced-strain/unstrain monolayers are confirmed by the phonon spectra calculations. Similar to the corresponding parent monolayers, P-BSe (BSe-SiC) heterostructures are indirect type-II (type-I) bandgap semiconductors. A tensile strain of 10% (2%) transforms P-BSe (BSe-SiC) to type-I (type-II) direct bandgap nature. Interestingly, irrespective of the corresponding monolayers, the P-SiC heterostructure is a direct bandgap (type-II) semiconductor. The calculated electron and hole carrier mobilities of these heterostructures are in the range of 1.2 × 10 4 cm 2 / Vs to 68.56 × 10 4 cm 2 / Vs. Furthermore, absorption spectra are calculated to understand the optical behavior of these systems, where the lowest energy transitions are dominated by excitons. The valence and conduction band edges straddle the standard redox potentials in P-BSe, BSe-SiC, and P-SiC (strained) heterostructures, making them promising candidates for water splitting in the acidic solution. An induced compressive strain of 3.5% makes P suitable for water splitting at pH = 0. [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]

Structural, electronic and magnetic properties of the quaternary perovskites LnMn3V4O12 (Ln = La, Nd and Gd) are calculated using generalised gradient approximation along with Hubbard potential (GGA + U) within the frame work of density functional theory (DFT). It is observed that the calculated lattice constants are decreases as going from La→Gd due to the lanthanide's contraction and found consistent with the experiments. The electron charge densities show that the Ln—O bond is ionic whereas the bond between Mn/V—O is covalent. The metallic nature of these compounds is confirmed by the overall band structures. The magnetic susceptibility curves show that all these compounds are anti-ferromagnetic and the exchange interactions play vital role in the magnetic properties of these perovskites. Furthermore, the electrical resistivities calculated by BoltzTrap code also verify the metallic nature of all these compounds. This study also confirms that in these compounds Mn 3d-states electrons are responsible for the magnetic behaviour whereas V 3d-states electrons for the electronic behaviour. [ABSTRACT FROM AUTHOR]

Abstract In this paper, van der Waals heterostructures consisting of MX 2 (M = Zr, Hf and X = S, Se) monolayers are modeled. The favorable stacking and stability of the modeled monolayer heterostructures are confirmed through binding energy and phonon dispersion calculations. After confirming stability, the electronic and thermoelectric properties of these compounds are explored using the first-principles calculations combined with semiclassical Boltzmann transport theory. It is found that type-II band alignment in ZrS 2 HfSe 2 facilitates charge separation for optoelectronics and solar energy conversion. All studied heterostructures show remarkably higher electrical conductivity than corresponding monolayers, responsible for large power factor values, especially at 1200 K. These findings indicate that the creation of van der Waals heterostructures from MX 2 may be promising for efficient optoelectronic and thermoelectric devices. Highlights • First-principles study of structural, electronic and thermoelectric performance of van der Waals heterostructures of MX 2 (M = Zr, Hf and X = S, Se) monolayers. • Dynamical stability of all under study heterostructures. • Type-II band alignment in ZrS 2 -HfSe 2. • van der Waals heterostructures of MX 2 (M = Zr, Hf and X = S, Se) are promising for efficient optoelectronic and thermoelectric devices. [ABSTRACT FROM AUTHOR]

In this paper, structural, electronic and magnetic properties of the aluminum-rich intermetallic alloy Al13Fe4 are investigated using full potential linearized augmented plane waves (FPLAPW) approach in the frame work of density functional theory (DFT). The calculated structural parameters are consistent with the experimentally reported data. In this alloy, Fe atoms possess different coordination numbers with Al atoms, i.e., Fe(1) and Fe(2) have the same coordination number 5, whereas Fe(3), Fe(4) and Fe(5) have 4, 7 and 9 coordination numbers, respectively. The compound is found metallic and ferromagnetic in nature. Post-DFT (BoltzTraP code) calculations confirm the ferromagnetic and anisotropic behavior. The Fe(5) atom plays a central role in the electronic and magnetic properties of the alloy due to the large coordination with Al atom as compared to the rest Fe atoms. [ABSTRACT FROM AUTHOR]

Organic-Inorganic perovskites CsPbX 3 (X = Cl, Br, I) are investigated for their potential ability and use as solar cells and energy storage materials, using density function theory, generalized gradient approximation and modified Becke-Johnson (TB-mBJ) exchange potential. Structural analysis shows that the lattice constant and unit cell volume varies when CsPbX 3 (X = Cl, Br, I) change from cubic phase to tetragonal and orthorhombic structures. The electronic properties show that CsPbCl 3 , CsPbBr 3 and CsPbI 3 all are semiconductor in with bandgap between 0.79 eV and 2.54 eV. It is also observed that the bandgap changes when the structure changes. Optical properties show that these materials have a good absorption ability of photons due to their narrow bandgaps. The real ε 1 (ω) and imaginary ε 2 (ω) parts of their dielectric functions show that CsPbCl 3 , CsPbBr 3 and CsPbI 3 also possess a great ability of retaining the energy it absorbs. These properties make them very suitable for solar cells and energy storage applications. These materials also behave as superluminescent material at high photon energy. [ABSTRACT FROM AUTHOR]

In this article we communicate the spin-orbit interaction effects on the thermoelectric properties of alkaline-earth (A = Ca, Sr and Ba) based fully filled skutterudites ACo 4 Sb 12 . From the electronic structure calculations for ACo 4 Sb 12 (A = Ca, Sr and Ba) it is understand that spin-orbit coupling take part in splitting of the states of the materials, however in case of BaCo 4 Sb 12 , with splitting, the maximum peak around the Fermi level also becomes sharper. This in turn affects the thermal performance of this material. Maximum peak value of Seebeck coefficient is significantly reduced for CaCo 4 Sb 12 and SrCo 4 Sb 12 , however in case of BaCo 4 Sb 12 Seebeck coefficient is increased significantly in the lower chemical potential region for n-type doping when spin-orbit coupling is added to the calculations. Furthermore there is also reduction in the electrical and electronic thermal conductivities for all compounds CaCo 4 Sb 12 , SrCo 4 Sb 12 and BaCo 4 Sb 12 , due to spin-orbit interaction. Maximum zT’s values obtained without spin-orbit interaction for CaCo 4 Sb 12 , SrCo 4 Sb 12 and BaCo 4 Sb 12 are 0.97, 0.95 and 0.64 whereas with the spin-orbit interaction maximum zT’s values are 0.64, 0.59 and 0.69 respectively. [ABSTRACT FROM AUTHOR]

In this paper we explore the electronic nature and thermoelectric properties of filled skutterudites AFe 4 Sb 12 (A Ca, Sr and Ba) by DFT and post-DFT techniques. The calculated results show that the filling of Ca, Sr, and Ba at the empty crystal sites enhances the thermoelectric performance of the host material. This increase is a consequence of the coupling between the guest and the host atoms, which affects the electronic density at different symmetry points that increases the density of states of the valence bands. The valence band edge is almost independent of the guest atoms, i.e., the s-bands of Ca, Sr and Ba have negligibly small contribution to the valence band edge. In these compounds, the maximum value of thermoelectric PF/τ of 42.43 × 10 14 μW/cmK 2 s and 33.57 × 10 14 μW/cmK 2 s for the n-type of SrFe 4 Sb 12 in the spin-up and down states respectively. The striking feature of these compounds is their effectiveness at the low chemical potential values for the best thermoelectric performance. [ABSTRACT FROM AUTHOR]

DFT is used to study various transition metal based ceramics LiAA′O 6 (A = Nb, Ta, and A′ = W, Mo) in tetragonal phase with space group 421 m (No. 113). The calculated structural and geometrical parameters are found in closed agreement with the experiments. Electronic clouds explain the chemical bonding and reveal that Li atom occupy central position and form ionic bond. Other bonds in these compounds are significantly covalent due to the sharing of electrons between O and A/A′. The electronic properties demonstrate that these compounds are wide bandgap semiconductors in the energy range of 2.18–2.60 eV. These bandgap energies confirm the suitability of these oxides in optoelectronic devices operating in the visible range of the electromagnetic spectrum. [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]

We present a review on the research developments on the theoretical electronic properties of the antiperovskite materials. The antiperovskite materials have perovskite type structure with the positions of cations and anions interchanged. The electronic structures are used to explain different physical properties of materials; therefore it is crucial to understand band structures and densities of states of materials for their effective use in technology. The theoretical results of the electronic structure of antiperovskites were discussed and compared with the available experimental results to measure the accuracy of the research done so far on these materials. The important physical properties of these compounds like magnetic properties and superconductivity are also highlighted. Nevertheless the thermoelectric properties of these materials are still unexplored except for a few reports which suggest that antiperovskite materials may be potential candidates for thermoelectric generators. [ABSTRACT FROM AUTHOR]

Structural, elastic, electronic and magnetic properties of the transition metals based perovskites SrTMO 3 (TM = Mn, Fe, Co, Tc, Ru, Rh, Re, Os, Ir) are investigated using advanced exchange-correlation methods based on density functional theory (DFT). The calculated structural parameters are found consistent with the experiments. The elastic properties reveal that these compounds are anisotropic, mechanically stable and ductile except SrMnO 3. Electronic properties show that the strong hybridization between TM-d and O-2p states at the Fermi level make these compounds metallic expect SrMnO 3 which is half-metal. The electrical resistivity indicates that these compounds are good conductors at room temperature. Magnetic ordering and magnetic susceptibility show that SrMnO 3 , SrFeO 3 and SrTcO 3 are G-type antiferromagnetic; SrCoO 3 , SrRuO 3 and SrOsO 3 are ferromagnetic, whereas SrRhO 3 , SrReO 3 and SrIrO 3 are paramagnetic/non-magnetic compounds. The study also confirms that TM-3d perovskites are strongly correlated electron systems while spin-orbit coupling effect is dominant in TM-5d perovskites. [ABSTRACT FROM AUTHOR]

Structural, electronic, optical and magnetic properties of titanium based perovskites La 2 MTiO 6 (M = Co, Ni, Cu and Zn) are investigated in monoclinic phase with space group (P2 1 /n) in the domain of density functional theory (DFT). The generalized gradient approximation plus Hubbard potential (GGA + U) is utilized to study these high correlated electrons systems. Structural parameters are found in closed agreement with experiments. Cohesive energy reveals that La 2 CoTiO 6 is more stable among these compounds. The electronic properties show the semiconductor behavior of these compounds with band gap varies from 1.02 to 2.3 eV. Optical properties demonstrate that all these compounds are potential candidates for optoelectronic devices. The electrical resistivity which increases in a sequence from Co to Zn also confirms the semiconductor nature of these compounds. The magnetic susceptibility curves show that La 2 CoTiO 6 , La 2 NiTiO 6 and La 2 CuTiO 6 are antiferromagnetic whereas La 2 ZnTiO 6 is a paramagnetic material. Based on the semiconductor antiferromagnetic nature of La 2 CoTiO 6 , La 2 NiTiO 6 and La 2 CuTiO 6 it is expected that these compounds could be used as pinning layers in spin valves and storage devices. • La 2 MTiO 6 (M = Co, Ni, Cu and Zn) perovskites are semiconductors with band gaps ranges from 1.2 to 2.3 eV. • These compounds are optically active in the broad range electromagnetic spectrum. • Electrical resistivity increases in a sequence from Co to Zn and confirms the semiconductor nature of these compounds. • Perovskites La 2 CoTiO 6 , La 2 NiTiO 6 and La 2 CuTiO 6 are antiferromagnetic whereas La 2 ZnTiO 6 is a paramagnetic material. [ABSTRACT FROM AUTHOR]

Two-dimensional magnetic materials are high desirable for realizing advanced optoelectronic and spintronic devices. In this paper, we report systematic studies the effects of strain on the electronic structure, magnetic states and optical properties of Mn-doped SnS 2 monolayer (ML) by means of first-principles calculations. Ab-initio molecular dynamics simulations and formation energy reveal that the Mn-doped SnS 2 ML is stable at 500 K and can be fabricated under the S-rich condition. The substitution of a Mn for a Sn atom induces 3 μ B magnetic moment in nonmagnetic SnS 2 ML, which is consistent with the Hund's rule and Aufbau principle. Based on classical Heisenberg model and mean-field approximation the Curie temperature is calculated to be 476.13 K. Due to symmetry reserved crystal structure, the net magnetic moment of Mn-doped SnS 2 ML is robust even if considerable strains (−10 to 10%) are applied. The blue-shift and red-shift of the absorption peaks are observed in the optical spectrum by biaxial compressive and tensile strains. The biaxial strain effectively improves the optical properties of Mn-doped SnS 2 ML, particularly in the visible light region. This study provide useful guidance for practical application in magnetic and optoelectronic devices. The VBM and CBM shifts of the Mn-doped SnS 2 ML under biaxial strain. [Display omitted] • The electronic, magnetic and optical properties of Mn-doped SnS 2 monolayer are studied. • Mn-doped SnS 2 monolayer is stable at 500 K and can be fabricated under S-rich condition. • Under biaxial strain the Mn-doped SnS 2 monolayer is always a magnetic semiconductor with 3 μ B moment. • The optical properties of Mn-doped SnS 2 monolayer can be tuned by biaxial strain. • Mn-doped SnS 2 monolayer is a vigorous nominee for optoelectronic applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new class of MX 2 (M = Mo, W; X = S, Se) monolayers with general formula MXY or XMY, have been successfully synthesized by chemical vapor deposition of Se(S) in MoS 2 (MoSe 2). • Optimized ZrSSe, HfSSe monolayers and ZrSSe/HfSSe vdW heterostructure are indirect band gap semiconductors. • A transition from an indirect to direct band gap is achieved for tensile strain of 6(8)% for ZrSSe(HfSSe) monolayer. • ZrSSe, HfSSe monolayers and type-II ZrSSe/HfSSe vdW heterostructure heterostruture under tensile strain are efficient photocatalysts. We investigated the effects of biaxial strain on electronic structure of ZrS 2 , ZrSe 2 , HfS 2 , HfSe 2 , ZrSSe and HfSSe monolayers. Similar to ZrS 2 , ZrSe 2 , HfS 2 , HfSe 2 monolayers, Janus ZrSSe and HfSSe monolayers are indirect bandgap semiconductors. Tensile strain of 6(8)% transform ZrSSe(HfSSe) monolayer to direct bandgap semiconductor. Based on the calculation of binding energies and interlayer distance staking-(c) is found to be the most stable configuration for ZrSSe/HfSSe vdW heterostructure. Unstrained ZrSSe/HfSSe vdW heterostructure in staking-(c) is a type-II indirect bandgap semiconductor. Valence and conduction band edges show that under tensile strain ZrSSe, HfSSe and ZrSSe/HfSSe vdW heterostructure are efficient photocatalysts. [ABSTRACT FROM AUTHOR]

Mg-rich intermetallic NdNiMg 5 in orthorhombic phase with space group Cmcm (No. 63) has been studied theoretically using hybrid functional (HF–B3PW91) within the frame work of density functional theory (DFT). The calculated structural parameters and geometries are found in good agreement with the experiments. The electronic properties of the material reveal the metallic nature. Nd 4f-states splitting show that A 2 , y[t 1 ] and z[t 1 ] contributed in the valence band; x[t 1 ], ksi[t 2 ] and eta[t 2 ] in conduction band; where zeta[t 1 ] state completely lay at the Fermi level make the compound metallic. The electrical properties show that the material has significant conductivity above the room temperature. The stable magnetic phase of the compound is optimized which show that the material is stable in G-type antiferromagnetic (AFM) phase and Nd–Ni direct magnetic exchange interactions are involved. The calculated effective magnetic moments of Nd is 3.70 μ B per unit cell. The post-DFT calculations also confirm the AFM phase of the compound with Neel temperature (T N) = 25 K and Curie-Weiss constant (θ) = −23 K. Based on the above physical properties it is expected that this intermetallic could be used in spin valve and magnetic memory devices. • Mg-rich intermetallic NdNiMg 5 has been investigated theoretically using hybrid density functional theory. • The electronic properties of the material reveal the metallic nature. • The electrical properties show that the material has significant conductivity above the room temperature. • Stable magnetic phase of the compound is G-type anti-ferromagnetic phase. • The post-DFT calculations also confirm the AFM phase of the compound. [ABSTRACT FROM AUTHOR]

AMn 3 V 4 O 12 (A = Ca, Ce and Sm) quaternary perovskites are studied in the domain of density functional theory using various potentials. Generalized gradient approximation along with Hubbard U and hybrid density functional schemes are found effective tools for the treatment of these compounds. Changing of A-site cation, affects the physical properties due to the valence distributions Ca+2Mn+2 3 V+4 4 O 12, Ce+3Mn+2 3 V+3.75 4 O 12 and Sm+3Mn+2 3 V+3.75 4 O 12 respectively. Cohesive energy and enthalpy show that these compounds are thermodynamically stable. Electronic and electrical properties reveal the semi-metallic nature of these compounds. It is observed that in these compounds Aʹ-site (Mn) 3d electrons are localized and responsible for the magnetic properties whereas B-site (V) 3d electrons are delocalized, contributed in the electronic behavior. The elastic properties also confirm the stability and demonstrate that these compounds are ductile in nature. DFT as well as post−DFT treatments verify the anti-ferromagnetic nature of these compounds with the dominant Mn+2―O−2―Mn+2 super exchange interactions. • Cohesive energy and enthalpy show that these perovskites are thermodynamically stable. • Elastic properties confirm the stability and demonstrate that these compounds are ductile. • Electronic band profiles and electrical properties reveal the semi-metallic nature of the compounds. • These compounds are anti-ferromagnetic with the dominant Mn+2―O−2―Mn+2 super exchange interactions. [ABSTRACT FROM AUTHOR]