Structural,elastic, electronic and optical properties of the cubic perovskite BiAlO3

We report first-principles study of structural, elastic, electronic and optical properties of the cubic perovskite-type BiAlO₃ using the pseudopotential plane waves method within the local density approximation. The calculated structural parameters are in good agreement with previous calculations. The elastic constants and their pressure dependence are calculated using the static finite strain technique. A linear pressure dependence of the elastic stiffness is found. Band structures show that BiAlO₃ has an indirect band gap between the occupied O 2p and unoccupied Bi 6p states. The density of states and Mulliken charge populations analysis shows that Al–O and Bi–O bonds are covalent with a strong hybridization. The variation of the gap versus pressure is well fitted to a quadratic function and an indirect to direct band gap transition occurs at 15.5 GPa. Furthermore, in order to understand the optical properties of BiAlO₃, the dielectric function, absorption coefficient, refractive index, extinction coefficient, optical reflectivity and electron energy loss are calculated for radiation up to 30 eV.     

Structural, electronic, and optical properties of CaCO3 aragonite

Density functional theory ab initio calculations of the structural parameters, electronic structure, carriers effective masses, and optical absorption of the CaCO₃ aragonite polymorph were performed within the local density and generalized gradient approximations, local density approximation (LDA) and generalized gradient approximation (GGA) respectively. A good agreement between the calculated lattice parameters and experimental results was obtained. Both the LDA and GGA results for CaCO₃ aragonite exhibit very close indirect and direct energy gaps, and the computed effective masses are heavy and anisotropic. Two optical absorption regimes related to distinct electronic transitions are predicted by the calculations.     

Borazine-based conjugated derivatives: Structural,electronic, and optical properties

The structural characteristics, electronic properties, and nonlinear optical properties of borazine-based conjugated derivatives have been explored at B3LYP/6-311G(d,p) level. The effects of various electron donor and acceptor substituents (H, F, Cl, Br, Me, CF₃, NH₂, OH, COOH, CHO, NO₂) on the structure, polarizability, frontier orbitals, the most intense electronic transition, and hyperpolarizabilities have studied. Calculations show that NO₂-substituted molecules have lowest hardness, the largest isotropic polarizability and anisotropy of polarizability, and first hyperpolarizability.     

Structural,electronic, and optical properties of some new dithienosilole derivatives

Structural Chemistry - Structural, electronic, and optical properties of a series of organic semiconductors based on dithienosilole (DTS) and its derivatives were theoretically studied using...     

Structural,elastic, electronic and optical properties of the newly synthesized monoclinic Zintl phase BaIn2P2

The present study explores the structural, elastic, electronic and optical properties of the newly synthesized monoclinic Zintl phase BaIn₂P₂ using a pseudopotential plane-wave method in the framework of density functional theory within the generalized gradient approximation. The calculated lattice constants and internal coordinates are in very good agreement with the experimental findings. Independent single-crystal elastic constants as well as numerical estimations of the bulk modulus, the shear modulus, Young's modulus, Poisson's ratio, Pugh's indicator of brittle/ductile behaviour and the Debye temperature for the corresponding polycrystalline phase were obtained. The elastic anisotropy of BaIn₂P₂ was investigated using three different indexes. The calculated electronic band structure and the total and site-projected l-decomposed densities of states reveal that this compound is a direct narrow-band-gap semiconductor. Under the influence of hydrostatic pressure, the direct D–D band gap transforms into an indirect B-D band gap at 4.08 GPa, then into a B–Γ band gap at 10.56 GPa. Optical macroscopic constants, namely, the dielectric function, refractive index, extinction coefficient, reflectivity coefficient, absorption coefficient and energy-loss function, for polarized incident radiation along the [100], [010] and [001] directions were investigated.     

Structural, electronic, and magnetic properties of UFeS3 and UFeSe3

Black prisms of UFeS(3) and UFeSe(3) have been synthesized by solid-state reactions of U, Fe, and S or Se with CsCl as a flux at 1173 K. The structure of these isostructural compounds consists of layers of edge- and corner-sharing FeS(6) or FeSe(6) octahedra that are separated by layers of face- and edge-sharing US(8) or USe(8) bicapped trigonal prisms. The isomer shifts in the iron-57 M?ssbauer spectra of both UFeS(3) and UFeSe(3) are consistent with the presence of high-spin iron(II) ions octahedrally coordinated to S or Se. The XANES spectra of UFeS(3) and UFeSe(3) are consistent with uranium(IV). Single-crystal magnetic susceptibility measurements along the three crystallographic axes of UFeSe(3) reveal a substantial magnetic anisotropy with a change of easy axis from the a-axis above 40 K to the b-axis below 40 K, a change that results from competition between the iron(II) and uranium(IV) anisotropies. The temperature dependence of the magnetic susceptibility along the three axes is characteristic of two-dimensional magnetism. A small shoulder-like anomaly is observed in the magnetic susceptibilities along the a- and b-axes at 96 and 107 K, respectively. Below 107 K, the iron-57 M?ssbauer spectra of UFeS(3) and UFeSe(3) show that the iron nuclei experience a magnetic hyperfine field that results from long-range magnetic ordering of at least the iron(II) magnetic moments because the field exhibits Brillouin-like behavior. Below 40 K there is no significant change in the M?ssbauer spectra as a result of change in magnetic anisotropy. The complexity of the iron-57 M?ssbauer spectra and the temperature and field dependencies of the magnetic properties point toward a complex long-range magnetic structure of two independent iron(II) and uranium(IV) two-dimensional sublattices. The temperature dependence of the single-crystal resistivity of UFeSe(3) measured along the a-axis reveals semiconducting behavior between 30 and 300 K with an energy gap of about 0.03 eV below the 53 K maximum in susceptibility, of about 0.05 eV between 50 and 107 K, and of 0.03 eV above 107 K; a negative magnetoresistance was observed below 60 K.     

Structural, electronic, and optical properties of phosphole-containing pi-conjugated oligomers for light-emitting diodes

The purpose of this work is to provide an in-depth interpretation of the optical and electronic properties of a series of phosphole derivatives, including 2,5-diphenylthiooxophosphole (2a), 2-phenyl-5-biphenylthiooxophosphole (3a), 2-phenyl-5-stilbenylthiooxophosphole (4a), 2,5-dithienylthiooxophosphole (2b), 2-thienyl-5-biphenylthiooxophosphole (3b), 2-thienyl-5-stilbenylthiooxophosphole (4b), and dibenzophosphole 1. These thiooxophospholes show great potential for application in OLEDs as efficient red emitters due to the tuning of the optical and electronic properties by the use of various substituents at the 2,5-positions of the phosphole ring. The geometric and electronic structures of the oligomers in the ground state were investigated using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited states were optimized with ab initio CIS. To assign the absorption and emission peaks observed in the experiment, we computed the energies of the lowest singlet excited states with time-dependent DFT (TD-DFT). All DFT calculations were performed using the B3LYP functional and the 6-31G (d) basis set. The results show that the HOMOs, LUMOs, energy gaps, ionization potentials, and electron affinities for the phosphole derivatives are significantly affected by varying the phosphole ring substituents at the 2,5-positions, which favor the hole and electron injection into OLEDs. The absorption and emission spectra exhibit red shifts to some extent [the absorption spectra: 339.63 (1)<358.65 (2a)<373.77 (3a)<443.89 nm (4a) and 403.03 (3b)<449.11 (2b)<460.19 nm (4b); the emission spectra: 418.42 (1)<513.62 (2a)<556.51 (3a)<642.59 nm (4a) and 568.31 (2b)<631.11 (3b)<647.35 nm (4b)] and the Stokes shifts are unexpectedly large ranging from 78 to 228 nm resulting from a more planar conformation of the excited state for the phosphole derivatives.     

Structural and optical properties of sprayed Zn1−xMnxO films

In recent years the dilute magnetic semiconductors have received much attention due to the complementary properties of semiconductor and ferromagnetic behaviour. Zn_1−xMn_xO thin films have been synthesized by chemical spray pyrolysis at a substrate temperature of 400 °C with different manganese compositions that vary in the range, 0.0 ≤ x ≤ 0.25, on Corning 7059 glass substrates. The X-ray diffraction studies revealed that all the films were strongly oriented along the (002) orientation corresponding to the hexagonal wurtzite structure. The crystalline quality of the layers was found to decrease with the increase of x, however, no structural changes were observed over the ‘Mn’ composition range investigated. The optical absorption studies revealed that the energy band gap of the films followed the Vegard's law. The optical band gap of the films prepared at x = 0.15 was found to be ∼3.35 eV. The photoluminescence characteristics of Zn_1−xMn_xO films showed an emission peak at around 390 nm with a broad band about 530 nm. The details of these results were reported and discussed.     

Structural, electronic, and optical properties of 9-heterofluorenes: a quantum chemical study

Density-functional theory studies were applied to investigate the structural, electronic, and optical properties of 9-heterofluorenes achieved by substituting the carbon at 9 position of fluorene with silicon, germanium, nitrogen, phosphor, oxygen, sulfur, selenium, or boron. These heterofluorenes and their oligomers up to pentamers are highly aromatic and electrooptically active. The alkyl and aryl substituents of the heteroatom have limited influence, but the oxidation of the atom has significant influence on their molecular structures and properties. The highest occupied molecular orbital (HOMO)-lowest occupied molecular orbital (LUMO) interaction theory was successfully applied to analyze the energy levels and the frontier wave functions of these heterofluorenes. Most heterofluorenes belong to type B of interaction with low-lying LUMO and have the second kind of wave function. Carbazole and selenafluorene have type C of interaction with high-lying HOMO and the third kind of wave function. Types C and D of heterofluorenes, such as carbazole, oxygafluorene, sulfurafluorene, and selenafluorene also have high triplet state energies. The extrapolated HOMO and LUMO for polyheterofluorenes indicate that polyselenonafluorene has the lowest LUMO; polycarbazole has the highest HOMO; polyselenafluorene has the highest bandgap (E(g)); and polyborafluorene has the lowest E(g). Heterofluorenes and their oligomers and polymers are of great experimental interests, especially those having extraordinary properties revealed in this study.     

Strain-tunable electronic properties and optical properties of Hf2CO2 MXene

Two-dimensional materials have been extensively applied because of their unusual electronic, mechanical, and optical properties. In this paper, the electronic structure and optical properties of Hf₂CO₂ MXene under biaxial and uniaxial strains are investigated by the Heys-Scuseria-Ernzerhof (HSE06) method. Monolayer Hf₂CO₂ can sustain stress up to 6.453 N/M for biaxial strain and 3.072 N/M for uniaxial strain. Monolayer Hf₂CO₂ undergoes the transition from semiconductor to metal under −12% strain whether it is under biaxial or uniaxial strain. With the increasing biaxial compressive strain, the blue shift of Hf-d, O-p, and C-p orbitals in valence band maximum results in the metallization of monolayer Hf₂CO₂, while the red shift of Hf-d and O-p orbitals in conduction band minimum results in the metallization of monolayer Hf₂CO₂ with increasing uniaxial compressive strain. The analysis of optical properties indicates that uniaxial strain weakens the reflectivity and refractive index of monolayer Hf₂CO₂ in the visible-light range. In addition, the effective mass and the charge distribution under biaxial and uniaxial strains are also explored.     

Structural, electronic, and magnetic properties of fe(3)c(2) cluster

On the basis of density-functional theory and all-electron numerical basis set, 20 stable isomers of Fe(3)C(2) cluster are found through optimization calculations and frequency analysis from 108 initial structures. A nonplanar C(s) structure with nonet spin multiplicity and 482.978 kcal/mol of binding energy is found as the candidate of global minimum geometry of Fe(3)C(2) cluster. The binding energies, the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, and the magnetic moments of all the isomers are reported. The relationship between the molecular properties and geometrical structures is also investigated.     

First principles prediction of the elastic,electronic, and optical properties of Sb2S3 and Sb2Se3 compounds

We have performed a first principles study of structural, mechanical, electronic, and optical properties of orthorhombic Sb₂S₃ and Sb₂Se₃ compounds using the density functional theory within the local density approximation. The lattice parameters, bulk modulus, and its pressure derivatives of these compounds have been obtained. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work. The linear photon-energy dependent dielectric functions and some optical properties such as the energy-loss function, the effective number of valence electrons and the effective optical dielectric constant are calculated. Our structural estimation and some other results are in agreement with the available experimental and theoretical data.     

Structural, electronic, and magnetic properties of manganese-doped Zn12O12 clusters: a first-principles study

A first-principles study has been performed to evaluate the structural, electronic, and magnetic properties of Zn(12)O(12) clusters doped with one or two Mn atoms. The substitutional, exohedral, and endohedral dopings are taken into account. For the monodoped clusters, the substitutional isomer is most energetically favorable, and an exohedral isomer may appear as a low-lying metastable state. All isomers present 5 mu(B) magnetic moment that is mainly contributed by the Mn-3d component. For the bidoped clusters, the antiferromagnetic state is degenerate with the ferromagnetic state at larger Mn-Mn distance (>5 A), while it is more energetically favorable at smaller Mn-Mn distance. Thus, the cohesion of bidoped isomer is sensitive to the magnetic coupling or chemical bonding. The endohedral bidoped isomer is found to be a stable local minimum, and the direct Mn-Mn interaction causes the reduction of local magnetic moment of Mn to about 4 mu(B).     

Structural,elastic, electronic and thermal properties of the cubic perovskite-type BaSnO3

First-principles calculations are performed to investigate the structural, elastic, electronic and thermal properties of the cubic perovskite-type BaSnO₃. The ground-state properties are in agreement with experimental data. The independent elastic constants, C₁₁, C₁₂ and C₄₄, are calculated from direct computation of stresses generated by small strains. A linear pressure dependence of the elastic stiffnesses is found. From the theoretical elastic constants, we have computed the elastic wave velocities along [100], [110] and [111] directions. The shear modulus, Young's modulus, Poisson's ratio, Lamé’s coefficients, average sound velocity and Debye temperature are estimated in the framework of the Voigt-Reuss-Hill approximation for ideal polycrystalline BaSnO₃ aggregate. Using the sX-LDA for the exchange-correlation potential, the calculated indirect fundamental band gap value is in very good agreement with the measured one. The analysis of the site-projected l-decomposed density of states, charge transfer and charge density shows that the bonding is of ionic nature. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the temperature effect on the lattice constant, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature is calculated.     

Structural, electronic, and optical properties of crystalline iodoform under high pressure: a first-principles study

The high pressure phases, electronic structure, and optical properties of iodoform at zero temperature have been investigated by first-principles pseudopotential plane-wave calculations based on the density-functional theory. A new high pressure polar monoclinic structure with space group Cc, denoted as β phase, has been observed after a series of simulated annealing and geometry optimizations. Our calculated enthalpies showed that the transition from α to β phase occurs at 40.1 GPa. Electronic structure calculated results showed that the insulator-metal transition in α phase due to band overlap is found at about 32 GPa. In addition, the calculated absorption spectra of iodoform are consistent with the experimental results.     

DFT study of the electronic, vibrational, and optical properties of SnO2

We report results on the electronic, vibrational, and optical properties of SnO₂ obtained using first-principles calculations performed within the density functional theory. All the calculated phonon frequencies, real and imaginary parts of complex dielectric function, the energy-loss spectrum, the refractive index, the extinction, and the absorption coefficients show good agreement with experimental results. Based on our calculations, the SnO₂ electron and hole effective masses were found to be strongly anisotropic. The lattice contribution to the low-frequency region of the SnO₂ dielectric function arising from optical phonons was also determined resulting the values of ? _1⊥ ^latt (0) = 14.6 and ? _1∥ ^latt (0) = 10.7 for directions perpendicular and parallel to the tetragonal c-axis, respectively. This is in excellent agreement with the available experimental data. After adding the electronic contribution to the lattice contribution, a total average value of ?₁(0) = 18.2 is predicted for the static permittivity constant of SnO₂.     

Structural, optical, and electronic properties of a series of 3,4-propylenedioxythiophene oligomers in neutral and various oxidation States

A series of 3,4-propylenedioxythiophene (ProDOT) oligomers (nP(Hex)) with dihexyl side chains and methylthio end-capping units was synthesized as a model of poly(3,4-alkylenedioxythiophene)s. The slope of the linear relationship between the energy of the absorption maxima of nP(Hex) in the neutral states and the reciprocal of the number of monomer units (1/n) was found to be comparable to that of 3,4-ethylenedioxythiophene (EDOT) oligomers, suggesting that both the ProDOT and the EDOT oligomers have a similar effective conjugation. In cyclic voltammetry measurements, both the first and second oxidation waves and the third and fourth waves were shown to merge into one peak with increasing chain length. The stepwise chemical oxidations of nP(Hex) with SbCl(5) in CH(2)Cl(2) at room temperature gave their stable cationic species in various oxidation states, and it was found that only the radical cations (polarons) have an obvious absorption band in the visible region. Interestingly, when the absorption spectra of tetramer radical cation 4P(Hex)(+·) were measured at low temperatures, reversible disproportionation into dication 4P(Hex)(2+) and neutral species 4P(Hex) was observed in addition to π-dimer formation. Furthermore, the radical cations of the longer oligomers showed only the disproportionation reaction. From the comparisons of the results of experiments and the theoretical calculations of the dications, 6P(Hex)(2+) was found to have a closed-shell nature, and only a weak singlet biradical character appeared even in longer oligomers 10P(Hex)(2+) and 12P(Hex)(2+). Overall, the electron-donating dioxy substituents are considered to stabilize high p-doping levels with closed-shell dication (bipolaron) structures in poly(3,4-alkylenedioxythiophene)s, which enables the transparency properties of the polymers.     

Growth format, electronic architecture, magnetic, and optical properties of aromatic cyclo-Cu3Au3 homotops

Bimetallic Cu(3)Au(3) clusters have been investigated using electronic structure calculation techniques (DFT) to understand their electronic, magnetic, and optical properties as well as the geometrical structures. The most stable homotop is the planar cyclo-[Cu(3)(micro-Au)(3)] form consisting of a triangular positively charged Cu(3) structural core with negatively charged Au atoms occupying exposed positions. This structure is characterized by the maximum number of heterobonds and peripheral positions of Au atoms. Possible growth formats of the cyclo-[Cu(3)(micro-Au)(3)] homotops have been explored following both the edge-capping and the stepwise metal atom substitution mechanism. The bonding pattern along with the density of states (DOS) plots of the cyclo-[Cu(3)(micro-Au)(3)] homotop are thoroughly analyzed and compared with those of the pure cyclo-[Cu(3)(micro-Cu)(3)] and cyclo-[Au(3)(micro-Au)(3)] clusters. Particular attention was paid on the stability of these bimetallic clusters in relation with the ring-shaped electron density distribution (aromaticity). It was found that all 3-membered metal rings exhibit significant aromatic character, which was verified by a number of established criteria of aromaticity, such as structural, energetic, magnetic (NICS profiles), and out-of-plane ring deformability criteria. The NICS (1) values correlate well with the out-of-plane ring deformation energy. Finally, a comprehensive analysis of the optical spectra of the CuAu, Cu(2), and Au(2) diatomics and the cyclo-[Cu(3)(micro-Au)(3)], cyclo-[Cu(3)(micro-Cu)(3)], and cyclo-[Au(3)(micro-Au)(3)] clusters placed the electronic assignments of the optical transitions on a firm footing.