Geometric and Electronic Behavior of C60 on PTCDA Hydrogen Bonded Network

Self-assembled supramolecular networks are promising spacer layer for electronic decoupling from the metal substrate.However,the mechanism behind of how the intrinsic electronic structure of spacer layers affects the adsorbate is still unclear.Here a hydrogen bonded network composed of n-type semiconducting molecules 3,4,9,10-perylene-tetracarboxylic-dianhydride(PTCDA)is prepared under ultra-high vacuum to serve as a spacer layer for functional organics C60 on Au(111).The geometric and electronic information of C60 was investigated by scanning tunneling microscopy and scanning tunneling spectroscopy(STM/STS)at 5 K.Effective decoupling from the metal surface yields an energy gap of 3.67 eV for C602nd,merely considering the HOMO-LUMO peak separation.The broadening of resonance peaks in STS measurements however indicates unneglected interlayer interactions in this hetero-organic system.Moreover,we scrutinize the nucleation sites of C60 on PTCDA layer and attribute this to the decreased diffusion capability on a less dense molecular arrangement possessing inhomogeneous spatial distribution of unoccupied molecular orbitals.     

Molecular docking,quantum chemical computational and vibrational studies on bicyclic heterocycle “6-nitro-2,3-dihydro-1,4-benzodioxine”: Anti-cancer agent

The heterocyclic aromatic compounds are primarily used to make pharmaceutical and agrochemicals. In addition, these compounds can be chosen as antioxidants, corrosion inhibitors, electro and opto-electronic devices, polymer material, dye stuff, developers, etc. On the account of this, the heterocyclic aromatic 6-nitro-2,3-dihydro-1,4-benzodioxine (6N3DB) was chosen and the structure is optimized to predict the important properties of it. The structural parameters such as bond length and bond angle have been obtained by DFT/B3LYP/6-311++G(d,p) basis set to know the geometry and orientation of 6N3DB. The molecule has been characterized by FT-IR and FT-Raman spectroscopic techniques to predict the functional groups, vibrational modes and aromatic nature of 6N3DB. The chemical shifts of ¹H and ¹³C have been obtained experimentally and compared with the theoretical data. The parameters such as the band gap between HOMO-LUMO orbitals, λ_max, and electron transition probability in frontier orbitals have been estimated to know the NLO and corrosion inhibition activity. HOMO-LUMO orbital diagram has been obtained for different energy levels and their band gap energies have been compared with UV–vis band gap values. The chemical significance of the molecule has been explained using ELF, LOL, and RDG. The binding energy and intermolecular energy values indicate that the title compound possesses anti-cancer property through hydrolase inhibition activity.     

BiVO4/TiO2 core-shell heterostructure: wide range optical absorption and enhanced photoelectrochemical and photocatalytic performance

In the present study, pristine BiVO₄, TiO₂ and BiVO₄/TiO₂ core-shell heterostructured nanoparticles are prepared by hydrothermal methods and studied for structural, morphological, optical, photoelectrochemical water splitting and photocatalytic degradation of methylene blue as an organic pollutant. Both pristine BiVO₄ and TiO₂ exhibit poor PEC and PC performance under visible light illumination. However, an enhanced PEC and PC activity in BiVO₄/TiO₂ core-shell heterostructure is observed due to high solar energy absorption and superior charge separation properties in core-shell nanoparticles. The photoelectrode prepared using BiVO₄/TiO₂ core-shell nanoparticles exhibit a photocathode behavior and produced cathodic photocurrent, however, the pristine BiVO₄ and TiO₂ photoelectrodes act as photoanode and produced anodic photocurrent. This behavior of change in current direction is also observe in the Mott-Schottky analysis where the BiVO₄/TiO₂ core-shell nanoparticles photoelectrode exhibits the positive slow showing p-type semiconducting behavior. The change in cathodic photoresponse in core-shell nanoparticles in comparison to anodic photoresponse of BiVO₄ and TiO₂ nanoparticles is explained in terms of the variations in the work function values. These results highlight the advantages of core-shell nanoparticle of suitable materials for photocatalytic and photoelectrochemical applications.     

Electronic transport properties of carbon chains between Au and Ag electrodes: A first-principles study

We report first-principles calculations of the current-voltage characteristic and the conductance of carbon-based molecular wires with different length capped with sulfur ends between two metallic electrodes made of different metals. The optimized molecular structure of carbon chain in the junction is presented on the structure of polyyne. The conductance of the polyyne wires shows oscillatory behavior depending on the number of carbon atoms (triple bonds). Current rectification is found and rectification direction presents inversion with the odd and even number of carbon atoms.     

The effect of crystal lattice distortions on the electronic band structure and optical properties of the N,V- and N,Na-doped anatase

The crystal structure, energy band structure and optical absorption of the N,V-doped and N,Na-doped anatase are studied by means of the first-principle pseudo-potential plane wave and linear muffin-tin orbitals methods. We show that the nitrogen and vanadium atoms have a tendency to form covalently bonded pairs. The crystal lattice distortions associated with doping essentially affect the optical absorption. With doping the impurity bands emerge in the band gap of the host anatase, however, a noticeable increase of optical absorption takes place at the energy only above 3 eV. Possible impact of this effect on the photocatalytic activity of the doped anatase is outlined.     

First-principles calculations on electronic structures of Fe-vacancy-codoped TiO2 anatase (1 0 1) surface

The electronic structures of Fe-doped TiO₂ anatase (1 0 1) surfaces have been investigated by all spin-polarized density functional theory (DFT) plane-wave pseudopotential method. The general gradient approximation (GGA)+U (Hubbard coefficient) method has been adopted to describe the exchange-correlation effects. Through the density functional calculations for the formation energies of various configurations, the complex of a substitutional Fe plus an O vacancy was found to form easily in the most range of O chemical potential. The calculated density of the states of the system of Fe-doped surface with a surface oxygen vacancy shows a band gap narrowing from 2.8 to 1.9 eV comparing with the pure surface due to the synergistic effects of surface Fe impurities with O vacancies. The system processes high visible light sensitivity and photocatalytic ability by decreasing extrinsic absorption energy. By comparing the partial DOS of some O and Ti atoms lying in the outermost and bottom layers of Fe-doped surfaces, it was found that the influence of Fe impurities on the electronic structure of the system is localized.     

Structural, elastic and electronic properties of a new ternary-layered Ti2SiN

The structural, elastic and electronic properties of Ti₂SiN were studied by first-principle calculations. The calculated bond lengths of Ti-Si and Ti-C are 2.65 and 2.09 Å, respectively. The results show Ti₂SiN is mechanically stable, and its bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio μ and anisotropy factor A are determined to be 182 GPa, 118 GPa, 291 GPa, 0.233 and 1.57, respectively. The calculated electronic structure indicates that Ti₂SiN is anisotropic and conductive.     

Investigation on densification of Al2O3/B4C ceramic by ab initio calculation and experiment

Compared to experiment, the adsorption energies, bonding properties, and electronic structure of two different Al₂O₃/B₄C bridge sites with seven different Al₂O₃ surfaces are investigated by ab initio periodic density functional theory. The Al₂O₃/B₄C ceramic sintered in Ar is synthesized and measured by XRD and TEM. The calculated results reveal that the densification of O_bridge site of Al₂O₃/B₄C surface is better than that of Al_bridge. The Al₂O₃ (1 1 3)/B₄C with O_bridge is the most favorable and stable. The electronic structure shows that the electron hybridization exists between Al, O atoms and C, B atoms. The results indicate that the calculated results are in good agreement with the experiment.     

Structural stabilities, electronic, elastic and optical properties of SrTe under pressure: A first-principles study

The structural, electronic, elastic and optical properties as well as phase transition under pressure of SrTe have been systematically investigated by first-principles pesudopotential calculations. Five possible phases of SrTe have been considered. Our results show that SrTe undergoes a phase transition from NaCl-type (B1) to CsCl-type (B2) structure at 10.9 GPa with a volume collapse of 9.43%, and no further transition is found. We find that SrTe prefer h-MgO instead of wurtzite (B4) structure for its metastable phase because that the ionic compound prefers a high coordination. The elastic moduli, energy band structures, real and imaginary parts of the dielectric functions have been calculated for all considered phases, and we find that a smaller energy gap yields a larger high-frequency dielectric constant. Our calculated results are discussed and compared with the available experimental and theoretical data.     

Electronic structure of EuPtSi3 studied from the first principles calculation

We investigate the electronic structure of EuPtSi₃ using full potential linearized augmented plane wave method within the generalized gradient approximation. We reproduce the observed easy axis of magnetization as well as magnetic moment and propose that the magnetic configuration for this compound is incommensurate or noncollinear. We find that the spin configuration has only negligible effect on the band around Fermi energy. EuPtSi₃ and its isostructural superconductor BaPtSi₃ have similar band structures. Despite the shorter Pt-Si bond, EuPtSi₃ possesses larger density of state near the Fermi energy compared with BaPtSi₃, thus the structural difference and the associated difference in band structure cannot explain the non-superconductivity of EuPtSi₃.