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Abstract In this paper, four types of compounds are considered: ideal wurtzite (B N), N vacancies in B N (B N − V N), A l doped ideal B N (A l : B N) and A l doped B N with N vacancies(A l : B N − V N). The structural, electronic and magnetic properties are calculated by using the density functional theory (DFT) based on the generalized gradient approximation implemented in Quantum-Espresso code. Our results show that the nitrogen vacancies and the aliminium impurities are responsible of the magnetic properties in these compounds. We have also found that aluminium impurities have a remarkable effect on the optical band gap. Our results are in good agreement with experimental and other theoretical studies. We can conclude from this study, that this material can be used as diluted magnetic semiconductors. Highlights • The DFT method has been used to study the Al doped (w−BN). • The lattice parameters increase with the incorporation of Al in the BN supercell. • The Al impurities decrease the value of the band gap. • Al and N vacancy induce magnetic properties. [ABSTRACT FROM AUTHOR]

This paper described a comprehensive DFT + U investigation on the general trends in structural stability, electronic and optical absorption properties, photocatalytic activity of BiOCl doped with 3 d transition metals (TMs = Sc, V, Cr, Ti, Fe, Co, Ni, Cu, Zn). We find that it is rather difficult for Sc, V, Ti, Ni atoms to substitute Bi into BiOCl crystal lattice in experiments due to their positive formation energies, but the negative formation energies for Cr-, Mn-, Fe-, Co-, Ni-, Cu-, Zn-doped BiOCl systems exhibit the thermodynamic structure stability. Most of TMs doping could narrow the band gap of BiOCl and lead to the changes in conduction band minimum and valance band maximum as well as the formation of several impurity energy levels within the forbidden band of BiOCl, achieving the photoactivity improvement and simultaneously maintaining the stronger redox potential. With 3 d TMs doping, the optical absorption intensity of BiOCl around 350 nm increased and exhibited a redshift to the different extents, in good agreement with reported experimental data. Our theoretical calculations should provide meaningful guidance for the experimentalists to design and develop more thermodynamically stable and highly effective visible light response photocatalysts. [ABSTRACT FROM AUTHOR]

In this paper, the carbon-doped boron nitride nanoplate (C-BNNP) was prepared by pyrolyzing the precursor under N 2 and served as an excellent adsorbent for removal of Rhodamine B (RhB). The structure and composition of C-BNNP were characterized and its adsorption behavior for RhB was investigated. Compared with boron nitride nanoplate (BNNP) which was synthesized under NH 3 , C-BNNP displayed an enhancement of the adsorption capacity for RhB (833 mg/g). The adsorption activity was comprehensibly studied by kinetics, isotherm and thermodynamics. The adsorption kinetics followed pseudo-second-order model. The equilibrium adsorption data agreed well with the Langmuir isotherm. And the thermodynamics indicated that the adsorption process was a spontaneous, exothermic and physisorption process. In addition, the density functional theory was proposed that doping carbon in the BNNP decreased the chemical hardness of the adsorbent and enhanced the adsorption capacity of C-BNNP for RhB. [ABSTRACT FROM AUTHOR]

In this paper, structural and electronic properties and stability of (10, 0) born nitride nanotube (BNNT) are considered within density functional theory by doping group IV elements of the periodic table. The HOMO-LUMO gap has been strongly modified and treated a dual manner by choosing B or N sites for dopant atoms. Formation energy calculation shows that B site doping is more stable than N site doping. Results also show that all dopants turn the pristine BNNT into a p-type semiconductor except for carbon-doped BNNT at B site. [ABSTRACT FROM AUTHOR]

• Systematic study of 3d transition metal-doped CNTs. • V(Cr, Mn, Co)-doped CNTs show spin-polarization effects. • The 3d transition metal doping makes a big difference to the energy band. • 3d transition metal doping increases the quantum capacitance. • Ni-CNT has the largest quantum capacitance near zero potential. Supercapacitors are valued as one of the new green energy storage devices, but the low energy density limits the wide application of supercapacitors. In this paper, the effects of 3d transition metal doped on electronic structure and quantum capacitance of carbon nanotubes are investigated using DFT. The calculations show that elemental doping has caused the break-up of two degenerate states near the Fermi level, quasi-local state changes in the energy band, and the creation of new energy bands. The doping of V(Cr, Mn, Co) causes spin polarization in the energy band. The change in energy band affects the density of states near the Fermi level, effectively increasing the quantum capacitance and surface charge density of the carbon nanotube electrode. The quantum capacitance of Ni-doped carbon nanotubes is the largest, at 59.74 µF/cm2. In the range of water stability, Ti(V, Gr, Mn, Co)-CNT are suitable for use as electrode materials in symmetrical double layer supercapacitors. Sc(Fe, Cu, Zn)-CNT is suitable for use as anode materials in asymmetric double layer supercapacitors. Ni-CNT is suitable for use as a cathode material for asymmetric double layer supercapacitors. This study verifies the feasibility of 3d transition metal doping to improve the quantum capacitance of carbon nanotube electrodes. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, the effects of Al doping and equibiaxial strain on monolayer h-BN were investigated by first-principles calculations. The results show that with tensile strain applied, the structure of the material is more stable, while the structural stability of the material decreases when compressive strain is applied. When the monolayer h-BN is doped with Al, the band gap decreases, and the higher the doped Al concentration, the lower the band gap. Equibiaxial strain is very effective for band gap tuning of monolayer h-BN. The optical calculation results show that the peaks of dielectric function and optical constant of the material decrease after Al doping, and the peaks decrease with the increase of Al concentration. When the strain is tensile, the optical properties of the material will be red-shifted as a whole, and the optical properties of the material will be blue-shifted when compressive strain is applied. After the monolayer h-BN was doped with two Al atoms and a strain of −9% was applied, the optical properties of the material were significantly affected. Our study provides some theoretical implications for the application of monolayer h-BN in the field of spintronic devices and optoelectronic devices. • The effect of equbiaxial strain and Al doping on monolayer h-BN were investigated. • Using first principles based on density functional theory. • Compared with the compression strain, the structure of the material is more stable under the tensile strain. • Band gap decreases with increasing Al doping concentration. • Optical properties of the material are red-shifted with tensile strain and blue-shifted with compressive strain. [ABSTRACT FROM AUTHOR]

Capable of achieving wide control over energy band gap and following optoelectronic properties; the highly mismatched alloys (HMAs) are considered to be promising materials for solar energy conversion devices. The dramatic restructuring of energy bands and density of states in HMAs caused by the replacement of anions with distinctly-mismatched isovalent constituents could further be an important course in improving their thermoelectric efficiency. In this paper, we attempt to explore and address the composition-induced modifications in the electronic band structure and the resultant effects on optical spectra and thermoelectric coefficients of GaN 1−x Sb x based HMAs in the framework of density functional theory. We observe, the substitution of N by Sb, considerably affects its band structure and split the conduction band minimum (CBM) into sub-bands. With increasing Sb composition, the lowest sub-band stemmed from N-s electrons has experienced drastic downward shift leading to energy gap narrowing. Interestingly, the energy gap narrowing along R- Γ is found to be faster than that of Γ- Γ point leading to an amazing direct to indirect band gap crossover. On the other hand, the composition-induced energy gap narrowing stimulates the red-shift in fundamental absorption edge in both ultraviolet and the infrared regime, making the GaNSb potentially useful material for photovoltaic applications. In addition, substantial effect on the thermoelectric coefficients of GaNSb is also observed via Sb substitution. We obtain larger Seebeck coefficient, improved power factors and figure of merit (ZT) for GaNSb at low Sb substitution and found diminishing effect with the further increase of Sb composition. With enhanced Seebeck coefficient, power factor and ZT values at modest doping levels, GaNSb alloy could be a promising candidate for near or above room temperature thermoelectric applications. [ABSTRACT FROM AUTHOR]

Boron nitride nanotubes (BNNTs) are semiconductors with a wide band gap. In comparison with carbon nanotubes (CNTs), BNNTs have higher chemical stability, excellent mechanical properties and higher thermal conductivity. In this paper, we study the effect of diameters and substituting B and N atoms of various zigzag BNNTs with Al, on structural and electronic properties of BNNTs in solid state using the density functional theory method. The results of calculations of density of states and band structure (band) showed that the band gap between the valence and conduction level increases as a result of the enhancement of tube diameter of BNNTs. Finally, the results showed that the electronic properties of the pristine BNNTs can be improved by doping Al atom in the zigzag configuration of tubes. [ABSTRACT FROM AUTHOR]

In this paper, spin-polarized density functional calculations on the structural, electronic, optical and magnetic properties of the zincblende structure of the and alloys at in the ferromagnetic (FM) ordering has been investigated. The study is accomplished using the full-potential (FP) linearized augmented plane wave plus local orbital (LAPWlo) self-consistent scheme of calculations. To incorporate the exchange correlation component in the total energy calculations of the crystal, Perdew-Burke and Ernzerhof (PBE) parameterization for the generalized gradient approximation (GGA) and GGA U are employed. Basically, for both alloys, to address their structural properties, we calculated their equilibrium lattice constants, bulk moduli as well as pressure derivatives. In general, from the analysis of the obtained electronic band structure of these alloys, the half-metallic nature of and nearly half-metallic nature of the alloy are demonstrated. The plotted density of states (DOS) curves project spin-exchange splitting energy and as generated by V-3 d states. It has been clearly evident that the effective potential results for the spin-down case are more striking than for the spin-up case. In order to describe the magnetic behavior of these alloys, the exchange constants (valence band) and (conduction band) as well as the magnetic moment values are estimated. The calculated results of the magnetic moment show that the main source in the reduction of the local magnetic moment of V in the alloys in comparison with its free value is a - orbital hybridization and partial transfer to nonmagnetic sites of (Zn, S) and (Cd, S) in and alloys. In addition, a study concerning optical properties, such as the refractive index, reflectivity and absorption coefficients is performed to determine their potential for optical and optoelectronic devices. [ABSTRACT FROM AUTHOR]

TiO 2 (titania) is one of the promising materials for photocatalytic applications. In this paper we report on recently obtained theoretical results for N and S doped, as well as N+S co-doped 6-layer (101) anatase nanotube (NT). First principles calculations in our study have been performed using a modified B3LYP hybrid exchange-correlation functional within density functional theory (DFT). Here we discuss the energy of defect formation mechanism and electronic band structure for nanotubes under study. We also report on influence of dopant concentration on the NT's band structure and discuss the defect–defect interactions. [ABSTRACT FROM AUTHOR]

To improve the photocatalytic activity of narrow-gap material Bi 2 O 3 , efforts need be made to lower the electron–hole recombination rate and widen the response range of visible light. Understanding the related mechanism is vital, which may lead to high electron-hole mobility and suitable band edge. In this paper we have studied the atomic and electronic structure of single metallic atom (Ag, Cu, Pb, Pd, Sn)-doped and nitrogen (N)-metal codoped Bi 2 O 3 with α phase by first principles calculations. The calculation results firstly show that new impurity states appeared in band gap of α -Bi 2 O 3 after single metal doping, especially for the doping of Cu, Ag and Pb, which showed shallow acceptor levels for α -Bi 2 O 3 . And the formation energy analysis indicates that Cu doped system was easier to be formed than other doped systems. All of those calculated properties are helpful to enhance the photocatalytic property of α -Bi 2 O 3 , which agrees well with experimental results. Interestingly, for anion atom N together with metallic atom (Ag, Cu, Pb, Pd, Sn) codoped α -Bi 2 O 3 systems, it is found that N-2p state had impact on the electronic structure. Holes were demonstrated to be more delocalized in (Cu + N) codoped α -Bi 2 O 3 system, which was responsible for high mobility of holes, then lowering the electron–hole recombination, and finally improving the photocatalytic performance of Bi 2 O 3 significantly. [ABSTRACT FROM AUTHOR]

In this paper, the heterofullerenes made of the smallest fullerene, C20were investigated by quantum chemistry calculations based on density functional theory. The geometrical structures, energies, electronic properties, and the aromaticities of the C19X (X = B, N, O, Al, Si, P, S, Ga, Ge, As, and Se) cages were studied systemically and compared with those of the pristine C20cage. It is found that the doped cages with different heteroatoms exhibit various structural, electronic, and aromatic properties. Several doping behaviors of the C19X cages are different from those of the C59X cages. These results imply the possibility to modulate the physical properties of heterofullerenes by tuning the sizes of the carbon cages as well as the substitution elements. [ABSTRACT FROM PUBLISHER]

The absorption edge shifted to long wavelength direction and short wavelength direction of two opposite experimental conclusions have been reported, when the band-gap and absorption spectra of -doped anatase 2 were studied. In order to solve this contradiction, the electronic structure and the optical property of heavy doped anatase 2 have been studied by the first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory with +U method modification. The calculated results indicate that the higher the -doping is, the higher the total energy is, the worse the stability is, the higher the formation energy is, the more difficult the doping is, the wider the optical band-gap is, the more obvious the absorption edge shifting to short wavelength direction is, the lower the absorptivity and the reflectivity is, which is in agreement with the experimental results. The reasonable interpretation of the contradiction has been reported in this paper, too. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the electronic structure and magnetic properties of K and Mn co-doped BaCd2As2 using density functional theory within the generalized gradient approximation (GGA) + U schemes. Calculations show that the ground state magnetic structure of Mn-doped BaCd2As2 is antiferromagnetic while K and Mn co-doped BaCd2As2 is ferromagnetic. Electronic structures indicate that the superexchange mechanism leads to the antiferromagnetic coupling between Mn atoms in Mn-doped BaCd2As2 while the hole-mediated Zener's p–d exchange mechanism leads to the ferromagnetic coupling between Mn atoms in K and Mn co-doped BaCd2As2. [ABSTRACT FROM AUTHOR]

Based on the first-principles plane wave ultra-soft pseudo potential (USP) method of density function theory pure and doped and - codoping anatase 2 supercell models were established, respectively, and calculated their energy in this paper. The calculated results show that the three doping systems compared to the pure anatase 2 band gap narrowed which results in red-shift of the optical absorption edges and - codoped anatase 2 have the most obvious visible effect. Meanwhile, synergy is very effective for the separation of electron-hole pairs and the electrons have a better lifespan. Research found that the trend of the donor's movements at the shallow level of - codoped anatase 2 is not obvious. This is due to its very thick shell, resulting in shielding effect of the outer layer of the -4f. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the structural, electronic and magnetic properties of Ga12N12 cluster doped with monodoped and bidoped atoms within the density functional theory (DFT). Substitutional, exohedral and endohedral doping are considered. It is observed that both monodoped and bidoped clusters tend to be in exohedral doping. Mulliken population analysis is performed to obtain the charge transfer and magnetic moment. The magnetic moment is mainly derived from 3d orbitals of atom for all isomers, while the magnetic properties would rely on the Fe-Fe distance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two phosphorescent Ir(III) complexes were synthesized and doped into a supporting matrix of bio-MOF-1 via cationic exchange. • Their phosphorescent emission was confirmed by density functional theory and emission lifetime, making them applicable for oxygen sensing. • Linear working curves were observed for both composite samples, showing sensitivity as high as 23.65 with response/recovery time of 9/22 s. • Humidity effect on sensing performance was limited. In this paper, two phosphorescent Ir(III) complexes, Ir(ppy) 2 (Ln), were synthesized using 2-phenyl pyridine (ppy) as the first (major) ligand and two phosphorous compounds (L1 and L2) as the auxiliary ligand. Their single crystal structure and electronic structure were discussed. Ir(ppy) 2 (Ln) complexes were doped into a supporting matrix of bio-MOF-1 via cationic exchange to ensure their uniform distribution. Their successful doping was confirmed by SEM, fluorescence microscopy image, XRD, N 2 adsorption/desorption and ICP measurement. Their photophysical parameters, including absorption spectra, excitation spectra, emission spectra, emission lifetime and quantum yield, were discussed in detail. Their phosphorescent emission was confirmed by density functional theory and emission lifetime, making them applicable for oxygen sensing. Linear working curves were observed for both composite samples, showing sensitivity as high as 23.65 with response/recovery time of 9/22 s. Humidity effect on sensing performance was limited. These parameters were found superior to literature ones based on phosphorescent Cu(I), RE(III), Ru(II) and Re(I) complexes. The sensing mechanism was revealed as a dynamic collision between Ir(ppy) 2 (Ln) and O 2 molecules. The novelty of this work was the combination of phosphorescent Ir(III) complexes with porous bio-MOF-1, resulting in greatly improved sensitivity and linear sensing with short response time. [ABSTRACT FROM AUTHOR]

This work reports an experimental and theoretical investigation of pure, Sr, and (Sr,Co) co-doped CdS systems. Pure and co-doped CdS nanostructure thin films were grown with varying Co doping concentrations by sol-gel spin coating method. X-ray diffractograms of the films reveal that the films grow along (002) plane and the crystallites sizes were about ∼3–6 nm. The band gaps of the films were obtained in order of 2.30–2.48 eV and a blue shift in the band gap with co-doping was observed in comparison with Sr:CdS system. In addition, pure and co-doped CdS system were also investigated via density functional theory. Initially, pure and co-doped CdS systems were optimized using WIEN2k software based on density functional theory. The calculated optical properties and band gap reveal a close agreement with the experimental results. The (Sr,Co) co-doped CdS shows the spin polarization effect on the valence band which makes this materials suitable for optoelectronics and spintronics applications. [ABSTRACT FROM AUTHOR]