Electron Density Contours Research Articles

Optical assessment of vertical TFET based on heterojunction of GaSb-Si

This paper investigates the electrical and opto-sensing analysis of hetero stack vertical TFETs based on III/V group Gallium antimonide (GaSb)-Si at various wavelengths within the visible spectrum. Initially, the drain current, energy band diagram, and electron density contour plot are extracted in order to study the DC and electrical behavior of the device. Following that, their performance is evaluated by altering the source side thickness and observe the tunneling rate of device. Furthermore, the photo application of the device is noticed by computing the critical optical parameter such as sensitivity (Sn), noise factor, and efficient characteristics. Finally, a comparative table is included to set the benchmark and highlight the importance of hetero stack TFET. The device's maximum reported sensitivity is approximately 25.2 and responsivity (R) is 0.8 A/Watt at 320 nm wavelength. Additionally, we examined the effect of trap charges under light state at the gate-channel, isolator-channel, and source-channel interface respectively.

Intramolecular Repulsion Visible Through the Electrostatic Potential in Disulfides: Analysis via Varying Iso-density Envelopes.

For a series of diethyl disulfide conformations, the nearly touching contours of the electrostatic potential plotted on iso-density molecular surfaces allow the assessment of intramolecular repulsion. The electrostatic potential is plotted on varying iso-density envelopes to find the nearly touching contours for which (a) the surface electrostatic potential does not show overlap between atoms or functional groups and (b) the typical features are visible (σ-hole, lone pair, hydrogen VS,max). When these nearly touching contours X are closer to the nuclei, the more electron density is excluded from the iso-density envelopes and the smaller are the volumes corresponding to these envelopes. Both the contours X and the corresponding volumes are found to correlate with relative conformational energy, reflecting the degree of intramolecular repulsion present in the various diethyl disulfides. Quantitative estimates of intramolecular repulsion can be made based on relationships between the nearly touching contour X vs relative energy and volume (of the nearly touching contour X) vs relative energy, obtained for series of diethyl disulfide conformers. These relations were used to analyze intramolecular repulsion in a set of disulfides broader than diethyl disulfide conformers. We have shown that the approach of varying electronic density contours can be used in the study of repulsive intramolecular interactions, hereby extending earlier work involving attractive intermolecular interactions.

Ab-initio investigation of structural, opto-electronic, and thermodynamic properties of ZnAl2Se4 for photovoltaic applications

In this manuscript, the structural, opto-electronic, and thermodynamic properties of ZnAl2Se4 chalcogenide compounds were studied in detail using the full potential linearized augmented plane wave method. The exchange and correlation potentials used in density functional theory were calculated using local density approximation, the generalized gradient approximation (GGA) method, and the modified Becke–Johnson (mBJ) potential using Wien2k code. The obtained results were compared with each other as well as with available experimental data. At ambient conditions, ZnAl2Se4 is a direct wide bandgap (Г–Г) semiconductor with a bandgap of 2.1 and 3.3 eV with GGA and mBJ potentials, respectively. Density of states (DOS; total DOS and Partial Density Of States (PDOS)) and electron density contour plots were in similar accordance with bandgap, showing semiconductive behavior and covalent bonding nature. The optical properties like the real and imaginary parts of the dielectric constant, the energy loss function L( ω), and the conductivity σ( ω) were calculated. Optical aspects show interaction among phonon and electron in terms of long-range and short-range forces. The studied compound is very useful for various linear–nonlinear optical devices, so this compound is very valuable for several linear–nonlinear optical devices. So this manuscript represents a comprehensive approach for calculating the complete set of useful properties of the ZnAl2Se4 compound, which can provide support for understanding various device phenomena such as electrochemical sensing, photovoltaics, and nonvolatile electronic memories.

Physical properties of elastically and thermodynamically stable magnetic AcXO3 (X = Cr, Fe) perovskite oxides: a DFT investigation

Spin-polarized calculations of mechanical, electronic structure, phonon, optical and magnetic properties of AcXO3 (X = Cr, Fe) perovskite oxides (POs) has been computed using the full-potential linearized augmented plane wave method. The modified Becke Johnson (mBJ) approximation has been utilized for exchange-correlation potential and implemented in the WIEN2k code. The negative values of formation energy and the positive fRequencies of the phonon modes show the stability of studied perovskite oxides. The mechanical stability is confirmed through the elastic parameters such as shear modulus (G), Bulk modulus (B), Poisson ratio (ν) and Cauchy pressure. The semiconductor nature with an indirect bandgap is observed for both compounds in both spin channels. The computed electron density contour plot describes the bonding nature of both compounds. The magnetic moments are calculated, which show the major involvement of Fe and Cr atoms in the overall magnetism of studied compounds. The optical response is also evaluated, showing the maximum absorption in the ultraviolet region. The overall analysis of the calculated properties shows that the studied oxide perovskites are suitable for spintronic and optoelectronic applications.

Cooperativity and intermolecular hydrogen bonding in donor‐acceptor complexes of phenol and polyhydroxybenzenes

AbstractCooperativity between intermolecular and intramolecular hydrogen bonds is an important factor determining the strength of donor‐acceptor complexes. Its impact in poly‐1,2‐diols, notably polyhydroxybenzenes, is subject to debate. Density functional theory calculations have been performed on complexes of phenol, catechol, pyrogallol and 1,2,3,4‐tetrahydroxybenzene with pyridine, trimethylamine and trimethylphosphine oxide. Binding energies, proton NMR shifts, Quantum Theory of Atoms in Molecules analysis and Interacting Quantum Atoms (IQA) interaction energies reveal a positive cooperative effect of a topological intramolecular hydrogen bond (IMHB) in catechol relative to phenol, with insignificant or small negative effects of further HO groups. Except for catechol complexes, there are no topological IMHBs in any donors or their complexes, although all show Non‐Covalent Interaction isosurfaces. The absence of a topological IMBH in catechol itself is explained by electron density contour plots. Complexes of Me3N and Me3PO with catechol, pyrogallol and 1,2,3,4‐tetrahydroxybenzene display additional intermolecular hydrogen bonds, C‐H…H‐C and C‐H…O=P, respectively, with the hydrogen atom ortho to the bound HO group. The predominantly covalent or electrostatic character of the various hydrogen bond types is discussed in terms of the IQA energy partition scheme, which is also useful for characterising IMHBs in the absence of a bond critical point. These results further our understanding of the nature and the limits of cooperative hydrogen bonding in donor‐acceptor complexes.

Consequences of Overfitting the van der Waals Radii of Ions.

Atomic radii play important roles in scientific research. The covalent radii of atoms, ionic radii of ions, and van der Waals (VDW) radii of neutral atoms can all be derived from crystal structures. However, the VDW radii of ions are a challenge to determine because the atomic distances in crystal structures were determined by a combination of VDW interactions and electrostatic interactions, making it unclear how to define the VDW sphere of ions in such an environment. In the present study, we found that VDW radii, which were determined based on the 0.0015 au electron density contour through a wavefunction analysis on atoms, have excellent agreement with the VDW radii of noble-gas atoms determined experimentally. Based on this criterion, we calculated the VDW radii for various atomic ions across the periodic table, providing a systematic set of VDW radii of ions. Previously we have shown that the 12-6 Lennard-Jones nonbonded model could not simultaneously reproduce the hydration free energy (HFE) and ion-oxygen distance (IOD) for an atomic ion when its charge is +2 or higher. Because of this, we developed the 12-6-4 model to reproduce both properties at the same time by explicitly considering the ion-induced dipole interactions. However, recent studies showed it was possible to use the 12-6 model to simulate both properties simultaneously when an ion has the Rmin/2 parameter (i.e., the VDW radius) close to the Shannon ionic radius. In the present study, we show that such a "success" is due to an unphysical overfitting, as the VDW radius of an ion should be significantly larger than its ionic radius. Through molecular dynamics simulations, we show that such overfitting causes significant issues when transferring the parameters from ion-water systems to ion-ligand and metalloprotein systems. In comparison, the 12-6-4 model shows significant improvement in comparison to the overfitted 12-6 model, showing excellent transferability across different systems. In summary, although both the 12-6-4 and 12-6 models could reproduce HFE and IOD for an ion, the 12-6-4 model accomplishes such a task based on the consideration of the physics involved, while the 12-6 model accomplishes this through overfitting, which brings significant transferability issues when simulating other systems. Hence, we strongly recommend the use of the 12-6-4 model (or even more sophisticated models) instead of overfitted 12-6 models when simulating complex systems such as metalloproteins.

Improved optical performance in near visible light detection photosensor based on TFET

This paper presents the performance comparison of Si-based, Ge-source, and Heterogate (HG) TFET photosensor under visible range of spectrum using TCAD simulator. The optical generation rate, energy band diagram, Band to Band Tunneling rate, and electron density contour have been plotted for TFET based sensor under both light and dark regimes to investigate their optical behavior. Furthermore, spectral sensitivity (Sn) graph is extracted as a function of wavelength (λ) and gate voltage (Vgs) for these photosensors. Due to increased tunneling rate of optically produced carrier along the channel, the Sn of HG-TFET photosensor is found higher compared to Ge source and Si-based TFET photosensors. The Signal to Noise Ratio (SNR), Responsivity (R), and quantum efficiency (η) are reported to examine the performance of these photosensors in more elaborately. It is seen that the HG-TFET photosensor exhibits a better noise immunity and Responsivity rate relative to other simulated photosensing device. Finally, the various performance metrics of these photosensors are compared in tabular form. It is found that HG-TFET based photosensor has superior optical performance and its performance is further analyzed using Ge source or HfO2 as gate dielectric material.

Understanding of benzimidazole based ionic liquid as an efficient corrosion inhibitor for carbon steel: Experimental and theoretical studies

This work is focused on corrosion inhibition of N,N’-bis(carboxilic methyl)benzimidazolium based ionic liquid (IL) for carbon steel. Electrochemical polarization Tafel lines are nearly constant, generating H2 at electrode (M + HCl → Mn+ + H2 + Cl); however, the reaction has been largely inhibited by Imidazole (IMD), Benzimidazole (BMD) and N,N’-bis(carboxilic methyl) benzimidazolium catio (IL) since the blank current density (3.86 × 10-3 A/cm2) was reduced significantly to 1.95 × 10-5 A/cm2 for IL (5.0 mM), following as IMD (∼50%) < BMD (∼80%) < IL (∼95%). In impedance spectroscopy, the solution resistance (Rsol, 20 Ω-cm2 for blank) was increased to 23.54 Ω-cm2 for IMD, 23.6 for BMD and 28.43 Ω-cm2 for IL since the loop diameter was augmented greatly if the IL concentration was increased. A greater charge transfer resistance (Rct, 831.1 Ω-cm2) was obtained for IL at 0.5 mM as compared to IMD (134.8 Ω-cm2) and BMD (127.2 Ω-cm2), reaching a maximum of 1347 Ω-cm2. The corrosion inhibition of IL on the electrode was analyzed by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Energy Dispersive X-ray spectrometer (EDS), revealing that the corrosion-holes caused by HCl were covered neatly by IL, consisting with the EDS as Fe (60.2 %, O 22.9% for blank) was improved to 76.0, 80.5, and 87.3% %, for IMD and BMD and IL, respectively. The interaction of IL with iron surface was studied theoretically, observing the delocalization of imidazoline in IL, corroborating with Natural Transition Orbitals (NTOs), Electron density contour, molecular orbital and Density of Sates (DOS) studies.

Experimental and theoretical analysis of simultaneous removal of methylene blue and tetracycline using boron nitride nanosheets as adsorbent

The adsorption behaviour of boron nitride nanosheets (BNNSs) for the removal of methylene blue (MB) dye and tetracycline (TC) antibiotic from aqueous solution has been reported in this study. BNNSs were synthesized using a bottom-up technique with boric acid and urea as precursors. The synthesized material was characterized using high-resolution transmission electron microscopy, field emission scanning electron microscopy, atomic force microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy for morphological and structural analysis. Through kinetic studies, it was revealed that the pseudo-second-order model was obeyed by both MB and TC. The isotherm study showed that the adsorption was followed by the Langmuir model for the mixture of MB and TC, indicating that monolayer adsorption was preferred on the adsorbent. The BNNSs adsorbent could remove the mixture of MB and TC, and a maximum adsorption capacity of 322.5 mg/g was found. Further, it was easily separable and exhibited regeneration properties. The simultaneous adsorption characteristics of MB and TC on the surface of BNNSs has been investigated through the density functional theory (DFT) calculations to explore the adsorbing capabilities of BNNSs. This analysis investigates electrostatic potential, atomic charge distribution, electron density contour, and electron localization function projection. The current study demonstrates the sensing potential of BNNSs for adsorption of both MB and TC, simultaneously since the gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), i.e., HLG decreased to 1.54 eV. Further, chemical activity, electrical conductivity is quite high in the adsorption process. Also, negative charge transfer from the contaminant to BNNS takes place. The adsorption energy for MB-BNNS, TC-BNNS and MB+TC-BNNS were calculated to be − 117 kJ mol-1, − 1055 kJ mol-1, and − 844 kJ mol-1, respectively. These theoretical and experimental results show the promise of BNNSs as adsorbents for simultaneous adsorption of dyes and antibiotics from contaminated wastewater.

A Quantum Mechanical Viewpoint on Structural Stability of the Smallest Hydrated Sulfate Cluster [SO4(H2O)3]2-

Being the most kosmotropic type anion, SO 4 2 - shows a very strong affinity towards sequential hydration, and hence undergoes immediate stabilization via differently sized hydrated clusters [SO 4 (H 2 O) n ] 2− , n ≤ 80 in solution state. Interestingly, the smallest yet stable hydrated cluster detected through the advanced experimental techniques is [SO 4 (H 2 O) 3 ] 2− with hydration number n = 3. Despite its ubiquity in many sulfate enriched aqueous systems, the concerned electronic structure and structural stability reported so far are mostly based on the position of atomic nuclei in the theoretically produced low energy molecular geometry, which is, however, not regarded as a quantitative approach for depicting chemical bonding and structural entity in respect to electron density distributions around atoms and bonds between the atoms. In this study, the molecular orbitals (MOs) and Mulliken population analysis methods are used to extract chemical bond related information of [SO 4 (H 2 O) 3 ] 2− from its DFT derived molecular wavefunctions ( ) and then total molecular electron density surface (TMEDS), MOs iso-surfaces, and contour lines are deeply analyzed prior to describe how these EDSs actually provide detailed insights into the orbital interactions, atomic bonding, and structural stability. It is found that [SO 4 (H 2 O) 3 ] 2− ion stabilizes with (a) a closed 3D structural entity and a realistic distribution of electron cloud around the specific atoms and bonds, (b) a delocalized type electron density, and (c) an orbital type bonding interaction between the atoms. Besides these, a quantitatively measured electron amplitudes and the specific type bonding interactions make that hydrated structure quantum mechanically feasible.

A critical evaluation of [ML(ONO)]n+ (M = Fe, Ru, Os) as nitric oxide precursor influenced by spin multiplicity and geometrical parameters (M-O-NO and MO-N-O) for the NO release: A theoretical study

In cell biology, the physiological functions control blood pressure by the production of nitric oxide, and the exploitation of metal complexes such as [ML-ONO] (M = Fe2+, Ru2+, Os2+) has been motivated to study the photolytic liability of NO. The structural and electronic properties of the complexes of 1,4,8,11-tetrakis-(1-methyl-pyridyl)-1,4,8,11-tetraazacyclotetradecane were analyzed theoretically. The results show that β-cleavage of nitrito group in the complex [ML-ONO]n+ (M = Fe, Ru, Os; n = 1 or 2) favors the NO release, and observed the role of spin multiplicity. The M(II)-O-NO angle is associated with the degree of activation of the M(II)O—NO bond, relying on the excitations (S = 1 or S = 2), and it is corelated to the reduction of the bond angle ONO (~133° at S = 0) to ~ 105° at S = 1 or 2, favoring the nitrito β-cleavage for the complexes. This is consistent with orbital energy (dx2-y2) stabilizing the axial M(III)-O bond greater than that in M(II)-O [Fe < Ru ~ Os] as the excitation of singlet to triplet or to quintet prompts the NO delivery according to Gibbs free energy, agreeing with the transition state energy. However, at high spin state like 3/2 or 5/2, irrespective of bond angle M(III)-O-NO or ONO, the bond O-NO was broken spontaneously, resulting relatively a greater bond distance. Natural Transition Orbitals (NTOs), Molecular orbital (MO) Electron density contour on molecular orbital surface were also studied to understand the M-ONO bonding nature, and observed its performance in the TD-DFT electronic spectra.

Influence of Ternary and Quaternary Inclusion on Bandgap Tuning of CaTe: Prediction of Potential Thermoelectric Materials

The structural, optoelectronic, and thermoelectric properties of CaTe, Ca0.5Ba0.5Te, CaTe0.5Se0.5, and Ca0.5Ba0.5Te0.5Se0.5 alloys are studied using the full-potential linearized augmented plane wave method within the framework of density functional theory. The calculated ground-state properties agree well with available data. The electronic and bonding behavior of the materials is studied and further verified by electron density contours. Additionally, mechanical stability is confirmed by calculating the shear modulus, Young’s modulus, bulk modulus, and hardness values. From the brittle/ductile analysis, the newly predicted compounds are found to be less brittle (more ductile) than the parent CaTe compound. The valence band maxima and the conduction band minima (CBM) of the Ca0.5Ba0.5Te, CaTe0.5Se0.5, and Ca0.5Ba0.5Te0.5Se0.5 alloys are located at the Г point, resulting in a direct bandgap. The optical properties of the materials are calculated for the energy range of 0–13.5 eV. As expected, the highest Seebeck coefficient value is observed as 245.8 μV/K and 248.6 μV/K for CaTe0.5Se0.5 and Ca0.5Ba0.5Te0.5Se0.5 alloys, respectively, at 300 K. The present work exhibits the optoelectronic and thermoelectric properties, but the available material flexibility has various other applications.

DSMC modeling of rarefied ionization reactions and applications to hypervelocity spacecraft reentry flows

The DSMC modeling is developed to simulate three-dimensional (3D) rarefied ionization flows and numerically forecast the communication blackout around spacecraft during hypervelocity reentry. A new weighting factor scheme for rare species is introduced, whose key point is to modify the corresponding chemical reaction coefficients involving electrons, meanwhile reproduce the rare species in resultants and preserve/delete common species in reactants according to the weighting factors. The resulting DSMC method is highly efficient in simulating weakly inhomogeneous flows including the Couette shear flow and controlling statistical fluctuation with high resolution. The accurate reliability of the present DSMC modeling is also validated by the comparison with a series of experimental measurements of the Shenzhou reentry capsule tested in a low-density wind tunnel from the HAI of CARDC. The obtained electron number density distribution for the RAM-C II vehicle agrees well with the flight experiment data, while the electron density contours for the Stardust hypervelocity reentry match the reference data completely. In addition, the present 3D DSMC algorithm can capture distribution of the electron, N+ and O+ number densities better than the axis-symmetric DSMC model. The introduction of rare species weighting factor scheme can significantly improve the smoothness of the number density contours of rare species, especially for that of electron in weak ionization case, while it has negligible effect on the macroscopic flow parameters. The ionization characteristics of the Chinese lunar capsule reentry process are numerically analyzed and forecasted in the rarefied transitional flow regime at the flying altitudes between 80 and 97 km, and the simulations predict communication blackout altitudes which are in good agreement with the actual reentry flight data. For the spacecraft reentry with hypervelocity larger than the second cosmic speed, it is forecasted and verified by the present DSMC modeling that ionization reactions will cover the windward capsule surface, leading to reentry communication blackout, and the communication interruption must be considered in the communication design during reentry in rarefied flow regimes.

Investigations of structural, electronic and optical properties of YInO3 (Y = Rb, Cs, Fr) perovskite oxides using mBJ approximation for optoelectronic applications: A first principles study

The structural, electronic and optical properties of indium based novel combinations of ternary perovskite oxides YInO3 (Y = Rb, Cs, Fr) are investigated by first Principles DFT-based calculations scheme via Full Potential Linearly Augmented Plane Wave (FP-LAPW) technique. Comprehensive study is done among three cations (Rb, Cs, Fr) in the same order of symmetry in ABO3 cubical phase. Electronic properties are improved through PBE plus Tran and Blaha modified Becke-Johnson (PBE + TB-mBJ) functional. Using PBE-GGA, indirect band gaps are calculated to be 2.38 eV, 1.92 eV for RbInO3 and CsInO3, respectively. Whereas, FrInO3 exhibits direct band gap of 1.82 eV. However, these band gap values show improvement in all cases by the use of PBE + TB-mBJ functional. The phonon dispersion curves exhibit no imaginary phonon frequencies indicating that the studied compounds are structurally and dynamically stable. TDOS and PDOS results show the highest contribution of Fr-7s and In-5p states of FrInO3 in increasing conductivity. The electronic charge density contours depict covalent character between In ̶ O atoms. Whereas, spherical contours around the cations (Rb, Cs, Fr) show their ionic bonding. The optical analysis illustrates that the studied compounds possess conductivity and absorptivity in a wide range of the incident photon energies with their minimal reflectivity. The overall analyses depict that the considered compounds are potential candidates for applications in optoelectronic and other allied devices.

Height Variation of Gaps in 150‐km Echoes and Whole Atmosphere Community Climate Model Electron Densities Suggest Link to Upper Hybrid Resonance

AbstractRadar echoes from the daytime lower region near the magnetic equator, so‐called 150‐km echoes, have been puzzling researchers for decades. Neither the mechanisms that generate the enhanced backscatter at very high frequencies (typically 30–50 MHz), the sharp lower cutoff height, the intricate layering with multiple echo layers separated by narrow gaps, nor the modulation of the echoes by short‐period gravity waves is well understood. Here we focus on the diurnal variation of the echo layers—specifically, certain wide gaps in the vertical structure—which apparently descend in the morning, reach their lowest altitude near local noon, and ascend in the afternoon, sometimes described as necklace structure based on the appearance of the layers in range‐time‐intensity diagrams. Analyzing high‐resolution data obtained with the Jicamarca radar between 2005 and 2017, spanning more than one solar cycle, we find that (a) wide gaps and narrow lines occur in vertically stacked, systematically repeating pattern; (b) the gap heights vary with season and solar cycle; and (c) the gap heights can be associated with specific contours of plasma frequencies or electron densities. The last two findings are supported by simultaneous observations of VIPIR ionosonde reflection heights and by comparison of gap heights with electron density contours obtained with the WACCM‐X 2.0 global model. Finally, the wide gaps appear to coincide with the double resonance condition, where the upper hybrid frequency equals integer multiples of the electron gyrofrequency. This may explain why field‐aligned plasma irregularities are suppressed and enhanced radar backscatter is not observed inside the gaps.

Influence of strain and substitution on magnetocrystalline anisotropy of R2Fe14B (R=Pr, Dy and Y)

Abstract The intermetallic rare earth-transition metal ( R - T ) compound Nd 2 Fe 14 B has a large energy density and is an industrially important permanent magnet material. Its low Curie Temperature ( T C ) though limits its use for electric motor applications. To improve its high temperature permanent magnetic properties, the coercive field ( H C ) should be enhanced, which can be achieved by influencing intrinsic atomistic properties such as saturation magnetization ( M S ) and magnetocrystalline anisotropy energy (MAE). Strain effects and substitution are two important methods for influencing M S and MAE. Using numerical methods based on density functional theory, firstly M S and MAE of three R 2 Fe 14 B compounds with R = P r , D y and Y are calculated at 0 K. Further, the influence of changing the lattice parameter ratio c / a on MAE is studied. For increasing c / a , MAE of Y 2 F e 14 B and Pr 2 F e 14 B remains nearly constant, while MAE of Dy 2 F e 14 B decreases monotonously, up to 40 % per 1 % change in c / a . In the next step, 50 % of the R - atoms are substituted. For Pr 2 F e 14 B , MAE decreases with substitution of Dy and Y ; for Dy 2 F e 14 B it increases with Pr but decreases with Y ; for Y 2 F e 14 B it increases with Pr and Dy . The nucleation field ( H N ) of the substituted phases are estimated for different microstructures and visually compared to the non-substituted compounds, showing a large H N for P r D y F e 14 B . Further, based on DOS plots of the Y - D y F e 14 B system, the contribution of different atoms and atomic sites to MAE is discussed, and by visualizing the electronic density contours, the influence of substitution on Fe - atoms in Dy 2 F e 14 B and D y Y F e 14 B is studied.

Structure and Optical Properties of ZnO and ZnO&lt;sub&gt;2&lt;/sub&gt; Nanoparticles

Zinc oxide (ZnO) and Zinc peroxide (ZnO2) nanoparticles were synthesized by colloidal method at low temperature. The thermal stability of ZnO2 was studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-Ray diffraction (XRD). The crystalline structure and phase change from ZnO2 to ZnO by heat treatment was studied in detail. Morphology and particle size was examined using Transmission Electron Microscopy (TEM), for as synthesized ZnO and ZnO2 the shape of particles were cuasi-spherical for both materials with average size of 10±2.2 nm and 2.5±0.4 nm, respectively; The crystal size for ZnO obtained by heat treatment was 8±2.2 nm. Electron density contours show the chemical bond type ionic and covalent for ZnO and ZnO2. The vibrational properties were analyzed by Raman and IR spectroscopy. Band gap values were obtained from ultraviolet-visible (UV-Vis) absorbance spectrum. Photoluminescence (PL) spectrum for ZnO shows two emission edges located at 445 and 492 nm and in the case of ZnO2 presents one edge at 364 nm originated from the band edge emission. The optical spectra present a hypsochromic shift, compared with some reported in the literature.

Electronegativity-a perspective.

Electronegativity is a very useful concept but it is not a physical observable; it cannot be determined experimentally. Most practicing chemists view it as the electron-attracting power of an atom in a molecule. Various formulations of electronegativity have been proposed on this basis, and predictions made using different formulations generally agree reasonably well with each other and with chemical experience. A quite different approach, loosely linked to density functional theory, is based on a ground-state free atom or molecule, and equates electronegativity to the negative of an electronic chemical potential. A problem that is encountered with this approach is the differentiation of a noncontinuous function. We show that this approach leads to some results that are not chemically valid. A formulation of atomic electronegativity that does prove to be effective is to express it as the average local ionization energy on an outer contour of the atom's electronic density.

Structure, bonding, stability, electronic, thermodynamic and thermoelectric properties of six different phases of indium nitride

Density functional investigation is carried out on the structure and bonding, stability, electronic, thermodynamic and thermoelectric properties on the six different phases of indium nitride. In addition to the monolayer hexagonal, zinc blende, wurtzite and rock salt, two more new possible phases, viz. caesium chloride and nickel arsenide, are also explored. The calculated crystal parameters for all six phases are compared with available experimental and theoretical values. Band structure and density of states are predicted for understanding their behaviour in metal–insulator–semiconductor domains as well as the contribution of their different atomic orbitals around the valence and conduction band edges. Phonon dispersion curves are generated to understand the dynamical stability of the considered indium nitride phases. Further, a detail comparative study is performed on various thermodynamic and thermoelectric properties of the dynamically stable indium nitride phases. An electron density contour is also generated for the stable phases to understand the nature bonding between indium and nitride in those phases.

Tuning of electronic band gaps and optoelectronic properties of binary strontium chalcogenides by means of doping of magnesium atom(s)- a first principles based theoretical initiative with mBJ, B3LYP and WC-GGA functionals

First principle based theoretical initiative is taken to tune the optoelectronic properties of binary strontium chalcogenide semiconductors by doping magnesium atom(s) into their rock-salt unit cells at specific concentrations x = 0.0, 0.25, 0.50, 0.75 and 1.0 and such tuning is established by studying structural, electronic and optical properties of designed binary compounds and ternary alloys employing WC-GGA, B3LYP and mBJ exchange-correlation functionals. Band structure of each compound is constructed and respective band gaps under all the potential schemes are measured. The band gap bowing and its microscopic origin are calculated using quadratic fit and Zunger's approach, respectively. The atomic and orbital origins of electronic states in the band structure of any compound are explored from its density of states. The nature of chemical bonds between the constituent atoms in each compound is explored from the valence electron density contour plots. Optical properties of any specimen are explored from the computed spectra of its dielectric function, refractive index, extinction coefficient, normal incidence reflectivity, optical conductivity optical absorption and energy loss function. Several calculated results are compared with available experimental and earlier theoretical data.