Electronegativity Model Research Articles

Engineering the p-n switch: Mastering intrinsic point defects in Sb2Te3-dominant alloys

V2VI3-based alloys have long been established as the sole commercial material system for solid-state cooling. However, the volatility of the Se element in conventional n-type Bi2Te3-xSex leads to inconsistent reproducibility across production batches. Here, we unveil an innovative, highly reproducible n-type Bi0.5Sb1.5Te3 alloy, realized through strategic manipulation of native point defect. The initial Bi0.5Sb1.5Te3 is saturated with antisite defects, imbuing it with pronounced p-type conductivity. Our investigation, underpinned by the electronegativity and atomic size model and validated through density functional theory calculation, reveals that the replacement of Sb by In in the Bi0.5Sb1.5-xInxTe3 system effectively elevates the formation energy of negatively charged antisite defect, while simultaneously diminishing that of positively charged anion vacancy. This alteration in the dominant point defect type catalyzes a p-n type transition, prominently observed at around x = 0.15. We believe this constitutes the inaugural disclosure of a n-type Sb2Te3-rich bulk material. The observed low zT ∼ 0.16 at 360 K in n-type Bi0.5Sb1.05In0.45Te3, attributed to low electron mobility, is a focal point for ongoing performance enhancement efforts. These results not only enrich the comprehension of intrinsic point defect manipulation in the V2VI3 system, but also pave the way for the systematic evolution and realization of innovative, high-efficiency, and consistently reproducible n-type Bi2-xSbxTe3 alloys.

MODELOS E ELETRONEGATIVIDADE: UMA PROPOSTA DE SEQUÊNCIA DIDÁTICA PARA O ENSINO DE QUÍMICA

MODELS AND ELECTRONEGATIVITY: A PROPOSAL OF DIDACTIC SEQUENCE FOR CHEMISTRY TEACHING. Electronegativity is a useful chemical bonding property related to determining the polarity of molecules and formation of partial charges. In the 1930s, Linus Pauling studied the differences between theoretical and experimental binding energy values when he established that ionic contributions in covalent bonds were pertinent to elucidate these differences. The association of the nature of the elements present in the chemical bond with the discordance of results led to the quantitative determination of electronegativity, creating the first scale of this property. In addition, other scales were developed, such as by Robert Mulliken (1934), Albert Allred and Eugene Rochow (1958) and Leland Allen (1989). Although present in undergraduate Chemistry courses, the teaching of electronegativity is little explored in the literature and treated in a fragmented way in many materials. In this way, a didactic sequence is proposed for the approach of electronegativity and the scales designed by Pauling, Mulliken, Allred, Rochow and Allen directed to the first year of undergraduate in Chemistry. For a dynamic study of electronegativity models along with historical basement, modelling-based teaching is used so that students can assess scope, limitations and be able to participate in the creation of a model.

Stability of lithium boron carbides with defective chains and a new phase from strain-induced phase transition

The new chain structures of the main o-LiB13C2 crystal with (C-B-C) chain are proposed to obtain new structures. The structural, mechanical, electronic, and dynamic properties of the newly designed structures with the B12(X-Y-X) and B12(X-X) (X and Y = B, C, and N) formulae are investigated by the first principles of density functional theory (DFT), and detailed comparisons with the main crystal between the stable and unstable structures are given. It is found that the structures with (N-C-N), (C-Va-C), and (N-Va-N) chains meet the thermodynamic, mechanical, and dynamic stability conditions. The tensile strengths of the stable structures are examined, and it is observed that the (N-C-N) chain system underwent a phase change and turned into a new stable structure that has an (N-Li-N) chain and different bonding geometry and characteristics in interstitial space between the B12 icosahedra. A detailed geometry analysis utilizing the selected bond lengths, volume and surface area of B12 icosahedron is offered. The partial density of states, charge and critical point analysis, electron density differences are presented to clarify the bonding situations of the structures. The Bader charges of B12 icosahedra in the stable structures have positive, in contrast to Wade’s rule. The existence of the chain in the B12(X-Y-X) and B12(X-X) compounds affects the charging behavior of B12 icosahedron due to the different asymmetrical charge densities. The mechanical properties and their anisotropies are calculated for different lattice directions and visualized through 2D and 3D graphs. Based on the actual bonding characteristics, the bond resistance model with Phillips ionicity and Mulliken bond overlap populations, the bond electronegativity model, and the bond valence model, the hardnesses of the stable structures are calculated by each model. It is found that the stable structures have hardnesses spanning a wide range of 8–35 GPa due to the different models. The origin and dynamic instability of the unstable structures are examined. It is concluded that the existence of Li atoms and different chains, which include the different electronegativity of atoms within the structure, have essential roles in charge transfers, chain geometries, vibrational behavior, and then the stability of the structures.

Shadow Molecular Dynamics and Atomic Cluster Expansions for Flexible Charge Models.

A shadow molecular dynamics scheme for flexible charge models is presented where the shadow Born-Oppenheimer potential is derived from a coarse-grained approximation of range-separated density functional theory. The interatomic potential, including the atomic electronegativities and the charge-independent short-range part of the potential and force terms, is modeled by the linear atomic cluster expansion (ACE), which provides a computationally efficient alternative to many machine learning methods. The shadow molecular dynamics scheme is based on extended Lagrangian (XL) Born-Oppenheimer molecular dynamics (BOMD) [Eur. Phys. J. B 2021, 94, 164]. XL-BOMD provides stable dynamics while avoiding the costly computational overhead associated with solving an all-to-all system of equations, which normally is required to determine the relaxed electronic ground state prior to each force evaluation. To demonstrate the proposed shadow molecular dynamics scheme for flexible charge models using atomic cluster expansion, we emulate the dynamics generated from self-consistent charge density functional tight-binding (SCC-DFTB) theory using a second-order charge equilibration (QEq) model. The charge-independent potentials and electronegativities of the QEq model are trained for a supercell of uranium oxide (UO2) and a molecular system of liquid water. The combined ACE+XL-QEq molecular dynamics simulations are stable over a wide range of temperatures both for the oxide and for the molecular systems and provide a precise sampling of the Born-Oppenheimer potential energy surfaces. Accurate ground Coulomb energies are produced by the ACE-based electronegativity model during an NVE simulation of UO2, predicted to be within 1 meV of those from SCC-DFTB on average during comparable simulations.

Quantum Alchemy Based Bonding Trends and Their Link to Hammett's Equation and Pauling's Electronegativity Model.

We present an intuitive and general analytical approximation estimating the energy of covalent single and double bonds between participating atoms in terms of their respective nuclear charges with just three parameters, [EAB ≈ a - bZAZB + c(ZA7/3 + ZB7/3) ]. The functional form of our expression models an alchemical atomic energy decomposition between participating atoms A and B. After calibration, reasonably accurate bond dissociation energy estimates are obtained for hydrogen-saturated diatomics composed of p-block elements coming from the same row 2 ≤ n ≤ 4 in the periodic table. Corresponding changes in bond dissociation energies due to substitution of atom B by C can be obtained via simple formulas. While being of different functional form and origin, our model is as simple and accurate as Pauling's well-known electronegativity model. Analysis indicates that the model's response in covalent bonding to variation in nuclear charge is near-linear, which is consistent with Hammett's equation.

QSAR Studies, Molecular Docking, Molecular Dynamics, Synthesis, and Biological Evaluation of Novel Quinolinone-Based Thiosemicarbazones against Mycobacterium tuberculosis.

In this study, a series of novel quinolinone-based thiosemicarbazones were designed in silico and their activities tested in vitro against Mycobacterium tuberculosis (M. tuberculosis). Quantitative structure-activity relationship (QSAR) studies were performed using quinolinone and thiosemicarbazide as pharmacophoric nuclei; the best model showed statistical parameters of R2 = 0.83; F = 47.96; s = 0.31, and was validated by several different methods. The van der Waals volume, electron density, and electronegativity model results suggested a pivotal role in antituberculosis (anti-TB) activity. Subsequently, from this model a new series of quinolinone-thiosemicarbazone 11a-e was designed and docked against two tuberculosis protein targets: enoyl-acyl carrier protein reductase (InhA) and decaprenylphosphoryl-β-D-ribose-2'-oxidase (DprE1). Molecular dynamics simulation over 200 ns showed a binding energy of -71.3 to -12.7 Kcal/mol, suggesting likely inhibition. In vitro antimycobacterial activity of quinolinone-thiosemicarbazone for 11a-e was evaluated against M. bovis, M. tuberculosis H37Rv, and six different strains of drug-resistant M. tuberculosis. All compounds exhibited good to excellent activity against all the families of M. tuberculosis. Several of the here synthesized compounds were more effective than the standard drugs (isoniazid, oxafloxacin), 11d and 11e being the most active products. The results suggest that these compounds may contribute as lead compounds in the research of new potential antimycobacterial agents.

Supplementary data: Quantum Alchemy Based Bonding Trends and Their Link to Hammett's Equation and Pauling's Electronegativity Model

Supplementary data: Quantum Alchemy Based Bonding Trends and Their Link to Hammett's Equation and Pauling's Electronegativity Model

Cover Feature: The Chemical Bond: When Atom Size Instead of Electronegativity Difference Determines Trend in Bond Strength (Chem. Eur. J. 63/2021)

Atom size, not electronegativity difference, determines C−X bond strength, which weakens from X=F to I. In their Communication (DOI: 10.1002/chem.202103544), M. Bickelhaupt et al. reveal that, as the atom size increases, it is the increase in steric Pauli repulsion that weakens the C−X bond, and not the weakening of the orbital interaction (which, in fact, strengthens it!), as is traditionally considered in the electronegativity model. With state-of-the-art DFT calculations, they provide compelling evidence to challenge the electronegativity model.

A Scale of Atomic Electronegativity Based on Floating Spherical Gaussian Orbital Approach

AbstractElectronegativity (χ) is an old yet valuable concept having multidisciplinary applications. To advance the understanding of this concept, an electronegativity model has been proposed based on polarizability within the context of Floating Spherical Gaussian Orbital (FSGO) approach. The model provides atomic electronegativity scale for 120 elements. The calculated electronegativity presents marked periodicity and relates well with other electronegativity scales. Further, Electronegativity Equalization Principle is validated by the computed electronegativity data. The proposed scale has also been successfully applied to compute Fermi energy for some metal oxides. In accordance with the literature, this is the first FSGO‐polarizability based model of electronegativity.

Intrinsic hardness of covalent crystals: a unified multiparametric framework

Bond resistance, bond strength and electronegativity models have been widely utilized for predicting intrinsic hardness of novel covalent materials. Although these models are generally perceived to be distinct, this manuscript recognizes them to be drawing input parameters from the same basis set comprising of bond density, bond length, electronegativity, and coordination number, while primarily differing in the exponents assigned to them. A numerical bound on the feasible space of these exponents is derived, followed by a search operation of this space to determine optimal values. The resulting model yields hardness estimates in good conformance with experimental data for numerous binary and ternary ceramic compounds. The study also provides a plausible explanation for the diversity of parameter–exponent combinations in the existing intrinsic hardness models, that is derived from the variability exhibited by these exponents in capturing a given experimental dataset at a constant fitting error.

A new approach for modelling the damped Helmholtz oscillator: applications to plasma physics and electronic circuits

In this paper, a new approach is devoted to find novel analytical and approximate solutions to the damped quadratic nonlinear Helmholtz equation (HE) in terms of the Weiersrtrass elliptic function. The exact solution for undamped HE (integrable case) and approximate/semi-analytical solution to the damped HE (non-integrable case) are given for any arbitrary initial conditions. As a special case, the necessary and sufficient condition for the integrability of the damped HE using an elementary approach is reported. In general, a new ansatz is suggested to find a semi-analytical solution to the non-integrable case in the form of Weierstrass elliptic function. In addition, the relation between the Weierstrass and Jacobian elliptic functions solutions to the integrable case will be derived in details. Also, we will make a comparison between the semi-analytical solution and the approximate numerical solutions via using Runge–Kutta fourth-order method, finite difference method, and homotopy perturbation method for the first-two approximations. Furthermore, the maximum distance errors between the approximate/semi-analytical solution and the approximate numerical solutions will be estimated. As real applications, the obtained solutions will be devoted to describe the characteristics behavior of the oscillations in RLC series circuits and in various plasma models such as electronegative complex plasma model.

Model prediction of the point of zero net charge of layered double hydroxides and clay minerals

Many models such as electrostatic, crystallographic, and electronegativity models have been developed to predict the point of zero net charge (PZNC) of (hydr)oxides without structural charge. Nevertheless, there is still a lack of feasible models to predict the PZNC of structurally charged amphoteric solids, such as positively charged layered double hydroxides (LDHs) and negatively charged clay minerals, using easily available characteristic physical constants. Herein, a new model, called general “electrostatic–electronegativity” (ESEN) model, was proposed based on the classical electrostatic and electronegativity models by taking into account the structural charge (σst). The new model correlates the PZNC of amphoteric solids with σst and easily available characteristic physical constants (ionic valence, ionic radius, and electronegativity). The empirical parameters in the model were simulated using the PZNC data of 22 (hydr)oxides previously reported. The so-obtained ESEN model equations can predict the PZNC of (hydr)oxides, LDHs, and silicate clay minerals with acceptable feasibility and accuracy. To the best of our knowledge, this is the first feasible model to predict the PZNC of both LDHs and silicate clay minerals using easily available characteristic physical constants, which is important for the design synthesis and application of new materials.

Intrinsic hardness of boron carbide: Influence of polymorphism and stoichiometry

AbstractBoron carbide comprises of polymorphs that differ in crystallographic arrangement and stoichiometry. Consequently, specimens extracted from the same batch can exhibit variability in mechanical properties depending on the constituent mixture of polymorphs. In this work, density functional theory simulations and estimates from three models (bond resistance model, bond strength model, and electronegativity model) are utilized to (i) investigate the influence of polymorphism and stoichiometry on the intrinsic hardness of boron carbide, (ii) reveal the sensitivity of the estimates to the model used, and (iii) test their conformance to experimental data. The study finds intrinsic hardness of boron carbide to be primarily a function of stoichiometry, with polymorphism having a lower influence. Furthermore, hardness estimates are shown to exhibit substantial sensitivity to the model used, differing by as much as 9 GPa for the same polymorph. Thus, the search for new superhard materials should be guided by more than just one model. Our analysis finds bond resistance model to offer the best conformance to experimental data, indicating that bond length is a much stronger influencer of intrinsic hardness in covalent crystals than coordination numbers and electronegativities of bonding atoms.

Floating potential calculation for a Langmuir probe in electronegative plasmas and experimental validation in a glow discharge

A radial Langmuir probe sheath model is used to make a prediction of the floating potential of a Langmuir probe immersed in an electronegative plasma. The new electronegative plasma sheath model takes into account the positive ion and the negative ion thermal energies and is valid for any ion temperature value. The values predicted can be used for diagnosing and controlling an electronegative plasma, and we compare them with measurements of the floating potential in an Argon plasma and in a Neon plasma with with two distinct electron populations at different temperatures. We have found that the agreement is very good in a wide range of plasma pressure and discharge current values, and thus the model is applicable for electronegative plasmas. Moreover, the model can be used to measure the energy with which the ions will collide with the surface of the probe.

Role of electronegativity on the bulk modulus, magnetic moment and band gap of Co2MnAl based Heusler alloys

Abstract In this paper, we have presented the comparative study of mechanical, electrical and magnetic properties of Co2MnAl1−xZx Heusler alloy with Z = Si, Ge and Ga and x = 0, 0.25, 0.75 and 1 using electronegativity (EN) model. We employed density functional theory for numerical calculations. It is found that Co2MnAl1−xZx with Z = Ga, Ge follow the Vegard's law while Co2MnAl1−xSix does not follow the same trend. Among all composition Co2MnAl.25Si.75 alloy is found to be more compressible. Electronic density distribution depicts the ionic nature of Co2MnAl1−xZx alloy systems. The Co2MnAl1−xZx with Z = Si, Ge possess larger magnetic moment and band gap with respect to Co2MnAl1−xGax system which results from the EN difference, degree of delocalization of valence electron, atomic size and atomic number, respectively.

FTIR and dispersive gas phase fundamental infrared intensities of the fluorochloromethanes: Comparison with QCISD/cc-pVTZ results

New experimental values of the fundamental infrared gas phase intensities of the fluorochloromethanes have been determined by integrating the areas of vibrational bands contained in the PNNL spectral library using homemade software. The root mean square differences of these values and averages of experimental values determined at lower resolution during the latter part of the 20th century is 26.6 km mol−1. All but one of the low resolution intensities are smaller than the PNNL values. The exception is the ν1,ν4 overlapped band intensity of CF3Cl that has a standard deviation of the low resolution values of ±112.5 km mol−1, larger than the observed difference of 102.5 km mol−1. The use of an augmented triple zeta basis set at the QCISD level results in an rms difference of only 8.4 km mol−1 for the fluoro- and chloromethane PNNL intensities, whereas a comparison of these with results at the QCISD/cc-pVTZ level produces an error twice as large, 16.2 km mol−1. As such these results suggest that future comparisons of theoretical intensities with experimental values should take into account integrated intensities that can be obtained from hundreds of spectra in the PNNL library. Furthermore, the intensity values obtained from the PNNL spectra confirm electronegativity model results previously reported based on the low resolution intensities.

Electronegative (3+1)-dimensional modulated excitations in plasmas

A three-dimensional electronegative plasma model is studied. Modulated ion-acoustic waves are investigated via the activation of modulational instability in the Davey-Stewartson equations, with three space variables. The contributions of the modulation angle (θ) and electronegative plasma parameters are discussed to that effect, including some particular cases such as the parallel and transverse modulations. The parametric linear stability analysis that is proposed shows that the growth rate of instability displays opposite regions of instability for parallel and transverse modulations when the negative ion concentration ratio (α) and the electron-to-negative ion temperature ratio (σn) change.

Electronic Support Effects of Tunable Mixed Metal Oxides on Immobilized Palladium N‐Heterocyclic Carbene Complexes

Electronic effects of supports on site‐isolated organometallic complexes are poorly understood, despite indication that such effects impact stability and reactivity of immobilized complexes. Here we report X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption near edge structure (XANES) spectroscopy studies of surface‐immobilized PdII N‐heterocyclic carbene complexes on Mg‐Al mixed metal oxides (MMOs) using silane‐modified ligands. XPS revealed a ca. 1 eV increase in Pd binding energy as a result of immobilization on MMOs, suggesting that the PdII complex becomes more electropositive when appended to the surface. For MMOs doped with Fe, Ni, Co and Zn, analysis of Cl K‐edge and Pd L2‐ and L3‐edge showed increasing pre‐edge energies that followed the order Fe = Ni < Zn = Cr < undoped Mg‐Al MMO. The Pd L3 pre‐edge energies correlated to the calculated oxygen partial charge of the MMO, as estimated using the Sanderson electronegativity model. Transmission electron microscope images collected on the immobilized Pd complexes revealed nanoparticles on three of the five MMOs, whose presence can be related to the Pd XPS and XANES energies. These findings suggest that electronic differences associated with the MMO supports impact the stability of appended PdII complexes with respect to reduction to Pd0.

Evaluation of oxygen species during E–H transition in inductively coupled RF plasmas: combination of experimental results with global model

Inductively coupled RF plasmas (ICP) in oxygen at low pressure have been intensively studied as a molecular and electronegative model system in the last funding period of the Collaborative Research Centre 24 “Fundamentals of Complex Plasmas”. The ICP configuration consists of a planar coil inside a quartz cylinder as dielectric barrier which is immersed in a large stainless steel vacuum chamber. In particular, the E–H mode transition has been investigated, combining experimental results from comprehensive plasma diagnostics as input for analytical rate equation calculation of a volume averaged global model. The averaged density was determined for electrons, negative ions O−, molecular oxygen ground state O2(X3 Σg−) and singlet metastable state O2(a1 ∆g) from line-integrated measurements using 160 GHz Gaussian beam microwave interferometry coupled with laser photodetachment experiment and VUV absorption spectroscopy, respectively. Taking into account the relevant elementary processes and rate coefficients from literature together with the measured temperatures and averaged density of electrons, O2(X3 Σg−) and O2(a1 ∆g) the steady state density was calculated for O(3P), O2(b1 Σg+), O(1D), O(1S), O3, O−, O2−, and O3−, respectively. The averaged density of negative ions O− from the rate equation calculation is compared with the measured one. The normalized source and loss rates are discussed for O(3P), O2(b1 Σg+) and O−.

Layered double hydroxide modified by PEGylated hyaluronic acid as a hybrid nanocarrier for targeted drug delivery

In recent years, organic-inorganic hybrid nanocarriers are explored for effective drug delivery and preferable disease treatments. In this study, using 5-fluorouracil(5-FU)as electronegative model drug, a new type of organic-inorganic hybrid drug delivery system(LDH/HA-PEG/5-FU)was conceived and manufactured by the adsorption of PEGylated hyaluronic acid(HA-PEG)on the surface of layered double hydroxide(LDH, prepared via hydrothermal method)and the intercalation of 5-FU in the interlamination of LDH via ion exchange strategy. The drug loading amount of LDH/HA-PEG/5-FU achieved as high as 34.2%. LDH, LDH/5-FU and LDH/HA-PEG/5- FU were characterized by FT-IR, XRD, TGA, laser particle size analyzer and SEM. With the benefit of pHdegradable feature of LDH and enzyme-degradable feature of HA, LDH/HA-PEG/5-FU showed pH-degradable and enzyme-degradable capacity in in vitro drug release. Moreover, the drug carrier LDH/HA-PEG contained biocompatible PEG and tumor-targeted HA, resulting in lower cytotoxicity and better endocytosis compared with LDH in vitro. It was suggested that the organic-inorganic hybrid drug delivery system, which was endowed with the properties of controlled release, low toxicity and tumor-targeting delivery for ameliorative cancer therapy, was advisable and might be applied further to fulfill other treatments.