Charge Density Studies Research Articles

Advanced computational study of different boron nitride-based nanospheres for removal of organic contaminants from wastewater system

In the present work the removal of organic pollutants from wastewater was studied using a computational simulation method. Two nanospherical porous boron nitride (BN) materials namely, B16N16 and B12N12, were selected as adsorbent and the removal mechanism and adsorption ability of pure and glycine functionalized boron nitride adsorbents (B16N16(Glycine)2/B12N12(Glycine)2) were comprehensively evaluated in removal of two different emerging contaminants. The sigma profile (or charge density) study along with the quantum chemical calculations (using Materials Studio software) were obtained and discussed to predict the contaminant removal process.In particular, the adsorption ability and possible changes in the spectroscopic and electronic properties (Frontier molecular orbital, energy gap (ΔEGAP), chemical softness (σ), hardness (η)) of the pure and functionalized BN adsorbents before and after adsorption processes were studied. It was found that both functionalized adsorbents (B16N16(Glycine)2 and B12N12(Glycine)2) had higher adsorption ability. Moreover, according to the quantum chemical calculations B16N16(Glycine)2 adsorbent showed higher chemical reactivity and adsorption ability compare to other studied adsorbents due to the formation of cage interactions between pollutants and amino acid glycine of BN. According to the outcomes, Functionalization of the nanospherical boron nitride materials with glycine led to improvement in the pollutants adsorption affinity.

Factors Influencing Piezoelectric Response of Horizontally and Vertically Embedded PZT Patch in Confined Granular Fills

The energy harvesting from ambient vibrations in the confined granular fill along the expressways and highways is a prospective power source for varied engineering applications. This paper presents the study of charge density, voltage output, and power from the PZT (lead zirconate titanate) patches embedded in dynamically loaded confined granular fill. The effect of the alignment of PZT patches, thickness ratio, material properties of the confined granular fill, and retaining structure on the voltage output is investigated. It provides the scope for the evaluation of voltage output directly from the stress-strain response, position of the PZT patch, and the engineering properties of the confined granular fill. The alignment of PZT patches in the horizontal and vertical directions has been examined analytically to optimize voltage outputs. The results indicate that the modulus ratio of the material, alignment of PZT patches, and gradation of infill material significantly affect the voltage generation. A relationship for voltage and power output has been proposed for a set of engineering applications. The observed voltage output is found appropriate for wide-ranging implements classified as low- (LRA), medium- (MRA), and high- (HRA) resistance applications. It is proposed to be up-scaled using multiple patches embedded throughout the confined granular fill and pavements subjected to continuous dynamic loads.

The Relevance of Experimental Charge Density Analysis in Unraveling Noncovalent Interactions in Molecular Crystals.

The work carried out by our research group over the last couple of decades in the context of quantitative crystal engineering involves the analysis of intermolecular interactions such as carbon (tetrel) bonding, pnicogen bonding, chalcogen bonding, and halogen bonding using experimental charge density methodology is reviewed. The focus is to extract electron density distribution in the intermolecular space and to obtain guidelines to evaluate the strength and directionality of such interactions towards the design of molecular crystals with desired properties. Following the early studies on halogen bonding interactions, several “sigma-hole” interaction types with similar electrostatic origins have been explored in recent times for their strength, origin, and structural consequences. These include interactions such as carbon (tetrel) bonding, pnicogen bonding, chalcogen bonding, and halogen bonding. Experimental X-ray charge density analysis has proved to be a powerful tool in unraveling the strength and electronic origin of such interactions, providing insights beyond the theoretical estimates from gas-phase molecular dimer calculations. In this mini-review, we outline some selected contributions from the X-ray charge density studies to the field of non-covalent interactions (NCIs) involving elements of the groups 14–17 of the periodic table. Quantitative insights into the nature of these interactions obtained from the experimental electron density distribution and subsequent topological analysis by the quantum theory of atoms in molecules (QTAIM) have been discussed. A few notable examples of weak interactions have been presented in terms of their experimental charge density features. These examples reveal not only the strength and beauty of X-ray charge density multipole modeling as an advanced structural chemistry tool but also its utility in providing experimental benchmarks for the theoretical studies of weak interactions in crystals.

Si-H···Se Chalcogen-Hydride Bond Quantified by Diffraction and Topological Analyses.

The Si-H···Se contact in 1-mesitylselanyl-8-(dimethylsilyl)naphthalene (1), which exhibits the spatial arrangement of a δ-agostic interaction from geometric considerations, was investigated. Is this just enforced by close 1,8-proximity or is this a favorable interaction? Charge density studies are best suited to investigate the exact origin of the interaction and to quantify the properties. Hence, they are most elucidating. High-resolution X-ray diffraction data of 1 were collected, and a multipole refinement followed by a topological analysis using Bader's quantum theory of atoms in molecules was employed. The resulting bond properties were set in relation to high-level computational parameters. The comparison to Si-H···[M] agostics, hydride bonding, chalcogen bonds, and charge-inverted hydrogen bonds qualified the Si-H···Se noncovalent interaction to be best classified as a chalcogen-hydride bond.

Charged lithium adsorption on pristine and defective silicene: a theoretical study

We investigated by first principle calculations the adsorption of Li q (q = −1, 0 or +1) on a silicene single layer. Pristine and three different defective silicene configurations with and without Li doping were studied: single vacancy (SV), double vacancy (DV) and Stone–Wales (STW). Structural studies and the adsorption energies of various sites were obtained and compared in order to understand the stability of the Li on the surface. Moreover, electronic structure and charge density difference analysis were performed before and after adsorption at the most stables sites, which showed the presence of a magnetic moment in the undoped SV system, the displacement of the Fermi level produced by Li doping and a charge transfer from Li to the surface. Additionally, quantum capacity (QC) and charge density studies were performed on these systems. This analysis showed that the generation of defects and doping improves the QC of silicene in positive bias, because of the existence of 3p orbital in the zone of the defect. Consequently, the innovative calculations performed in this work of charged lithium doping on silicene can be used for future comparison with experimental studies of this Li-ion battery anode material candidate.

Computational Study of Charge Density Produced in N2:H2 Plasma Actuator

Numerical simulation of charge density produced in plasma actuators is dependent upon the development of models dealing with electrical properties. The main aim of this work is to investigate the characteristics surface charge density and space charge density of DBD plasma actuator. A simple design of surface dielectric barrier discharge plasma actuator is used in the study. The discharge gas was N2:H2 mixture with applied voltage equal to 1.5 kV. A theoretical plasma model is used to establish the charge density details. Results show that surface charge density increased in value and spread in width alone the exposed electrode as the voltage increased and reached to the amplitude value.
 HIGHLIGHTS
 
 In plasma diagnostics studies, charge density is one of the important parameter
 The paper includes simulation to charge density in plasma actuator with two gases which are N2 and H2
 The results very useful to follow up the electric field and flow of gases

Computational Study of Charge Density Produced in N2:H2 Plasma Actuator

Numerical simulation of charge density produced in plasma actuators is dependent upon the development of models dealing with electrical properties. The main aim of this work is to investigate the characteristics surface charge density and space charge density of DBD plasma actuator. A simple design of surface dielectric barrier discharge plasma actuator is used in the study. The discharge gas was N2:H2 mixture with applied voltage equal to 1.5 kV. A theoretical plasma model is used to establish the charge density details. Results show that surface charge density increased in value and spread in width alone the exposed electrode as the voltage increased and reached to the amplitude value.
 HIGHLIGHTS
 
 In plasma diagnostics studies, charge density is one of the important parameter
 The paper includes simulation to charge density in plasma actuator with two gases which are N2 and H2
 The results very useful to follow up the electric field and flow of gases
 
 GRAPHICAL ABSTRACT

Accurate experimental characterization of the labile N–Cl bond inN-chloro-N′-(p-fluorophenyl)-benzamidine crystal at 17.5 K

Very low temperature can preserve the photolabile N–Cl bond in aN-chloro-N-benzamidine derivative long enough to carry on an accurate experimental X-ray charge density study.

Charge density studies of single and transient (single to double) boron-oxygen bonds in (NH4)2B4O5(OH)4·2H2O.

A H4B4O92- ion which makes up the (NH4)2B4O5(OH)4·2H2O crystal structure has two types of boron-oxygen bonds, i.e. single B-O bonds and an intermediate between single and double BO bonds. Differences between these two bond types are visible not only because they differ by their lengths but also a topology of electron density distribution differs. This also gives a hint as to how to distinguish between these two bond types. Experimental results based on multipole model refinement gave excellent agreement with theoretical calculations and literature data. Calculations at bond critical points for B-O and BO (electron density, the Laplacian of electron density and the localized-orbital locator function) suggest us how boron-oxygen bonds should be categorised with respect to compounds previously reported in the literature. Additionally, a novel synthesis method for the investigated compound has been developed, which involves crystallization from an aqueous solution of BH3NH3 dissolved in a mixture of tetrahydrofuran and water.

An experimental and theoretical charge density study of theophylline and malonic acid cocrystallization.

The pharmaceutical agent theophylline (THEO) is primarily used as a bronchodilator and is commercially available in both tablet and liquid dosage forms. THEO is highly hygroscopic, reducing its stability, overall shelf-life, and therefore usage as a drug. THEO and dicarboxylic acid cocrystals were designed by Trask et al. in an attempt to decrease the hygroscopic behaviour of THEO; cocrystallisation of THEO with malonic acid (MA) did not improve the hygroscopic stability of THEO in simulated atmospheric humidity testing. The current study employed high-resolution X-ray crystallography, and Density Functional Theory (DFT) calculations to examine the electron density distribution (EDD) changes between the cocrystal and its individual components. The EED changes identified the reasons why the THEO:MA cocrystal did not alter the hygroscopic profile of THEO. The cocrystal was equally porous, with atomic packing factors (APF) similar to those of THEO 0.73 vs. 0.71, respectively. The THEO:MA (1) cocrystal structure is held together by an array of interactions; a heterogeneous synthon between the imidazole and a carboxylic fragment stabilising the asymmetric unit, a pyrimidine-imidazole homosynthon, and an aromatic cycle stack between two THEO moieties have been identified, providing 9.7–12.9 kJ mol−1 of stability. These factors did not change the overall relative stability of the cocrystal relative to its individual THEO and MA components, as shown by cocrystal (1) and THEO being equally stable, with calculated lattice energies within 2.5 kJ mol−1 of one other. The hydrogen bond analysis and fragmented atomic charge analysis highlighted that the formation of (1) combined both the EDD of THEO and MA with no net chemical change, suggesting that the reverse reaction — (1) back to THEO and MA — is of equal potential, ultimately producing THEO hydrate formation, in agreement with the work of Trask et al. These results highlight that a review of the EDD change associated with a chemical reaction can aid in understanding cocrystal design. In addition, they indicate that cocrystal design requires further investigation before becoming a reliable process, with particular emphasis on identifying the appropriate balance of synthon engineering, weak interactions, and packing dynamics.

X-ray wavefunction refinement and comprehensive structural studies on bromo-substituted analogues of 2-deoxy-d-glucose in solid state and solution.

The structural studies on two bromo-substituted derivatives of 2-deoxy-d-glucose (2-DG), namely 2-deoxy-2-bromo-d-glucose (2-BG) and 2-deoxy-2-bromo-d-mannose (2-BM) are described. 2-DG itself is an inhibitor of hexokinase, the first enzyme in the glycolysis process, playing a vital role in both cancer cell metabolism and viral replication in host cells. Because of that, 2-DG derivatives are considered as potential anti-cancer and anti-viral drugs. An X-ray quantum crystallography approach allowed us to obtain more accurate positions of hydrogen atoms by applying Hirshfeld atom refinement, providing a better description of hydrogen bonding even in the case of data from routine X-ray experiments. Obtained structures showed that the introduction of bromine at the C2 position in the pyranose ring has a minor influence on its conformation but still, it has a noticeable effect on the crystal structure. Bromine imposes the formation of a layered supramolecular landscape containing hydrogen bonds, which involves the bromine atom. Periodic DFT calculations of cohesive and interaction energies (at the B3LYP level of theory) have supported these findings and highlighted energetic changes upon bromine substitution. Based on molecular wavefunction from the refinement, we calculated the electrostatic potential, Laplacian, and ELI-D, and applied them to charge-density studies, which confirmed the geometry of hydrogen bonding and involvement of the bromine atom with these intermolecular interactions. NMR studies in the solution show that both compounds do not display significant differences in their anomeric equilibria compared to 2-DG, and the pyranose ring puckering is similar in both aqueous and solid state.

Structural and switching ferroelectric charge density studies in BaTi0.95Sn0.05O3 prepared by microwave assisted sintering

Lead free ferroelectric perovskite compounds (ABO3) have received so much attention due to the toxic nature of lead. Among them, barium titanate is the promising lead free ferroelectric material. But this material needs more investigation to explore its technological application. To analysize the various properties such as structural and ferroelectric of polycrystalline BaTi0.95Sn0.05O3 (BTSO), it was synthesized by the Solid State method. The X-ray diffraction patterns confirmed the crystallinity of the sample. The Rietveld refinement shows that the prepared sample crystallizes to tetragonal symmetry with P4mm space group. The surface morphology of the sample was studied by using the Field Emission Scanning Electron Microscopy (FE-SEM) and the grain size of the sample was estimated with the help of Image J software. The enhancement of maximum polarization (Pmax), remnant polarization (Pr), and coercive field (Ec) with the applied electric field confirm the ferroelectric nature of the prepared sample. The Positive Up Negative Down (PUND) measurement confirms the enhanced behavior of the true switching ferroelectric charge density(QSW) concerning the applied electric field.

Understanding Hygroscopicity of Theophylline via a Novel Cocrystal Polymorph: A Charge Density Study.

The charge density distribution in a novel cocrystal (1) complex of 1,3-dimethylxanthine (theophylline) and propanedioic acid (malonic acid) has been determined. The molecules crystallize in the triclinic, centrosymmetric space group P1̅, with four independent molecules (Z = 4) in the asymmetric unit (two molecules each of theophylline and malonic acid). Theophylline has a notably high hygroscopic nature, and numerous cocrystals have shown a significant improvement in stability to humidity. A charge density study of the novel polymorph has identified interesting theoretical results correlating the stability enhancement of theophylline via cocrystallization. Topological analysis of the electron density highlighted key differences (up to 17.8) in Laplacian (∇2ρ) between the experimental (EXP) and single-point (SP) models, mainly around intermolecular-bonded carbonyls. Further investigation via molecular electrostatic potential maps reaffirmed that the charge redistribution enhanced intramolecular hydrogen bonding, predominantly for N(2') and N(2) (61.2 and 61.8 kJ mol-1, respectively). An overall weaker lattice energy of the triclinic form (-126.1 kJ mol-1) compared to that of the monoclinic form (-133.8 kJ mol-1) suggests a lower energy threshold to overcome to initiate dissociation. Future work via physical testing of the novel cocrystal in both dissolution and solubility will further solidify the correlation between theoretical and experimental results.

Mapping of N-C Bond Formation from a Series of Crystalline Peri-Substituted Naphthalenes by Charge Density and Solid-State NMR Methodologies.

A combination of charge density studies and solid state nuclear magnetic resonance (NMR) 1 J NC coupling measurements supported by periodic density functional theory (DFT) calculations is used to characterise the transition from an n–π* interaction to bond formation between a nucleophilic nitrogen atom and an electrophilic sp 2 carbon atom in a series of crystalline peri‐substituted naphthalenes. As the N⋅⋅⋅C distance reduces there is a sharp decrease in the Laplacian derived from increasing charge density between the two groups at ca. N⋅⋅⋅C = 1.8 Å, with the periodic DFT calculations predicting, and heteronuclear spin‐echo NMR measurements confirming, the 1 J NC couplings of ≈3–6 Hz for long C−N bonds (1.60–1.65 Å), and 1 J NC couplings of <1 Hz for N⋅⋅⋅C >2.1 Å.

Mapping of N−C Bond Formation from a Series of Crystalline Peri‐Substituted Naphthalenes by Charge Density and Solid‐State NMR Methodologies

AbstractA combination of charge density studies and solid state nuclear magnetic resonance (NMR) 1JNC coupling measurements supported by periodic density functional theory (DFT) calculations is used to characterise the transition from an n–π* interaction to bond formation between a nucleophilic nitrogen atom and an electrophilic sp2 carbon atom in a series of crystalline peri‐substituted naphthalenes. As the N⋅⋅⋅C distance reduces there is a sharp decrease in the Laplacian derived from increasing charge density between the two groups at ca. N⋅⋅⋅C = 1.8 Å, with the periodic DFT calculations predicting, and heteronuclear spin‐echo NMR measurements confirming, the 1JNC couplings of ≈3–6 Hz for long C−N bonds (1.60–1.65 Å), and 1JNC couplings of &lt;1 Hz for N⋅⋅⋅C &gt;2.1 Å.

Experimental and theoretical charge-density study of two tetranuclear transition metal clusters with single-molecule magnet properties

Experimental and theoretical charge-density study of two tetranuclear transition metal clusters with single-molecule magnet properties

Use of transferrable multipoles to extend the range of X-ray charge-density study to variable temperature and high pressure

Use of transferrable multipoles to extend the range of X-ray charge-density study to variable temperature and high pressure

Charge-density studies of in situ crystallized liquids with Hirshfeld atom refinement, invariom model and multipole model

Charge-density studies of <i>in situ</i> crystallized liquids with Hirshfeld atom refinement, invariom model and multipole model

Exploration of (1−x)BaTiO3 + xZnFe2O4 magneto-electric ceramic composite on charge density: Structure and its characterization

Magneto-electric ceramic composite of (1−x)BaTiO3 + xZnFe2O4 (x = 0.2, 0.4, 0.6, 0.8) was prepared by solid state synthesis method. Powder XRD confirms the presence of two distinct phases (BaTiO3 and ZnFe2O4) as tetragonal and cubic. Charge density distribution in the unit cells of BaTiO3 and ZnFe2O4 were analyzed and correlated with the observed results of the characterization. The PE characterization of the electrical studies reveals that the prepared composite changes from lossy capacitance and to resistive capacitance with the increase in the ferrite composition. For x = 0.8 (20% BaTiO3; 80% ZnFe2O4), the dielectric constant is the maximum. The dielectric loss increases with the increase in the ferrite content. From the charge density studies, it can be inferred that the TiO bond assumes a major role in elucidating the electrical characterization of the prepared composite. The magnetic characterization confirms the presence of small ferromagnetic property in the composite. Saturation magnetization varies from 0.583 emu/g to 1.359 emu/g at room temperature with an increase in the ferrite content. In addition to the ferrite content in the composite, the charge density between the atoms is also responsible for the magnetization of the composite.

Experimental charge-density analysis towards predictive materials science

The ongoing increase in the number of experimental charge-density studies can be related to both the technological advancements and the wide applicability of the method. Regarding materials science, the understanding of bonding features and their relation to the physical properties of materials can not only provide means to optimize such properties, but also to predict and design new materials with the desired ones. In this tutorial, we describe the steps for a charge-density analysis, emphasizing the most relevant features and briefly discussing the applications of the method.