Electron Density Difference Research Articles

Systematic surface bowing in 2D III-nitride monolayers.

In this article we report novel composite materials of bucky ball (C60 fullerene) and III-nitrides (BN, AlN, GaN, InN). The experimental feasibility of the novel composite materials is confirmed through negative binding energies and molecular dynamics simulations performed at 500 K. The structural properties of the novel composites are explored through density functional theory. An unusual phenomenon of surface bowing is observed in the 2D structure of the III-nitride monolayers due to the C60 sticking. This surface bowing systematically increases as one proceeds from BN → AlN → GaN → InN. The electron density difference and Hirshfeld charge density analysis show smaller charge transfer during the complexation, which is probably due to weak van der Waal's forces. The presence of van der Waal's forces is also confirmed by the Atom in Molecule analysis, Reduced Density Gradient Technique and Non-covalent Interaction analysis. This work provides a foundation for further theoretical and experimental studies of the novel phenomenon of systematic bowing in the 2D structure of III-nitride monolayers.

Intramolecular charge transfer enhanced optical limiting in novel hydrazone derivatives with a D1-D-Ai-π-A structure.

The present paper investigates one of the hydrazone derivatives (BTH with a D-π-A structure) based on density functional theory. With the computation results of ground state absorption (GSA), excited-state absorption (ESA) and multi-photon absorption (MPA), the optical limiting effect observed in the experiment for the BTH molecule can be well predicted and elucidated by the MPA-ESA mechanism. The analysis of the hole-electron and the electron density differences between two transition states reveal that the main transitions involved in the GSA and ESA of BTH could be recognized as local excitation. Based on these observations, four novel hydrazone derivatives based on the BTH unit with a D1-D-Ai-π-A structure were designed to promote intramolecular charge transfer (ICT). It shows that the ICT effect is well improved by adding the D1 and Ai units. Compared with the original BTH molecule, the main bands of GSA and ESA of D1-D-Ai-π-A molecules are both red-shifted. In addition, GSA, ESA and MPA probabilities are all improved because the obvious charge transfer character results in the transition dipole moment change from localized to delocalized. Accordingly, the optical limiting effect in these hydrazone derivatives is well enhanced. These observations provide guidance for designing novel optical limiting materials based on the hydrazone derivatives.

Exploring the stability and aromaticity of rare earth doped tin cluster MSn16- (M = Sc, Y, La).

Rare earth elements have high chemical reactivity, and doping them into semiconductor clusters can induce novel physicochemical properties. The study of the physicochemical mechanisms of interactions between rare earth and tin atoms will enhance our understanding of rare earth functional materials from a microscopic perspective. Hence, the structure, electronic characteristics, stability, and aromaticity of endohedral cages MSn16- (M = Sc, Y, La) have been investigated using a combination of the hybrid PBE0 functional, stochastic kicking, and artificial bee colony global search technology. By comparing the simulated results with experimental photoelectron spectra, it is determined that the most stable structure of these clusters is the Frank-Kasper polyhedron. The doping of atoms has a minimal influence on density of states of the pure tin system, except for causing a widening of the energy gap. Various methods such as ab initio molecular dynamics simulations, the spherical jellium model, adaptive natural density partitioning, localized orbital locator, and electron density difference are employed to analyze the stability of these clusters. The aromaticity of the clusters is examined using iso-chemical shielding surfaces and the gauge-including magnetically induced currents. This study demonstrates that the stability and aromaticity of a tin cage can be systematically adjusted through doping.

A hybrid ZnO/BaTiO3 nano-network for the enhancement of the energy harvesting

Energy-level matching and stress transfer are significant characters of heterojunction to achieve excellent carrier generation and transportation behavior for energy harvesting. Here, we proposed a novel flexible nanogenerator built by ITO/PET layers spin-coated with ZnO/BaTiO3 heterojunction composite, whose electrical output performance can be largely enhanced due to the nano-network constructed by BaTiO3 microspheres and ZnO nanorods. Under periodic stress, varying temperature field and contact-separation conditions, the energy harvesting capacity of ZnO/BaTiO3 nanogenerator is enhanced greatly compared with pure BaTiO3 one, which can be attributed to the improvements of stress and carrier transport efficiency depending on the network structure and energy band matching in ZnO/BaTiO3 heterojunction. The maximum output voltage and current are improved by 6.6 and 4.38 times to 7.2 V and 0.07 μA, respectively, after the polarization treatment by applied electric field, due to the ferroelectric domain rearrangement. While the highest output current reach to 1.0 μA and 2.0 μA for contact-separation and varying temperature modes as TENG and PyENG, respectively. A DFT theoretical result is obtained that electrons accepting/losing capacities of ZnO/BaTiO3 heterojunction are improved with increasing pressure according to the plane-averaged electron density difference. These results indicate that this simply-made multimode nanogenerator can be a promising candidate for energy harvesting under different external excitations.

Insight into properties and reutilization potential of spent polyaniline adsorbents containing transition metals through DFT calculations

Although adsorption technology is an efficient way for removing heavy metal pollutants from wastewater, its widespread application faces challenges related to the disposal and reutilization of hazardous spent adsorbents. Here, we employ density functional theory (DFT) calculations to investigate the properties and reutilization potential of spent PANI adsorbents containing transition metal ions. Bond strength analysis reveals the high stability of spent PANI adsorbents, which is crucial for their safe reutilization. The interaction region indicator (IRI), localized orbital locator (LOL), and decomposition analysis of Wiberg bond order were employed to understand the nature of the bonds between transition metals and imine N atoms. Fukui function analysis indicates that the presence of reducing groups and reductive metal ions in spent PANI adsorbents enhances their chemical stability. The atomic dipole moment corrected Hirshfeld (ADCH) charge and electron density difference (EDD) analysis reveals electron transfers between transition metals and PANI. Moreover, assessments of electrical conductivity, electronic density under electric fields, excited states, and surface charge demonstrate that spent PANI adsorbents hold significant potential for use in energy storage, electrocatalysis, photocatalysis, and environmental pollutant removal. This study provides a molecular-level understanding of the properties and reutilization potential of spent PANI adsorbents.

Ab initio investigation of the competition of pnicogen, halogen, and hydrogen bonds resulting from the interactions between cyanophosphine and hypohalous acids.

The complexes formed as a result of the interactions between cyanophosphine (CP, H2PCN) and hypohalous acid molecules (HOX, X = F, Cl, Br, and I) were studied by employing ab initio computations conducted at the MP2/aug-cc-pVTZ level. Three types of complexes were acquired (I, II, and III) as a result of the (O∙∙∙P) pnicogen bond, the (N∙∙∙H) hydrogen bond, and the (N∙∙∙X) halogen bond interaction, respectively. The results of harmonic vibrational frequency calculations with no imaginary frequencies confirmed the structures as minima. In addition, given the interaction energy of the complexes, hydrogen bond complexes of structure II have the highest stability compared to other structures. In all studied complexes, the strength of the interactions depended on the electronegativity of the halogen atoms. The characteristics and nature of the whole three types of complexes were examined and evaluated with natural bond orbital (NBO), atom in molecules (AIM), molecular electrostatic potential (MEP) maps, non-covalent interaction (NCI) index, and electron density difference (EDD) analyses. The optimization of all complexes and corresponding monomers was conducted through the ab initio method, employing the MP2 level along with the aug/cc-pVTZ basis set for all atoms, except for the iodine (I) atom, for which the aug-cc-pVTZ (PP) basis set was employed. Subsequent frequency calculations were executed to ascertain the minimum energy state of the complexes at the MP2 level and the aug/cc-pVTZ basis set, utilizing Gaussian09 software. The MEP maps of the monomers were generated using the analysis-surface suite (WFA-SAS) software package. To probe the orbital interactions within the studied complexes, NBO analysis was performed employing NBO software. The assessment of bond nature, topological features, and electron density values at critical points for the studied complexes was undertaken using AIMAll software. The NCI index was derived utilizing Multiwfn software, and its three-dimensional representation was rendered using VMD software.

Influence on the mechanical properties and electronic structures of Cu-alloyed Ti5Sn3 compounds from first-principles calculations

First-principles calculations within density functional theory are performed to evaluate the mechanical properties and electronic structures of Cu-alloyed Ti5Sn3 compounds. It was confirmed that the Cu atom prefers to occupy Ti6g site with the lowest site occupation energy. The mechanical properties show that the bulk modulus of Ti5Sn3 can be reduced after Cu alloying. In addition, both the Young's modulus and Poisson's ratio increase and then decrease as the increasing of Cu atoms. The density of states and electron density differences reveal that the replacement of Cu atoms generates new chemical bonds but weakens the p-d orbital hybridization between Ti and Sn atoms, leading to a first increase and then decrease in elastic modulus and hardness.

Evaluate the potential utilisation of B3S monolayer as a novel formaldehyde gas sensor

It is crucial to identify an efficient system for the sensing of formaldehyde (FD). The feasibility of utilising a B3S monolayer (B3SML) detector of FD was evaluated by analysing the adsorption, optical properties, gas-sensing behaviour, and electronic properties of FD and other gas molecules on the B3SML under density functional theory (DFT). The pristine B3SML was found to have satisfactory sensing toward FD molecules. The analysis of the adsorption mechanisms, geometric systems, adsorption energy, electronic and optical properties, charge transfer, and electron density differences revealed that the B3SML could potentially serve as an FD detector. It can be said that the B3SML is a promising sensor for detecting FD molecules. The present study contributes to the existing knowledge of gas-surface interactions and helps develop 2D sensor structures to detect FD gas molecules.

Revealing the mechanism of manganese doping in sulphoaluminate cement clinker

The production of cement clinker from solid waste generated by industrial development is a valid way to reduce the exploitation of natural resources and protect the environment. This paper reports the doping behavior of manganese (Mn) ions in sulphoaluminate cement (SAC) clinker. Results from energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and density functional theory (DFT) simulations indicate that Mn ions enter C4AF by replacing Fe ions, and rarely incorporate into the other two minerals, C4A3S‾ and C2S. Further analysis of the partial density of states (PDOS) and electron density difference (EDD) indicates that the Mn doping mechanism can be ascribed to the comparable electronic contributions of the host and guest ions. These insights into the doping behavior of Mn ions will provide meaningful information to guide the utilization of Mn-containing solid waste as an alternative raw material for the synthesis of SAC clinker.

Engineering functionalized Zr-MOFs as facile removal of indole: Experimental studies and first-principles modeling

Zr-based metal-organic frameworks (Zr-MOFs) are emerging as potential adsorbents for removing nitrogen contaminants in fuel and wastewater. Functionalized Zr-MOFs exhibited superior indole (IND) adsorption capacity than the original MOF, but the activity of the multiple adsorption sites has not been discussed. Through experiment measurement and Density Functional Theory (DFT) calculations, this research investigated the IND adsorption mechanism at various sites on Zr-BDC-NH2 and Zr-BDC-NO2. Based on the adsorption isotherm, the adhesion of IND with Zr-MOFs was determined via the Freundlich model. DFT results suggest that the IND adsorption occurred at highly active sites such as O-linker, μ3-O-cluster, N-amine, and O-nitro via hydrogen and π-hydrogen bonds. Furthermore, the binding energy at each adsorption site in Zr-BDC-NH2 is higher than in Zr-BDC-NO2. In addition to the hydrogen acceptor bond, the π-hydrogen bond has also been analyzed through the electron density difference.

Three‐Dimensional Ionospheric Evolution and Asymmetry of the Electron Density Depletion Generated by the 21 June 2020 Annular Solar Eclipse

AbstractThe three‐dimensional computerized ionospheric tomography (3DCIT) technique has been used to reconstruct the ionospheric response to the 21 June 2020 annular solar eclipse and the results are evaluated by constellation observing system for meteorology, ionosphere, and climate observations. The 3DCIT‐derived electron density (Ne) difference between the eclipse and quiet days showed that the Ne depletion was between 200 and 550 km and the maximum magnitude was about −3.0 × 1011 el/m3 which was at 280 km in altitude. The contributions from below 250 and 350 km altitudes to Vertical Total Electron Content (VTEC) depletion were ∼30% and ∼60%, respectively. Significant asymmetry of Ne depletion with respect to the eclipse path was captured in 3DCIT results, and the deviation conditions between the Ne depletion central line and eclipse path varied at different altitudes. Simulations with the thermosphere‐ionosphere‐electrodynamics general circulation model generally showed consistent ionospheric variations with GNSS (Global Navigation Satellite System) VTEC and 3DCIT electron density. Furthermore, term analysis on the ion continuity equation indicates that the asymmetry of Ne depletion was mainly induced by the neutral wind disturbance which converged toward the eclipse region and caused opposite transport effects on both sides of the eclipse path. The thermospheric composition was also changed by disturbed neutral wind and impacted plasma production and loss rates, contributing to the Ne depletion asymmetry.

Umpolung Isomerization in Radical Copolymerization of Benzyl Vinyl Ether with Pentafluorophenylacrylate Leading to Degradable AAB Periodic Copolymers

AbstractThis study revealed that benzyl vinyl ether (BnVE) shows a peculiar isomerization propagation in its radical copolymerization with an electron‐deficient acrylate carrying a pentafluorophenyl group (PFA). The co‐monomer pair inherently exhibits the cross‐over propagation feature due to the large difference in the electron density. However, the radical species of PFA was found to undergo a backward isomerization to the penultimate BnVE pendant giving a benzyl radical species prior to propagation with BnVE. The isomerization brings a drastic change in the character of the growing radical species from electrophilic to nucleophilic, and thus the isomerized benzyl radial species propagates with PFA. Consequently, the two monomers were consumed in the order AAB (A: PFA; B: BnVE) and the unique periodic consumption was confirmed by the pseudo‐reactivity ratios calculated by the penultimate model: r11=0.174 and r21=6600 for PFA (M1) with BnVE (M2). The pentafluorophenyl ester groups of the resulting copolymers are transformed into ester and amide groups by post‐polymerization alcoholysis and aminolysis modifications. The unique isomerization in the AAB sequence allowed the periodic introduction of a benzyl ether structure in the backbone leading to efficient degradation under acid conditions.

Theoretical insight on the effect of middle layer specifications on electronic properties of SnS2/MX2/SnS2 Trilayer heterostructure (M = Mo, w; X = S, Se, Te)

Recently, the van der Waals (vdW) heterostructure design has gained paramount importance for realizing artificial two-dimensional (2D) material systems with tunable electronic/opto-electronic properties for different technological applications. Driven by this paradigm, in this work, a detailed theoretical analysis has been performed on the structural and electronic properties of different tri-layer van der Waals (vdW) heterostructure of SnS2/MX2/SnS2 (M = Mo, W; X = S, Se, Te) via density functional theory(DFT) based Ab-initio calculation. Moreover, for individual vdW tri-layers, two characteristics of interlayer stacking configurations corresponding to natural stacking configurations of tri-layer SnS2 and MX2 have been considered. The structural properties are evaluated from the interlayer distance, bond angle, bond length, electrostatic difference potential, electron difference density, and Mulliken charge distributions. The electronic properties of different vdW tri-layers are assessed from the interlayer charge transfer, energy band structures, and the density of states profiles, which are quantified from the energy bandgap and effective masses, which are finally compared and benchmarked with homogenous tri-layer SnS2. It has been observed that the chalcogen specification of the middle layer predominantly influences the interlayer interaction and thereby, structural/electronic properties of vdW tri-layers. The vdW tri-layers demonstrate metallic, semi-metallic, and semiconducting energy band structures (bandgap ranging from 0.138 to 0.729 eV, electron effective mass ranging from 0.286/0.286 m0 to 1.299/0.342 m0, hole effective mass ranging from 0.216/0.216 m0 to 2.825/2.927 m0) based on the middle layer MX2 specifications and stacking orientations.

First-principles study of NO adsorption on S vacancy of MoS2 monolayer

Based on first-principles study in this research, a single-layer two-dimensional MoS2 model with intrinsic and a MoS2 with S-site vacancy defects (MoS2-V) were constructed. The adsorption behaviors of NO on the surface of the two models are calculated, and the electronic properties, adsorption energy, and optical properties of the adsorption systems are studied and analyzed. The results of placing NO in different positions of MoS2 show that the adsorption effect is related to the orientation of NO. The adsorption energy of the optimal model for NO adsorbed on intrinsic MoS2 is 0.009 eV, and the adsorption energy on MoS2-V is − 0.304 eV. The forbidden band gap of both adsorption systems are significantly reduced. After NO was adsorbed onto intrinsic MoS2, the forbidden band gap changed from 1.729 eV to 0.235 eV. When NO was adsorbed onto MoS2-V, the forbidden band gap changed from 0.938 eV to 0.201 eV. The band gap change caused by the S vacancy defect leads to the reduction of the electron hopping chance between energy levels. The electron density difference diagrams show that MoS2-V has a stronger adsorption effect on the NO. The total and partial density of states (DOS) of the NO adsorption system shifts to the lower energy region. The dielectric function diagram of the MoS2-V adsorption system is shifted to the low-energy region, and the peak intensity decrease. The reflective index of the MoS2-V adsorb NO system is higher than that of the intrinsic MoS2 in the 0 eV＜E < 1 eV range, indicating that the MoS2-V material enhances the absorption of electromagnetic waves in low-frequency region. The reflective index tends toward zero in the high energy region of these two adsorption systems, indicating they all have strongly absorption of electromagnetic waves in high-frequency region. It is predicted that this material may be applied as a usable adsorption material or developed as a new type of gas material for early warning.

Sensing studies of acenaphthene and acenaphthylene molecules using penta-graphene sheets – A DFT outlook

The emergence of two-dimensional (2D) material leads to fascinating applications. The stability of one of the new allotropes of carbon, penta-graphene is ascertained based on formation energy. The band gap of penta-graphene is witnessed as 1.621 eV, which is confirmed from the band structure. The penta-graphene is used to adsorb two polycyclic aromatic hydrocarbons, namely acenaphthene and acenaphthylene molecules. The adsorption of acenaphthene and acenaphthylene molecules changes the electronic properties of penta-graphene, which is apparent from electron density difference, density of states, and band structure results. Besides, acenaphthene and acenaphthylene molecules are physisorbed on penta-graphene sheets. The outcome shows that penta-graphene can be deployed as a base substrate for the adsorption of acenaphthene and acenaphthylene molecules.

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.

Study of the electronic, optical, elastic and infrared properties of trigonal Mg3As2

Trigonal Mg3As2 is a narrow band gap semiconductor, which makes it possible for many technical applications. However, its fundamental properties, such as electronic, optical, elastic and infrared properties, are still not well studied. Here we systematically studied its these properties with the help of first principles calculations. Band structure is obtained and the origins of the bands are revealed by the calculated partial density of states. Its bonding property is analyzed based on the computed electron density difference and Bader charges. Optical dielectric function and the related quantities are derived and discussed. Its mechanical stability and anisotropy is confirmed by the calculated elastic constants. The phonon vibrational modes in its Brillouin zone center are assigned and infrared emission spectrum is simulated. The reason for the disappearance of one infrared peak in the simulated infrared spectrum is revealed. The brittleness, hardness and melting temperature of this crystal are also predicted. The present study can enrich our understanding of trigonal Mg3As2 and facilitate its future applications.

Copper sulfides (Cu7S4) nanowires with Ag anchored in N-doped carbon layers optimize interfacial charge transfer for rapid water sterilization

There are many methods of water disinfection, and how to realize low energy consumption, high efficiency and safety sterilization has always been a research hotspot. In this work, Cu7S4 nanowires were grown on copper foam, and coated with N-doped carbon layer and Ag particles, which not only improved the conductivity and local field enhancement regions of the material, but also improved the durability and mechanical stability of Cu7S4. DFT (Density functional theory) calculation shows that different kinds of N doping make the electron difference density and work function of the surrounding C different, which leads to high carrier transport capacity at the interface, and Ag anchored in N-doped carbon films can adsorb O2. The band gap of the material is 2.12 eV, and the material has the potential to generate superoxide anion under energy excitation. Under the condition of 6 V voltage and 1000 mL min−1 water flow rate, the long-term water filtration sterilization of high-concentration bacteria can be realized, and the removal efficiency can still reach 99% after 8 h continuous treatment. This work has great application prospects for the purification of highly polluted water in the future.

Hydrogen storage in MXenes: Controlled adjustment of sorption by interlayer distance and transition metal elements

MXene is an attractive solid-state material for high-capacity, secure hydrogen storage under ambient conditions. Controlled adjustment of hydrogen sorption in MXene is essential to improve the storage capability and reversibility at room temperature. This study employed first-principles calculations to investigate the hydrogen sorption properties of multilayered MXenes at the electron level. The strong physical adsorption (Kubas type) of hydrogen was observed in MXene. The interlayer distance and the transition metal elements of MXenes allowed adjustment of the sorption energy of hydrogen. The narrow interlayer space benefited the adsorption of hydrogen molecules, instead of hydrogen atoms. Group 4B elements enhanced the chemical absorption, while Hf2C and Ta2C MXenes possessed relatively strong physical adsorption of hydrogen molecules. Furthermore, the density of states, d-band center, and electron density difference were used to reveal the electronic properties of MXene-hydrogen system.

Engineering In Situ Catalytic Cleaning Membrane Via Prebiotic-Chemistry-Inspired Mineralization.

Pressure-driven membrane separation promises a sustainable energy-water nexus but is hindered by ubiquitous fouling. Natural systems evolved from prebiotic chemistry offer a glimpse of creative solutions. Herein, a prebiotic-chemistry-inspired aminomalononitrile (AMN)/Mn2+ -mediated mineralization method is reported for universally engineering a superhydrophilic hierarchical MnO2 nanocoating to endow hydrophobic polymeric membranes with exceptional catalytic cleaning ability. Green hydrogen peroxide catalytically triggered in-situ cleaning of the mineralized membrane and enabled operando flux recovery to reach 99.8%. The mineralized membrane exhibited a 9-fold higher recovery compared to the unmineralized membrane, which is attributed to active catalytic antifouling coupled with passive hydration antifouling. Electron density differences derived from the precursor interaction during mediated mineralization unveiled an electron-rich bell-like structure with an inner electron-deficient Mn core. This work paves the way to construct multifunctional engineered materials for energy-efficient water treatment as well as for diverse promising applications in catalysis, solar steam generation, biomedicine, and beyond.