Electron Density Difference Research Articles

δ-antimonene nanosheet as a sensing element for ethyl acetate and butyl acetate – a first-principles study

The detection of volatile organic compounds, such as ethyl acetate, and butyl acetate emitted from industries is essential to ensure safety. The two-dimensional (2D) material δ-antimonene nanosheet (δ-SbNS) is used as a base substrate for the detection of ethyl acetate, and butyl acetate vapours. Based on the first-principles investigation, the structural stability and electronic properties of δ-SbNS are determined. The adsorption energy indicates that ethyl acetate and butyl acetate molecules are physisorbed on δ-SbNS. Furthermore, the electron difference density and charge transfer studies reveal the acceptor nature of δ-SbNS. Also, the projected density of states (PDOS) and energy band structure studies upon adsorption of ethyl acetate, and butyl acetate on δ-SbNS are reported. The δ-SbNS behaves as a chemi-resistor owing to adsorption and desorption of ethyl acetate, and butyl acetate vapours.

Theoretical investigation on two-dimensional conjugated aromatic polymer membranes for high-efficiency hydrogen separation: The effects of pore size and interaction

Based on two-dimensional conjugated aromatic polymer (2D-CAP), CAP-1S/CAP-1P monolayers were designed by substituting N with S/P atoms for H2 purification. By using MD and DFT approaches, the H2 purification performance and separation mechanisms of CAP-1S/CAP-1P membranes were investigated. Results showed that ultrahigh H2 permeances of 3.546 × 10−5 and 2.593 × 10−4 mol m−2 s−1 Pa−1 were obtained in CAP-1S/CAP-1P, which were almost 104–105 times larger than the industrially acceptable standard. The selectivities of H2 over CO2/CO/CH4/N2 ranged from 5.719 × 1018 to 3.683 × 1039 in CAP-1S and 4.554 × 1013 to 2.153 × 1033 in CAP-1P. From a statistic viewpoint, the CAP-1S/CAP-1P membranes exhibited complete selectivities of H2 over CO2/CO/CH4/N2. The cohesive energies confirmed the high stabilities of CAP-1S/CAP-1P membranes. The minimum energy pathways, energy profiles, electron density, and charge density difference were analyzed to illustrate the significant impact of precise pore size on the H2 separation performance. From a statistic mechanics view, the interaction between gases and CAP-1S/CAP-1P membranes indicated that the long-range Coulomb interactions dominated the gas diffusion processes. Results of this work highlighted CAP-1P as a promising H2 separation membrane and elucidated the promotion mechanism by fine-tunning pore size and interaction between gases and membranes to balance the H2 permeance and selectivity jointly.

Intermolecular interactions between cyclo[18]carbon and XCN (X = H, F, Cl, Br, I): a theoretical study.

In this article, the intermolecular interactions of cyclo[18]carbon with XCN (X = H, F, Cl, Br, I) were investigated in detail by quantum chemistry calculations and wavefunction analyses. The electrostatic potential and van der Waals potential of cyclo[18]carbon were examined, then the structures of the complexes, the interaction energies of the intermolecular interactions were studied. Quantum theory of atoms in molecules analysis was performed to help understand the specific interactions. The XCN molecules can insert into the cyclo[18]carbon ring, and ClCN, BrCN, and ICN could also bind with cyclo[18]carbon from outside. Charge transfer in the inner complex is more prominent than that of the outer complex. Plots of electron density difference revealed that electron density shift was significantly different when the X atom changed. The main driving force for molecular binding is dispersion attraction, which is disclosed by interaction region indicator analysis and energy decomposition calculations.

Analysis of the adsorption characteristics of gasification pollutants (HCl, COS, H2S, NH3 and HCN) on Ti-anchored graphene substrates

The adsorption characteristics of HCl, COS, H2S, NH3 and HCN (coal gasification pollutants) on the adsorbents (single vacancy, double vacancy, and doped nitrogen atoms) formed by the graphene substrates anchored with titanium atom were analyzed by density functional theory (DFT) calculation. This paper mainly analyzed the geometric configuration of the adsorbent, the adsorption configuration of the gas, and the adsorption energy and the magnetic properties. And through the analysis of the electron density difference and the projected density of states (PDOS), the adsorption mechanism of five coal gasification pollutants on different adsorbents were deeply studied. The calculated results indicate that HCl, COS, H2S, NH3 and HCN can be adsorbed on Ti/SV-N3 graphene adsorbent, and the values of the adsorption energy were −1.07 eV, −1.73 eV, −0.28 eV, −0.41 eV, and -1.23 eV, respectively. Moreover, the introduction of nitrogen atoms significantly enhanced the interaction between single-atom graphene and gas molecules. Based on theoretical results, Ti/SV-N3 was the most suitable for simultaneous removal of these five pollutant gasses, which can guide the development of new materials for pollutant gas removal.

A DFT study of nonlinear optical response of supersalt (Al(BH4)3) doped boron nitride

In the current study, optical and nonlinear optical (NLO) properties of supersalt Al(BH4)3 doped boron nitride (BN) were studied by employing density functional theory (DFT) at the MPW1PW91/6-31 G (d,p) level of theory. HOMO–LUMO energy gap of 7.48 eV was found for pure BN which is reduced to 4.85 eV after doping. Supersalt doping has shown better results on the NLO properties including a decrease in the excitation energy, change in vertical ionization energies, increase in oscillator strength, and increase in dipole moment. Doped molecules have lesser transition energies (ΔE) that lead to higher hyperpolarizability. Electron density difference map was plotted which describes the distribution of electrons of doped compounds. The enhanced values of αiso and βstatic are observed which increases the NLO properties. Overall, the results have shown that supersalt doped boron nitride is an effective approach for designing efficient nonlinear material.

Solution processed edge activated Ni-MoS2 nanosheets for highly sensitive room temperature NO2 gas sensor applications

In this work, we report the effect of nickel incorporation into MoS2 nanosheets for room temperature sensing of NO2 gas. Interestingly, the concentration of Ni (3, 5, 7 at.%) ions plays a vital role in enhancing the morphological and optical properties. The increased edge active sites in nickel incorporated samples play a vital role in high-performance gas sensing. 7 at.% of Ni incorporated MoS2 showed 115% enhancement for 200 ppm of NO2 gas molecules at room temperature, compared to pristine and other concentrations of Ni-incorporated sensors. The enhancement in the gas sensing performance was explained by the possible mechanism. In addition to this, the first principle calculations were performed to identify the influence of Ni-atom into the MoS2 matrix. The electronic structure of the material was tuned by the incorporation of Ni-atom into the MoS2. This was confirmed from electronic band structure, PDOS, electron density difference and Bader charge transfer analyses.

Enhanced non-linear optical response of alkali metal-doped nitrogenated holey graphene (C2N)

In the quest of better non-linear optical (NLO) materials, a DFT method is employed on alkali metals doped C2N to investigate the optoelectronic characteristics. To understand the optoelectronic properties the charge distribution is a key factor for which frontier molecular orbitals (FMOs), transition density matrix (TDM), density of states (DOS), electron density difference map (EDDM) and molecular electrostatic potential(MEP) analyses were carried out. Interaction energy (Eint) is computed to delve into thermodynamic stability. The projected results of all the complexes is lying in domain of effective NLO materials, like constricted EH-L, reduced Eopt, bathochromic shift in ʎmax and above all upgraded α0 and β0. When compared to C2N, doped complexes display extraordinary NLO response with 1st hyperpolarizability ranging from 2.4 × 104 (K@C2N) to 8.02 × 104 a.u. (Li@C2N). Furthermore, alkali metal doping also lessens the energy gap (EH-L)from 2.3 eV to 2.06 eV in Li@C2N. The nature of vibrations and interactions are probed via IR and NCI analysis. Doped molecules (Li@C2N-K@C2N) do possess greater dipole moment (2.48 D to 5.56 D) than C2N (2.04 D). All characteristics support the use of all doped complexes in integrated NLO devices, paving the way for new approach to computational designing of super-efficient NLO materials.

Alkaline earth metals doped C2N with enhanced non-linear optical properties

ObjectiveIn quest of better non-linear optical materials, we investigated optical and NLO (non-linear optical) properties of (C2N) doped with alkaline earthrides (Be, Mg and Ca) designated as C1, C2 and C3, respectively MethodDensity functional theory (DFT) method was used with B3LYP/6–31 G (d, p) level of theory, to carry out geometry optimization and to determine the density of states(DOS), Transition density matrix (TDM), Non-covalent interaction (NCI), infrared (IR) analysis and electron density difference map EDDM. ResultsA significant narrowing of HOMO-LUMO difference gap was observed for every doped molecules with respect to pristine C2N. Bathochromic shift was observed in absorption profile for doped system near-infrared region. Dipole moment (μg) of doped molecules show elevated trend with highest 5.21 D for C2. Polarizability α0 values increased linearly down the group from C1 to C3 while remarkable elevation of first hyperpolarizabilty β0 values was observed, with highest values of 12213.63 au (C1) and 29768.91 au (C2) with basis set 6–31 + +G. Favorable optical and electronic properties of C1 and C2 were observed which suggested them as outstanding candidates for nonlinear optical (NLO) applications.

Revealing boron adsorption on the α-Ti(0001) surface by first-principles calculations

ABSTRACT In this work, the first-principles calculations were performed to discuss adsorption energies, electronic structures, and phase diagrams of boron atoms adsorbed on a α-Ti(0001) surface at different adsorption sites. The adsorption energy, charge transfer, and density of states of the most stable adsorption site were compared and analyzed. As the coverage increases, the adsorption energy and work function increase. After B adsorption, the internal bond length changes significantly, indicating that B adsorption on the α-Ti(0001) surface belongs to chemical adsorption. The density of states and electron density difference confirm that the interaction between B and Ti strengthens with the increase of coverage. These results provide a theoretical basis for the in-depth understanding of the reaction mechanism of B on the α-Ti(0001) surface.

Comparative study on organic solvents and green solvents in separation of aromatic hydrocarbons/low-carbon alcohols azeotrope by structure–activity relationship

Organic solvents, deep eutectic solvents, low transition temperature mixtures and ionic liquids show excellent performance in the separation of azeotropes by extractive distillation. However, the functions and characteristics of four kind of solvents in azeotropic system are not clear. The interaction between solvent molecules and p-xylene and pentanol was studied by quantum chemical calculation, and the separation mechanism was studied at the molecular level. Electrostatic interaction and van der Waals interaction are the key interactions in the complexes. They are quantitatively studied based on the energy decomposition analysis of molecular force field. The electron density difference is used to explain the weak interaction generated by electrostatic interaction. On this basis, the van der Waals potential between solvent and azeotrope molecules is intuitively displayed by using van der Waals potential. The van der Waals potential is suitable for the molecular configuration in which van der Waals interaction plays a key role, which can be regarded as a supplement to the analysis of electrostatic interaction. In addition, since the optimal molecular structure is bound to be accompanied by orbital overlap, the orbital interaction is analyzed by using Natural Bond Orbital; Use the Interaction Region Indicator function to clearly show all types of interactions in one picture. The results of quantum chemical calculation show that the introduction of solvent has a significant effect on the molecular interaction of azeotropes, which is the main factor for the solvent to reduce the relative volatility between azeotropes. This study provides important information for understanding the role of organic solvents, deep eutectic solvents, low transition temperature mixtures and ionic liquids in the separation of azeotropic systems, and has important reference value for the development of new solvents.

Insights into the anisotropic, electronic and magnetism properties of ternary TM2Si2Ys (TM = Cr, Fe, Co, Ni) silicides from the first-principles calculations

In recent years, the transition metal silicides are promising advanced functional materials. However, the relevant physical properties of TM2Si2Ys are not well understood. In this work, the electronic, anisotropic and magnetic properties of SiY, Si2Y, Si3Y5 and TM2Si2Ys (TM = Cr, Fe, Co, Ni) were investigated using the first-principles calculations. The results show that these ternary TM2Si2Y silicides are thermodynamically stable. The elastic properties confirm that these compounds exhibit mechanically stable. According to the elastic constants and elastic modulus results, Co2Si2Y shows the stronger deformation resistance and the brittle behavior. The elastic anisotropy was characterized by the three-dimensional (3D) surface constructions and 2D projections. The band structure, density of states and electron density difference were systematically studied. In addition, the electronic structures explain the magnetic properties for TM2Si2Ys (TM = Cr, Fe, Co, Ni).

Effects of preliminary ion beam treatment of carbon nanotubes on structures of interfaces in МОх/multi-walled carbon nanotube (M =Ti,Sn) composites: Experimental and theoretical study

In this study, ion beam treatment was investigated as a method for functionalizing the surfaces of multi-walled carbon nanotubes (MWCNTs) employed in the production of composites with titanium and tin oxides using magnetron sputtering. Preliminary ion irradiation of MWCNTs obtained a uniform distribution of metal oxides over their surfaces. According to the experimental results, interfacial adhesion in the composites was increased due to the interactions between metal oxides and oxygen-containing functional groups on the surfaces of the MWCNTs. Quantum chemical calculations demonstrated the possibility of M-O-C bonds (M = Ti, Sn) forming with the participation of CO groups fixed on the graphene plane near vacancy-type defects. The features of Ti–O–C and Sn–O–C bonds were investigated based on electron density difference analysis and the density of states of the outer electron shells.

Characteristics of secondary electron emission from few layer graphene on silicon (111) surface

As a typical two-dimensional (2D) coating material, graphene has been utilized to effectively reduce secondary electron emission from the surface. Nevertheless, the microscopic mechanism and the dominant factor of secondary electron emission suppression remain controversial. Since traditional models rely on the data of experimental bulk properties which are scarcely appropriate to the 2D coating situation, this paper presents the first-principles-based numerical calculations of the electron interaction and emission process for monolayer and multilayer graphene on silicon (111) substrate. By using the anisotropic energy loss for the coating graphene, the electron transport process can be described more realistically. The real physical electron interactions, including the elastic scattering of electron–nucleus, inelastic scattering of the electron–extranuclear electron, and electron–phonon effect, are considered and calculated by using the Monte Carlo method. The energy level transition theory-based first-principles method and the full Penn algorithm are used to calculate the energy loss function during the inelastic scattering. Variations of the energy loss function and interface electron density differences for 1 to 4 layer graphene coating GoSi are calculated, and their inner electron distributions and secondary electron emissions are analyzed. Simulation results demonstrate that the dominant factor of the inhibiting of secondary electron yield (SEY) of GoSi is to induce the deeper electrons in the internal scattering process. In contrast, a low surface potential barrier due to the positive deviation of electron density difference at monolayer GoSi interface in turn weakens the suppression of secondary electron emission of the graphene layer. Only when the graphene layer number is 3, does the contribution of surface work function to the secondary electron emission suppression appear to be slightly positive.

Carbonyl sulfide and dimethyl sulfide adsorption studies on novel square-octagon antimonene sheets – A first-principles study

Using the first-principles study, we studied the structural and electronic attributes of square-octagon antimonene nanosheet (so-SbNS). Firstly, the structural and thermal stability of so-SbNS is ascertained. The energy band gap of so-SbNS is recorded as 0.814 eV. Furthermore, the so-SbNS is deployed as base material to adsorb carbonyl sulfide (COS), and dimethyl sulfide (DMS) molecules. The physical adsorption of COS and DMS molecules is noticed on so-SbNS. The so-SbNS behaves as the acceptor of electrons observed from charge transfer and electron density difference results. The band structure and projected density of states changes are noticed due to COS and DMS adsorption on so-SbNS. The results convey that so-SbNS is new material towards the detection of COS and DMS molecules emitted from solid waste.

Enhanced DFT insights of doped phosphorene: Structural and electronic considerations

The electronic properties and structural attributes of doped monolayer phosphorene using density functional theory (DFT) are demonstrated in the present work. The selected dopants are carbon (C), silicon (Si), oxygen (O) and sulphur (S). The band structure and density of states (DOS) analysis indicates transition from semiconducting to metallic nature. Moreover, the electron density and electron difference density spectra also support the above findings. The binding energy for the dopants’ are in the energy range −6 eV to −10 eV affirming feasibility of doping. After doping, the lattice remains undistorted and the associated structural properties are thoroughly investigated based on data analysis backed up with detailed explanations. Dopants impart n-type and p-type characteristics to the phosphorene structure based on their valence electronic configuration. The novel insights of these properties provide us with enhanced perspective of their behaviour and prospective applications. For better understanding, effect of varying concentration of each dopant onto the electronic properties is reported. It includes detailed study of bandstructure, DOS, binding energy and charge transferred of each dopant for each concentration value.

Physisorption of trichloroethylene and tetrachloroethylene on novel zeta arsenene nanotubes – A first-principles study

The structural stability of novel ζ-arsenene nanotubes (ζ-AsNT) is studied based on the density functional theory framework and is used as a base material for the detection of trichloroethylene and tetrachloroethylene vapours. The formation energy of ζ-AsNT is found to be −4.321 eV/atom and the energy band gap is 0.304 eV. Besides, the changes in the electronic properties of ζ-AsNT are explored with regard to the projected density of states, charge transfer, and electron density difference. The bandgap energy decreases for hollow site orientation to 0.205 and 0.204 eV for trichloroethylene and tetrachloroethylene vapours and increases for the valley and top site orientations. The adsorption energies were maximum for the valley site orientation of target molecules onto ζ-AsNT (01.165 and −1.513 eV for trichloroethylene and tetrachloroethylene, respectively). Moreover, the target vapours trichloroethylene and tetrachloroethylene are physisorbed on ζ-AsNT enabling the recycling of base substrate for continuous operation. The average energy gap changes vary from 18 to 32.9% depending on adsorption sites. The variation in the average energy gap owing to adsorption of trichloroethylene and tetrachloroethylene indicates the chemo-sensing nature of ζ-AsNT. The current report lays the inroads in the development of a new sensing element for the detection of chloroethylene molecules.

Femtosecond X-ray Laser Reveals Intact Sea-Island Structures of Metastable Solid-State Electrolytes for Batteries.

Experimental characterization of the nanostructure of metastable functional materials has attracted significant attention with recent advances in computational materials discovery. However, since metastable glass-ceramics are easily damaged by irradiation, damage-free nanoimaging has not been realized thus far. Herein, we propose novel high-contrast coherent diffractive imaging that quantitatively analyzes the intact internal nanostructure of metastable glass-ceramics using femtosecond X-ray pulses. The immersion of sample particles in a solvent helps enhance the reconstructed image contrast and allows us to distinguish an ∼7% electron density difference between an amorphous form and crystals. Furthermore, morphological operations with a band-pass filter quantitatively elucidate the depth information. The evaluated volume ratio of the amorphous to crystalline phases is ∼2.5:1 for the measured metastable (Li2S)70-(P2S5)30 glass-ceramic particle. Sulfide glass-ceramics are used as electrolytes for all-solid-state batteries, which are indispensable for reducing the carbon footprint. Our results will facilitate structural studies on fragile metastable materials with important scientific and industrial implications.

Hydration mechanisms of smithsonite from DFT-D calculations and MD simulations

Investigation on the mineral−water interactions is crucial for understanding the subsequent interfacial reactions. Currently, the hydration mechanisms of smithsonite are still obscure. In this paper, the adsorption of H 2 O at different coverage rates on smithsonite (1 0 1) surface was innovatively investigated using density-functional theory (DFT) calculations and molecular dynamics (MD) simulations by analyzing adsorption model, interaction energy, atomic distance, density of state, electron density difference, concentration profile, radial distribution function and self-diffusion coefficient. We found that single H 2 O preferred to be dissociated on smithsonite (1 0 1) surface via the interaction of surface Zn with the Ow of H 2 O and H-bond between Hw of H 2 O and surface Os. However, dissociation adsorption and molecular adsorption coexisted on the smithsonite surface at a high coverage rate of H 2 O, and dissociation adsorption remained the main adsorption mechanism. Moreover, we found the interaction between smithsonite surface and H 2 O was weakened as a function of H 2 O coverage, which was because the presence of interlayer H 2 O and different layers of H 2 O decreased the reactivity of the smithsonite surface. The H 2 O is mainly adsorbed on the smithsonite surface by forming three layers of H 2 O (about 10–15 Å), with the ordering degree gradually decreasing.

CS2 And H2S adsorption studies on novel hex-star phosphorene nanosheet – a DFT perspective

The adsorption properties of carbon disulfide (CS2) and hydrogen sulfide (H2S) gas molecules on hex-star phosphorene nanosheet (hex-star PNS) are studied. Initially, the structural stability of hex-star PNS is ensured based on phonon band structure and formation energy. The hex-star PNS possesses an energy band gap of 1.393 eV. Besides, upon adsorption of CS2 and H2S on hex-star PNS, the changes in the electronic properties are noticed through electron density difference, band structure, and density of states spectrum. The CS2 and H2S are physisorbed on hex-star PNS, confirming the reversibility of base material. Hence, the results suggest the deployment of hex-star PNS as a sensing substrate toward CS2 and H2S molecules.

Electronic and magnetic properties of the superhalogen Fe(NO3)3 absorbed monolayer MoS2: The regulating performance

The disadvantages of intrinsic MoS2, such as non-magnetic and single carrier-type, may limit its industrial application. A potential technological approach is to regulate its magnetism and carrier mobility. Here, the functionalization of monolayer MoS2 through adsorption of iron-base magnetic superhalogen Fe(NO3)3 is systematically studied by using first-principles theory. The results demonstrate that the interaction between Fe(NO3)3 molecule and monolayer MoS2 is weak. The effect of adsorption on the electronic properties of monolayer MoS2 is analyzed based on electronic band structures, density of states (DOSs) and electron density difference. When Fe(NO3)3 adsorbs on H-MoS2, the band structures of monolayer H-MoS2 and Fe(NO3)3 roughly preserve their independence, thus Fe(NO3)3 can keep its entire magnetic moments. While the adsorption may have a great influence on the electronic properties of T′-MoS2. Moreover, it is found that the Fe(NO3)3 adsorption can regulate the mobility of MoS2, especially the electron mobility of H-MoS2. This study provides a theoretical reference to adjust the electronic properties and magnetism of monolayer MoS2, which may promote its application in electronic devices.