Charge Density Difference Research Articles

Electronic structure, bonding, and mechanical strength at the [formula omitted]-Al2O3 (0001)/L12-Al3Zr (111) interface by first-principles calculations

The interface adhesion energy, interfacial energy, charge density difference, local density of states, and first-principles computational tensile test of α-Al2O3 (0001)/L12-Al3Zr (111) interface were investigated by first-principles calculations. The dominant factors affecting the interfacial bond strength are the type of chemical bonds and the number of electronic orbital hybrids at the interface. The first-principles computational tensile test demonstrates that Al-fcc and Al2-hcp configurations fracture at the interface, while the O-fcc configuration fractures at the Al3Zr slab rather than at the interface and has the best tensile strength. The proposed interface bonding criteria were based on the analysis of the Al2O3/Al3Zr interface bonding data. These criteria will guide the establishment of the interface model. These results will provide theoretical guidance for understanding the failure mechanism of the Al2O3/Al3Zr interface and designing new interfaces.

Acetylene and Ethylene Adsorption during Floating Fe Catalyst Formation at the Onset of Carbon Nanotube Growth and the Effect of Sulfur Poisoning: a DFT Study.

Here, we investigated the adsorption of acetylene and ethylene on iron clusters and nanoparticles, which is a crucial aspect in the nascent phase of carbon nanotube growth by floating catalyst chemical vapor deposition (FCCVD). The effect of sulfur on adsorption was also studied due to its indispensable role in the process and its commonly known impact on metal catalyst poisoning. We performed systematic density functional theory (DFT) computations, considering numerous adsorption configurations and iron particles of various sizes (Fen, n = 3-10, 13, 55). We found that acetylene binds significantly more strongly than ethylene and prefers different adsorption sites. The presence of sulfur decreased the adsorption strength only in the immediate proximity of the adsorbate, suggesting that the effect of sulfur is mainly of steric origin while electronic effects play only a minor role. Higher sulfur coverage of the catalyst surface significantly weakened the binding of acetylene or ethylene. To further investigate this interaction, Bader's atoms in molecules (AIM) analysis and charge density difference (CDD) were used, which showed electron transfer from iron clusters or nanoparticles to the adsorbate molecules. The charge transfer exhibited a decreasing trend as sulfur coverage increased. These results can also contribute to the understanding of other iron-based catalytic processes involving hydrocarbons and sulfur, such as the Fischer-Tropsch synthesis.

Influence of Ga doped CoMo/Al2O3 catalysts on the selective hydrogenation performance of polycyclic aromatic hydrocarbons

It is a challenge to effectively control the intermediate ring hydrogenation products in tricyclic aromatic hydrocracking reactions in order to further increase the selectivity of BTX. A series of doped gallium modified CoMo/Al2O3 catalysts were prepared, the effect of gallium on the catalyst's physicochemical properties, active phase structure and hydrogenation reaction pathway was studied. The study revealed that the doping of gallium species promoted the sulfidation of Mo species and improved the catalytic activity of the catalyst. The 1 % Ga-modified catalyst showed the best selective hydrogenation performance, in which the conversion rate of phenanthrene was up to 83.75 % and the selectivity for dihydrophenanthrene reached 28.60 %. In addition, DFT calculations show that the introduction of Ga into the active phase between the Co and Mo atoms results in a higher differential charge density in the middle ring, which is more conducive to hydrogen adsorption.

First principles study on toxic gas adsorption of PtSe2/GaN heterostructure modified by Cu-group elements

Monitoring and identifying toxic gases is essential due to their detrimental effects on human health and the environment. Consequently, developing high-efficiency sensors for the detection of these harmful gases is of paramount importance. Herein, we present a theoretical study on the adsorption and sensing properties of toxic gases CO, NO and NO2 on intrinsic and Cu, Ag and Au atom-decorated PtSe2/GaN van der Waals (vdW) heterostructures, based on first principles calculation investigations. The adsorption energy, charge transfer, band structures, density of states, charge density difference, electron localization functions and recovery time are analyzed. The findings reveal that the intrinsic system demonstrates weak adsorption capabilities. However, when the surface is modified with elements from the Cu-group, there is a significant improvement in the behavior related to gas adsorption. Particularly, the Ag-decorated system demonstrates optimal gas adsorption performance. Incorporating Ag atoms notably enhances the adsorption energy and the quantity of charge transfer for CO, NO and NO2, thereby promoting a shift from physical to chemical adsorption. This alteration significantly boosts the efficiency of adsorption processes for these gases. As for the recovery time, the decorated systems indicate potential application in gas detection devices and gas adsorbers at various temperatures.

DFT-based adsorption studies of CNCl, HCN, and NH3 on metal-doped diamane

Density functional theory was used to comprehensively investigate the adsorption of cyanogen chloride (CNCl), hydrogen cyanide (HCN), and ammonia (NH3) by metal-doped diamanes. Because the weak gas adsorption ability of pure diamane renders it unsuitable for use as a gas sensor, the adsorption performance thereof was enhanced by doping with alkaline earth and transition metals. The adsorption capacities of monometallic-doped diamanes improved significantly for CNCl, HCN, and NH3. Notably, Be-doped diamane (BeD) delivered the highest adsorption performance for CNCl and HCN, whereas the addition of Au, Ag, and Cu, respectively, to diamane as dopants (AuD, AgD, and CuD) demonstrated enhanced adsorption effects for NH3. The adsorption capacities of the bimetallic co-doped diamanes for CNCl, HCN, and NH3 were significantly enhanced. In particular, diamane co-doped with Cu and Ag (Cu-AgD) exhibited superior adsorption for HCN and NH3, whereas Au and Cu co-doped diamane (Au-CuD) and Au and Ag co-doped diamane (Au-AgD) demonstrated improved adsorption effectiveness for NH3. The charge transfer, band gap, density of states, and charge density differences of these adsorption systems were investigated. Finally, recovery time analysis identified AuD, AgD, CuD, Au-CuD, Au-AgD, and Cu-AgD as potential candidates for reusable sensors.

Cryogenic Photoelectron Spectroscopic and Theoretical Study of the Electronic and Geometric Structures of Undercoordinated Osmium Chloride Anions OsCln- (n = 3-5).

A series of anionic transition metal halides, OsCln- (n = 3-5), have been investigated using a newly developed, home-constructed, cryogenic anion cluster photoelectron spectroscopy. The target anionic species are generated through collision-induced dissociation in a two-stage ion funnel. The measured vertical detachment energies (VDEs) are 3.48, 4.54, and 4.81 eV for n = 3, 4, and 5, respectively. Density functional theory calculations at the B3LYP-D3(BJ)//aug-cc-pVTZ(-pp) level predict the lowest energy structures of the atomic form of OsCln- (n = 3-5) to be a quintet triangle, quartet square, and quintet square-based pyramid, respectively. The CCSD(T)-calculated VDEs and corresponding adiabatic detachment energies agree well with our experimental measurements. Analysis of the corresponding frontier molecular orbitals and charge density differences suggests that the d-orbitals of the transition metal Os play a primary role in the single-photon detachment processes, and the detached electrons originating from different molecular orbitals are distinguishable.

Understanding the Adsorption Mechanism of BTPA, DEPA, and DPPA in the Separation of Malachite from Calcite and Quartz: DFT and Experimental Studies

The relationship between the structure of bis (2,4,4-trimethylpentyl) phosphinic acid (BTPA), diethyl phosphinic acid (DEPA), and diphenyl phosphinic acid (DPPA) on the flotation performance of malachite was investigated. Through a series of flotation experiments, density functional theory (DFT) calculations, and surface analysis methods, we aimed to deeply understand the microscopic mechanism of the interactions between these collectors and the malachite surface. The experimental results showed that BTPA exhibited excellent selectivity and flotation performance for malachite in the pH range of 5.0–11.0, significantly better than DEPA and DPPA. Surface analysis evidence from X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) further confirmed the chemical adsorption characteristics of BTPA on the malachite surface. DFT calculations revealed that the adsorption capacity of BTPA on the malachite surface exceeds that of DEPA and DPPA. Electron transfer analysis, especially through frontier molecular orbital theory, differential charge density, PDOS, and COHP analysis, indicated that the charge transfer process from the s orbitals of oxygen atoms in the collectors to the d orbitals of copper atoms on the mineral surface is the decisive factor for the adsorption strength.

Lattice distortion dependent physical and mechanical properties of VCoNi multi-principal element alloys

Multi-principal element alloys (MPEAs) have garnered widespread recognition owing to their remarkable mechanical properties. Among alloying elements, the vanadium (V) element exhibits unique characteristics and has a high strengthening effect in the face-centered cubic Co-Ni-V MPEAs family owing to its large atomic radius. Here, first-principle calculations are utilized to examine the physical and mechanical characteristics of extensively researched VCoNi MPEAs. The objectives of this work are to give guidance on the design of MPEAs with desirable capabilities and fresh insight for understanding the role of lattice distortion described by atomic size difference on lattice parameters, binding energy, generalized stacking-fault energy, elastic properties, and electronic properties. A high degree of lattice distortion can lead to an increase in lattice constants, a more stable structure, and enhanced plasticity. These trends are attributed to a shortened pseudo-energy gap, large variations in charge density difference, and compact band overlap with increasing lattice distortion. The above results aim to serve as a point of reference for exploring the physical and mechanical attributes of MPEAs.

Selective adsorption behavior of reducing gases on the NiO–In2O3 heterojunction under the interfacial effect

Gas sensors with the p–n heterojunction have demonstrated distinct sensing responses to reducing gases, yet a clear understanding of the reaction pathways and selective adsorption mechanisms for specific gas components remains elusive, impeding practical applications. In this study, we constructed an atomic-level NiO–In2O3 heterojunction and explored its adsorption behaviors and sensing properties for CO and H2 by first-principles calculations. Analysis of its electronic properties, focusing on binding energy, differential charge density, and density of states, confirmed the creation of a highly stable NiO–In2O3 heterojunction and alterations in the coordination environment of the surface-active atoms. These changes potentially led to differences in the affinity between the gas molecules and the adsorption sites. The calculations of the adsorption properties revealed that the adsorption capacity of H2 is relatively weak compared to the strong interactions between CO and heterojunction surface atoms, indicating a readily variable reaction pathway for H2. Consequently, the adsorption configuration at the interface site on the NiO–In2O3 heterojunction surface exhibited a predominantly p-type response for CO and a unique n-type response for H2. This interfacial effect of the heterojunction is crucial for the selective adsorption of CO and H2. Furthermore, the opposite response signal was verified by gas sensing tests, which also presented the superior stability of the NiO–In2O3 sensor. The p–n heterojunction of the corresponding composites was effectively characterized. This research offers new insights into the selective adsorption mechanism, paving the way for the development of gas sensors.

Adsorption of NH3, HCHO, SO2, and Cl2 gasses on the o-B2N2 monolayer for its potential application as a sensor

The adhesion behaviour of the o-B2N2 monolayer (OBNML) onto the toxic gasses, namely NH3, HCHO, SO2, and Cl2, was scrutinized through DFT. The adhesion attributes, stet density, differential charge density and the optimal structure of the adhesion systems were investigated, and the findings indicated the stability of the OBNML. Furthermore, to further investigate the gas adhesion attributes, the workfunction, sensitivity, recovery time (RT) and the energy gap were examined. Based on the results, the optimal RT for the OBNML at high temperatures was easier, and the higher sensitivity and the more change in the workfunction also reflected the better adhesion capability of the OBNML. The findings also showed that the OBNML was capable of acting as an adsorbent of these toxic gasses, and it can be useful in practically purifying the air and protecting the environment.

Theoretical insights into interface effects on CO2 hydrogenation to methanol over In4O6/ZrO2(1 1 1) catalyst

Methanol synthesis from CO2 hydrogenation on the defective In4O6/ZrO2(111) surface with surface oxygen vacancies has been investigated by using periodic density functional theory calculations. The calculated oxygen vacancy formation energies indicate that the D1 surface with Ov1 defective sites on the surface of the In4O6 clusters is thermodynamically the most favorable for the adsorbed CO2 to generate methanol along the HCOO pathway. In contrast, the D4 surface with Ov4 defect sites at the interface is the most unstable, reacting along the RWGS path on clusters near the Ov4 defects, and hydrogenating along the HCOO path at the interfacial position to generate methanol. The differential charge density curves further reveal the close relationship between the electronic structure of the metal oxide interface and the CO2 hydrogenation mechanism to methanol.

Adsorption of LIBs Thermal Runaway Gases on TM-Decorated HfS2 Surface: A DFT Study.

With the wide application of lithium-ion batteries (LIBs) in different fields, safety accidents occur frequently. Therefore, it is necessary to monitor the thermal runaway gas for an early warning. In this article, the adsorption properties of the characteristic gases of LIBs thermal runaway gases are studied by density functional theory (DFT). The adsorption structure of TM (Co/Rh/Ir)-decorated HfS2 (TM@HfS2) is established, and its adsorption properties for C2H4, CH4, and CO are studied. The adsorption energy, charge transfer, band, DOS, charge difference density, work function, and recovery time are discussed in detail. The results show that Ir@HfS2 has the strongest adsorption performance for C2H4 and CO, so C2H4 and CO can be stably adsorbed on the surface of the Ir@HfS2 monolayer. The adsorption energy of CH4 on Co@HfS2 is stronger than those of Rh@HfS2 and Ir@HfS2, but the adsorption energy is still very small. By applying biaxial strain to Co@HfS2, we found that the adsorption energy increases with the increase in negative strain. This study provides a theoretical basis for the regulation of the adsorption properties of HfS2 by different transition metals.

Two-Dimensional Transition Metal Phosphides As Cathode Additive in Robust Lithium-Sulfur Batteries.

The development of advanced cathode materials able to promote the sluggish redox kinetics of polysulfides is crucial to bringing lithium-sulfur batteries to the market. Herein, two electrode materials: namely, Zr2PS2 and Zr2PTe2, are identified through screening several hundred thousand compositions in the Inorganic Crystal Structure Database. First-principles calculations are performed on these two materials. These structures are similar to that of the classical MXenes. Concurrently, calculations show that Zr2PS2 and Zr2PTe2 possess high electrical conductivity, promote Li ion diffusion, and have excellent electrocatalytic activity for the Li-S reaction and particularly for the Li2S decomposition. Besides, the mechanisms behind the excellent predicted performance of Zr2PS2 and Zr2PTe2 are elucidated through electron localization function, charge density difference, and localized orbital locator. This work not only identifies two candidate sulfur cathode additives but may also serve as a reference for the identification of additional electrode materials in new generations of batteries, particularly in sulfur cathodes.

Theoretical study of the adsorption properties of transition metal atom-doped monolayer GeSe materials for SF6 decomposition components

The insulating gas SF6 will decompose and generate a series of by-products under fault conditions, affecting the power equipment's stable operation. In this paper, the adsorption characteristics of the two-dimensional material GeSe and doped with transition metal(TM) on SF6 decomposition gases HF, CS2, and SO2F2, including adsorption energy, charge transfer, density of states, and differential charge density, are investigated based on the First-principles, and their potentials to be used as a gas-sensitive material for monitoring SF6 decomposition are analyzed based on theoretical response heights and recovery times. The results show that the doping of TM atoms enhances the adsorption capacity of GeSe materials for SF6 decomposition components, in which Co-GeSe materials can be used to monitor the production of CS2 gas molecules. In contrast, Mn-GeSe materials have a promising prospect as adsorbents for SO2F2.

Multi-layers hexagonal hole MXene trap constructed by carbon vacancy defect regulation strategy enables high energy density potassium-ions storage

Due to the slow reaction kinetics of potassium-ions with large size radius in layered materials, the energy density of aqueous potassium-ion hybrid supercapacitors (PIHCs) is severely limited. At the same time, the treatment of defects is a “double-edged sword” in energy storage materials, which requires targeted and precise regulation. In order to solve this problem, multi-layers hexagonal hole MXene trap was constructed by using the carbon vacancy defect regulation strategy, and high specific capacitance and energy density potassium-ion storage was realised in PIHCs. The structure-activity relationship at the atomic level was elucidated in combination with the pseudo-capacitance effect caused by the change of valency of newly exposed titanium atoms in the inner wall of the hexagonal hole MXene trap. By density functional theory, the adsorption energy and kinetic analysis of multi-layers hexagonal hole MXene for potassium-ions were calculated, and the optimal position and quantity of potassium-ions were determined. By quantitative analysis of electron band structure and differential charge density, the internal mechanism of high conductivity and energy density of multi-layers hexagonal hole MXene PIHCs was revealed.

The dual-transition-metal dichalcogenide monolayers anchored with Mn dimer: Promising electrocatalysts for efficient nitrogen reduction reaction

Due to its great efficiency, the electrocatalytic nitrogen reduction reaction (NRR) presents itself as a viable and eco-friendly substitute for the traditional Haber-Bosch ammonia production process. However, it is still a formidable task to find electrocatalysts with high activity and selectivity. In this study, a series of transition metals (TM = Ti–Ni, Zr–Mo, Ru–Pd, and Hf–Pt) anchored on 1T′-dual-transition-metal dichalcogenides (1T′-d-TMDs) monolayers (TM2@1T′-CrCoS4) were systematically investigated as electrocatalysts for NRR using first-principles calculations based on density functional theory. Based on a thorough examination of selectivity, high activity, and stability, Mn2@1T′-CrCoS4 and Co2@1T′-CrCoS4 demonstrate exceptional NRR performance. With a limiting potential of −0.11 V, Mn2@1T′-CrCoS4 stood out among them in terms of catalytic activity, favoring the enzymatic pathway. Furthermore, ab initio molecular dynamics (AIMD) simulations were used to assess the dynamic stability of Mn2@1T′-CrCoS4 and Co2@1T′-CrCoS4. To determine the source of increased activities, the density of states (DOS), charge density difference, and crystal orbital Hamilton population analysis were used. According to our research, the 1T′-d-TMDS is a viable substrate for the development of effective NRR catalysts and offers a platform for electrocatalyst experimentation.

Highly efficient photocatalytic performance of Z-scheme BTe/HfS2 heterostructure for H2O splitting

Constructing van der Waals (vdW) heterostructures is one of the effective strategies for developing highly efficient photocatalysts. In this study, we have designed a novel BTe/HfS2 heterostructure and systematically investigated its electronic properties and photocatalytic performance using first-principles calculations. The dynamic stability and thermodynamic stability of the heterostructure are verified through phonon spectrum simulations and ab initio molecular dynamics (AIMD) simulations, respectively, enhancing the likelihood of experimental synthesis. The bandgap of the BTe/HfS2 heterostructure is 0.12 eV, and the band edge positions satisfy the overall water splitting requirements for photocatalysts. The charge density difference, work function, Bader charge, and band alignment all confirm that the BTe/HfS2 heterostructure is a typical direct Z-scheme heterostructure, effectively facilitating the separation of photogenerated charge carriers and exhibiting strong redox capability. The solar-to-hydrogen (STH) efficiency of the BTe/HfS2 heterostructure reaches as high as 17.32 %. Moreover, the heterostructure exhibits strong light absorption capability, reaching a magnitude of 105. The carrier mobility of the BTe/HfS2 heterostructure surpasses that of two individual monolayer materials, with the hole mobility in the x-direction reaching an impressive 28357.15 cm2s-1V-1. Simultaneously, the Gibbs free energy indicates that the BTe/HfS2 heterostructure can undergo the hydrogen evolution reaction (HER) with only 0.19 eV of external potential at pH = 0. Moreover, at pH = 7, it can spontaneously convert H2O into O2. Therefore, the newly designed BTe/HfS2 heterostructure offers a new direction for practical applications of photocatalysts.

Hydrogen bond-assisted construction of MOF/semiconductor heterojunction photocatalysts for highly efficient electron transfer

It remains challenging for the fabrication of metal-organic framework (MOF)/semiconductor heterojunction photocatalysts with close contact interfaces. In this work, a novel MOF/semiconductor heterojunction photocatalyst consisting of H2O2-modified TiO2 nanotubes (H2O2-TNTs) and MIL-88B(Fe)-NH2 (labeled as H-T/M) was firstly constructed based on the hydrogen-bonded combination between the O atoms from –OOH groups resulting from H2O2 absorbed on the surface of TiO2 nanotubes and the H atoms of the –NH2 group in MOF. The significantly enhanced photocatalytic property of the H-T/M heterojunction for reducing Cr(VI) could be ascribed to the accelerated interfacial electron transfer dynamics by a channel of hydrogen bonds (N···H–O–O–Ti), which could be extracted from the femtosecond transient absorption spectroscopy (fs-TAS). Moreover, the built-in electric field and the differences in charge density based on density functional theory (DFT) calculations could provide the driving force for charge transfer.

GO-based membranes with enhanced stability and permeability by implanting etched-MXene nanosheets: The role of binding energy in stabilizing 2D membranes

Graphene oxide (GO) stands out as a promising choice for the construction of next generation nanofiltration membranes in wastewater purification. Nevertheless, achieving the requisite stability and optimal permeability for effective separation of aqueous molecules and ions poses a formidable challenge for graphene oxide membranes. In this study, a series of GO/etched-MXene membranes with markedly enhanced stability and permeability was fabricated to provide high-level performance. Due to seemly etching process, the optimal GO/etched-MXene membrane featured additional nanochannels for faster mass transfer, consequently evincing a high water permeance of 88.2 ± 3.8 L m−2 h−1 bar−1 with an excellent dye/salt separation efficiency (CR/NaCl selectivity = 22.6, CR/Na2SO4 selectivity = 42.0). Noticeably, the introduction of etched-MXene nanosheets demonstrated a pronounced enhancement in stabilizing the GO membrane within aqueous environment. The density functional theory (DFT) calculations showed that the binding energy of MXene nanosheets (−7.68 eV) was significantly larger than GO nanosheets (−1.11 eV). According to charge difference density results, compared with GO nanosheets, the electrons transfer in MXene nanosheets was more concentrated. As a result, the specially-designed GO/etched-MXene membranes could maintain a stable separation performance during crossflow filtration, while the pristine GO membrane rapidly cracked. This approach is anticipated to establish a theoretical framework for comprehending the contribution of nanosheet binding energy in stabilizing two-dimensional membranes, fostering synergistic advantages in the advancement of GO membranes characterized by both elevated water permeance and requisite stability in water treatment.

Exploring optoelectronic and thermal characteristics of Janus MoSeTe and WSeTe monolayers under mechanical strain

This paper reveals the effect of external strain on the electronic, thermal and optical properties of Janus MSeTe (M=Mo, W) using first principles. Phonon spectrum calculations confirm the dynamic stability of the system. Biaxial stretching can effectively modulate its thermal properties. Uniaxial, biaxial and shear strains modulate the band structure, structural parameters, averaged differential charge density and optical properties of the MSeTe system to different degrees. The increase of compressive and shear strains leads to a gradual decrease of the band gap and triggers a semiconductor-metal phase transition at the critical point. The intrinsic system exhibits strong light absorption in the visible and ultraviolet regions, while strain induces a redshift of the light-absorbing edge, which enhances the response to the infrared and visible wavelength bands. These findings provide a theoretical basis and application potential for the design of optoelectronic devices and thermoelectric materials.