Principles Density Functional Theory Research Articles

Study on corrosion behavior Ⅱ of hot-dipped Zn-6Al-3Mg alloy coating: Surface oxide layer and ternary eutectic corrosion

The oxide layer and ternary eutectic of Zn–6Al–3Mg alloy coating have an important effect on its corrosion behavior and corrosion resistance, but the influence of oxide layer on the corrosion behavior of the coating and the internal corrosion mechanism of ternary eutectic structure are still unclear. In this study, the oxide layer and ternary eutectic of the coating were characterized in detail, and the corrosion behavior of the oxide layer and ternary eutectic in the environment containing Cl were studied based on first principles of density functional theory. The results show that the surface oxide layer can initially prevent the erosion of Cl-, MgZn2 in ternary eutectic preferentially corrodes after the oxide layer dissolves, corrosion products are formed.

Enhancing hydrogen storage properties of titanium hydride TiH2 with vacancy defects and uniaxial strain: A first-principles study

The structural, electronic, and thermodynamic properties of titanium hydride TiH2 have been investigated using the principles of density functional theory based on the coherent potential approximation (CPA) integrated in the AkaiKKR package, with the aim of reducing the high stability and decomposition temperature to create an ideal material for hydrogen storage, thereby meeting DOE (the U.S. Department of Energy) standard conditions (formation enthalpy ΔH = −40 kJ/mol.H2 and a decomposition temperature Tdes from 289 to 393 K).This study focuses particularly on the effects of titanium vacancy creation and the application of uniaxial deformation on the compound. The results show that with 12% of titanium vacancies, the formation energy increase from −122.34 kJ/mol.H2 to −40.97 kJ/mol.H2 and the temperature of desorption decreases from 936.045 K to 313.49 K, while −8% compressive uniaxial deformation achieve the value −41.42 kJ/mol.H2 and 316.97 K.

Research on optical properties of Eu3+ doped bismuth silicate crystals based on first principles

This paper is based on the first principles of density functional theory and uses the virtual crystal approximation method to calculate and analyze the optical properties of differently proportioned Eu3+-doped Bismuth silicate (Bi4Si3O12, or BSO). The results show that minor Eu3+ doping (1/12–1/3) improves the polarization ability of BSO and reduces energy loss. Additionally, doping an appropriate amount of Eu3+ (1/12–1/3) can improve light absorption and transmission of BSO to some extent. That is to say, Eu3+ doping improves the response of BSO to infrared light, and the absorption capacity in the ultraviolet and visible light regions is also enhanced. The theoretical research in this paper elucidates the changes in the optical properties of BSO after doping with Eu3+, providing a theoretical basis for expanding its application as a scintillation crystal in high-energy physics experiments, nuclear medicine, and other fields.

The Impact of Carbon Corrosion Towards Oxygen Reduction Reaction Activity on Atomically Dispersed M-N-C Catalysts

Atomically dispersed Pt group metal free (PGM free) M-N-C catalysts offer a promising pathway towards a clean energy future.1 This class of materials has proven to be a viable substitute for commercial Pt/C to catalyze oxygen reduction reaction (ORR) with similar activity at only a fraction of the raw material cost.2 To gain a wider market adoption, however, M-N-C catalysts need to significantly improve its durability compared to Pt and its alloys in a real-world operating condition. Towards this end, substantial efforts have focused on making more durable M-N-C catalysts while simultaneously maintaining and improving its ORR activity.3,4 As part of the effort to understand the fundamental aspects that control M-N-C catalysts’ durability during ORR condition, we employ a combined approach using first principles density functional theory (DFT) and density functional tight binding theory (DFTB) to identify the impact of carbon corrosion occurring on M-N-C catalyst towards ORR activity. Our starting atomic representation of the ORR active site is the “C10” type local structure composed of FeN4C10 local defect5 embedded in a monolayer graphene support of varying cell size. As carbon corrosion occurs and consequently creating local carbon vacancies surrounding the active site, we then obtain a family of FeN4C11 and FeN4C12 type of local structures. Our DFT calculations of OH binding energy on these corrosion derived structures suggest that the presence of C vacancies and the subsequent H passivation on dangling C introduces elastic structural deformation to various degree that decreases the theoretical ORR limiting potential. This decrease in DFT calculated ORR limiting potential across a family of FeN4C10, FeN4C11, and FeN4C12 local structures can be attributed to a mechanical energy arising from the surface reconstructions. Reference D. A. Cullen et al., Nat Energy, 6, 462–474 (2021).G. Wu, K. L. More, C. M. Johnston, and P. Zelenay, Science, 332, 443–447 (2011).E. F. Holby, G. Wang, and P. Zelenay, ACS Catal., 10, 14527–14539 (2020).T. Patniboon and H. A. Hansen, ACS Catal., 11, 13102–13118 (2021).H. T. Chung et al., Science, 357, 479–484 (2017).

Metal-ligand transport and optical properties of metal sulfide heterostructure: A density functional theory study

The use of metal sulfides for organic photovoltaics has been a widely studied topic in recent years. The current study reports on the impact of aniline and piperidine ligands on the transport and optical properties of SnS/CoS heterostructure, using the first principles density functional theory approach. The charge transfer properties possess an electropositive and electronegative feature for both the aniline and piperidine ligands, respectively. This charge transfer behaviour is consistent with metal-to-ligand charge transfer properties. The optical properties of SnS/ligand/CoS retain its optical plasmonic transitions for both ligand types, with a corresponding damping effect in the absorption, which suggests interfacial charge transfer-type interactions. Also, an increased density of states for both ligand types is observed, implying increased availability of unoccupied states for electronic transport. These results of ligand-incorporated SnS/CoS suggest its potential for future improved charge transfers in organic solar cells.

Effect of strain on the photoelectric properties of molybdenum ditelluride under vacancy defects: a DFT investigation.

This study explores the impact of deformation on the electrical and optical characteristics of monolayer cadmium telluride (MoTe2) with vacancies, using the foundational principles of density functional theory. It was discovered that both strain and imperfections alter the electrical characteristics of monolayer MoTe2. Under VTe-MoTe2, a direct-to-indirect band-gap transition occurs. In DTe-MoTe2, the band-gap value reduces dramatically, the conduction band changes downward, and the carrier concentration rises. The DVTe-induced band gap state is closer to the Fermi energy level than the VTe-induced band gap state. In this paper, DTe-MoTe2 is chosen for tensile deformation. The results show that the band-gap value tends to decrease by increasing tensile deformation. When the stretching value reaches 10%, the lower bound of the conduction band and the top of the valence band overlap, and the system is converted from a semiconductor to a metal. Considering the density of states, the missing state MoTe2 is mainly contributed by the participation of Te-s, Te-p, and Mo-d orbitals. In terms of optical qualities, the absorption and reflection peaks are red-shifted and blue-shifted, respectively. It is hoped that these effects on the optoelectronic properties will be widely applied. In this study, we utilize the generalized gradient approximation plane-wave pseudopotential method, incorporating Perdew-Burke Ernzerhof (PBE) generalized functions and following the fundamental principles of the density functional theory framework. A 3 × 3 × 1 supercell was constructed as an undoped model based on a MoTe2 monolayer, which consists of 9 Mo atoms and 18 Te atoms. The vacuum flat plate was set to 15Å along the z-direction to avoid interactions between the monolayers. For electronic structure calculations, the energy cutoff was set to 450eV. Each model's computational process and structural optimization were carried out using the Monkhorst-Pack specialized K-point sampling approach. Crystal optimization computations used a 3 × 3 × 1 Monkhorst-Pack K-point grid for molybdenum ditelluride monolayers and a 9 × 9 × 1K-point grid for electronic system analysis, analyzing state density and optical characteristics, respectively. For the structural optimization, the convergence requirements for maximum force, maximum atom displacement, maximum stress, and energy change were defined at 0.03eV/Å, 0.001Å, 0.05 Gpa, and 1.0 × 10-5eV/atom, respectively.

Zigzag boron nitride nanoribbon doped with carbon atom for giant magnetoresistance and rectification behavior based nanodevices

Using the principles of density functional theory (DFT) and nonequilibrium Green’s function (NEGF), We thoroughly researched carbon-doped zigzag boron nitride nanoribbons (ZBNNRs) to understand their electronic behavior and transport properties. Intriguingly, we discovered that careful doping can transform carbon-doped ZBNNRs into a spintronic nanodevice with distinct transport features. Our model showed a giant magnetoresistance (GMR) up to a whopping 105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^5$$\\end{document} under mild bias conditions. Plus, we spotted a spin rectifier having a significant rectification ratio (RR) of 104\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^4$$\\end{document}. Our calculated transmission spectra have nicely explained why there’s a GMR up to 105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^5$$\\end{document} for spin-up current at biases of -1.2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-1.2$$\\end{document} V, -1.1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-1.1$$\\end{document} V, and -1.0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-1.0$$\\end{document} V, and also accounted for a GMR up to 103\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^3$$\\end{document}–105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^5$$\\end{document} for spin-down current at biases of 1.0 V, 1.1 V, and 1.2 V. Similarly, the transmission spectra elucidate that at biases of 1.0 V, 1.1 V, and 1.2 V for spin-up, and at biases of 1.1 V and 1.2 V for spin-down in APMO, the RRs reach 104\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^4$$\\end{document}. Our research shines a light on a promising route to push forward the high-performance spintronics technology of ZBNNRs using carbon atom doping. These insights hint that our models could be game-changers in the sphere of nanoscale spintronic devices.

First-principles calculation of the tunable electronic and optical properties of the BP/ZrS2 heterojunction

s: The first principles of density functional theory (DFT) were used to calculate the geometrical structure, as well as the optical and electrical properties of BP/ZrS2 heterojunctions in this study. The analysis indicates that the BP/ZrS2 heterostructure demonstrates a Z-scheme electron transfer mechanism as a type II heterostructure, and possesses an indirect band gap of 0.19 eV. Under the effect of applied extra electric field and biaxial strain, the BP/ZrS2 heterojunction could undergo a transition from type II to type I and a semiconductor-metal transition. The heterojunction demonstrates markedly enhanced light absorption compared to the two individual monolayers within a specific range of visible light. These features suggest that BP/ZrS2 heterojunctions have a wide range of applications in areas such as photodetectors.

Computational Design of 2D Phosphorus Nanostructures for Renewable Energy Applications: A Review

AbstractElemental phosphorus in its various allotropes has received tremendous research attention recently due to its intriguing electronic and structural properties. Notably, the application of nanostructured materials to overcome the inherent flaws in bulk materials is promising. However, many challenges need to be addressed before its widespread implementation. Thus, a specific tenet to design novel and robust nanomaterials is a decisive factor in the desired outcome, and the most daunting task before realizing this is solving the Schrödinger equation. First principle density functional theory (DFT) calculations have emerged as an insightful and accurate design tool to investigate the structural, electronic, and possible synthesis scenarios of yet undiscovered materials at atomic levels. In this review, the basic principles and the importance of DFT are discussed, followed by a summary of recent advances in the first principle study of elemental phosphorus‐based nanomaterials. Elemental phosphorus‐based nanomaterials and their allotropes have attracted growing interest in the renewable energy community due to their modulable product selectivity. However, the understanding of the physical phenomena of allotropic modification is still lacking. Therefore, the aim is to motivate experimental researchers to conduct DFT studies and experiments to comprehend relevant engineered nanomaterials better. Finally, the challenges and potential future research directions for further theoretical and computational development of phosphorus‐based nanomaterials are outlined.

Mechanism study of H2-plasma assisted Si3N4 layered etch

The cyclic two-step process, comprised of energetic H2 plasma followed by HF wet clean or in situ NF3 plasma, demonstrates Si3N4 layer-by-layer removal capability exceeding 10 nm per cycle, surpassing typical atomic layer etch methods by an order of magnitude. In this paper, we investigated the surface reaction mechanisms via first principle density functional theory simulations and surface analysis. The results unveiled that energetic H2 plasma, in the first step, selectively removes nitrogen (N) in preference to silicon (Si), generating ammonia (NHx) and transforming Si3N4 into SiON upon exposure to air, which becomes removable by HF wet clean in the second step. For the second step employing in situ NF3 plasma, it further leverages H-passivated surfaces to enhance NF3 dissociation and provide alternative reaction pathways to yield volatile byproducts such as SiHF3 and SiFx, thereby significantly improving nitride removal efficiency.

Boron-graphene composite for efficient electromagnetic interference shielding with strong strength and near-zero thermal expansion

The quest for the materials that boast efficient electromagnetic interference (EMI) shielding, strong strength and superb thermal dimensional stability is a burgeoning research area, particularly due to their critical applications in safeguarding sensitive circuits against microwave radiation, especially in the space environments. Graphene-based composites, leveraging the remarkable attributes of individual graphene nanosheets, emerge as prime contenders for fulfilling these sophisticated application requirements. In this study, we prepared boron-graphene composites via spark sintering, combining graphene sheets and boron nanoparticles. This method not only ensures high-performance outcomes but also remains cost-effective and suitable for large-scale production. Boron serves as a binder, facilitating the connection between adjacent graphene sheets and enhancing the graphitization process. The resulting composites demonstrated exceptional electrical conductivity (4.53 × 105 S m−1) and superior EMI shielding effectiveness (average SET 83 dB, with the thickness of 0.25 mm), markedly surpassing previous graphene-based materials in terms of compressive strength (171.3 MPa), and exhibiting low thermal expansion and an ultra-low friction coefficient (0.04). Additionally, to unravel the evolution of boron in the graphene composite and the impact of boron on electrical conductivity, first principles calculations and density functional theory (DFT) were utilized. This investigation underscores the significant promise of boron-graphene composites as high-performance, multifunctional materials across various domains.

The structural, stability, electronic, optical and thermodynamic properties of Ba2AsXO6（X = V, Nb, Ta）double perovskite oxides: A First-Principles study

In this paper, the structural, mechanical, electronic, optical and thermodynamic properties of Ba2AsXO6 (X = V, Nb, Ta) double perovskite oxides have been studied based on the first principles of density functional theory. By calculating some parameters such as Goldsmith’s tolerance factor (tG), octahedral factor (µ), Bartel’s tolerance factor (τ), formation energy, binding energy and elastic constants, it is found that these double perovskite oxides have the potential for stable existence. In addition, Ba2AsXO6 (X = V, Nb, Ta) is an anisotropic material, in which Ba2AsVO6 is brittle, Ba2AsNbO6 and Ba2AsTaO6 are ductile. The electronic properties of the materials show that Ba2AsVO6 and Ba2AsNbO6 are indirect bandgap semiconductors with a band gap of 1.676 eV and 2.654 eV respectively, while Ba2AsTaO6 is direct bandgap semiconductor with a band gap of 3.252 eV. The optical properties revealed that these perovskites exhibit favorable far-ultraviolet light absorption characteristics. The thermodynamic properties show that the specific heat capacity of these double perovskite oxides reaches the Dulong-Petit limit at around 800 K. These results indicate that Ba2AsXO6 (X = V, Nb, Ta) double perovskite oxides have broad application prospects in the fields of thermoelectricity and optoelectronics. Furthermore, these results also provide a valuable theoretical basis for their future experimental synthesis.

First principles modelling of the ion binding capacity of finger millet

Finger millet, a cereal grain widely consumed in India and Africa, has gained more attention in recent years due to its high dietary fibre (arabinoxylan) and trace mineral content, and its climate resilience. The aim of this study was to understand the interactions between potassium (K+), calcium (Ca2+) and zinc (Zn2+) ions and the arabinoxylan structure and determine its ion-binding capacity. Three variations of a proposed model of the arabinoxylan structure were constructed and first principles Density Functional Theory calculations were carried out to determine the cation-binding capacity of the arabinoxylan complexes. Zn2+-arabinoxylan complexes were highly unstable and thermodynamically unfavourable in all three models. Ca2+ and K+ ions, however, form thermodynamically stable complexes, particularly involving two glucuronic acid residues as a binding pocket. Glucuronic acid residues are found to play a key role in stabilising the cation-arabinoxylan complex, and steric effects are more important to the stability than charge density. Our results highlight the most important structural features of the millet fibre regarding ion-storage capacity, and provide valuable preliminary data for confirmatory experimental studies and for the planning of clinical trials where the bioavailability of bound ions following digestion may be tested.

Emerging topological states in EuMn2Bi2: A first principles prediction

New materials with magnetic order driven topological phases are hugely sought after for their immense application potential. In this work, we propose a new compound EuMn2Bi2 from our first principles density functional theory calculations to host novel topological phases such as Dirac/Weyl semimetal and topological insulator in its different magnetic states which are energetically close to one another. The new compound EuMn2Bi2 is found to be dynamically stable from our phonon calculations supporting its experimental preparation in future. By comparing the total energies of various possible magnetic structures of EuMn2Bi2, we identified the ground state. The magnetic ground state is found to be a normal insulator with tiny band gap which is an order of magnitude less than the same in another well studied sister compound EuMn2As2. However, there exist other magnetic states energetically very close to the ground state in EuMn2Bi2 which display remarkable non-trivial band topology such as Dirac/Weyl points close to the Fermi level and topological insulator state driven by magnetic order which is not observed in EuMn2As2. The energetic proximity of these magnetic order driven topological phases makes them tunable via external handle such as magnetic field indicating that the proposed new material EuMn2Bi2 would be a very versatile magnetic topological material if prepared experimentally in future.

Effect of non metallic doping in GeC gas sensors on gas response performance: the first principles study

In this paper, the stability, electronic structure and optical properties of monolayer GeC, B, N and P doped GeC systems are systematically investigated based on the first principles of density functional theory. The results show that the results show that the intrinsic GeC monolayer has a weak adsorption capacity for CH4 and C2H2, which is unfavourable for the sensing and trapping of CH4 and C2H2 gases. Based on calculated adsorption distance, adsorption energy and charge transfer, we find that P-GeC monolayer is the most sensitive to CH4 and C2H2 molecules, and the most of gas molecules act as acceptors to gain electrons from GeC monolayer. The adsorption energy of CH4 is smaller than that of C2H2 gas molecule, which implies that C2H2 is more easily desorbed from P-GeC. Moreover, the work function changes significantly when gas molecules adsorbed on B, N, P-GeC, and Recovery times indicate that B, N and P doped GeC monolayers are more selective and sensitive to C2H2 molecules compared to CH4 molecules. The research work aims to provide a theoretical basis for the application of GeC-based gas sensors, and P-doped GeC monolayers can be used as candidate materials for C2H2 gas sensing and trapping.

Ab-initio study of potassium-based halide perovskites for photovoltaic and opto-electronic applications

A first principle Density Functional Theory (DFT) analysis was applied to investigate the structural, electronic, and optical properties of cubic perovskites KXB3 (X= Ge, Sn; B= Cl, Br). Using the computational code WIEN2K, the corresponding properties have been studied through the use of Generalized Gradient Approximation. Experimental values of lattice constants are consistent with those derived from calculations. The wide direct band gap of 1.5–2 eV (M-M) is confirmed by the electronic band structure. This behavior suggests that the compounds under study are semiconducting KXB3 (X= Ge, Sn; B= Cl, Br) halide perovskite materials are a promising alternative to photovoltaic semiconductors because of their appealing optical properties, as confirmed by a variety of optical properties. Because of their advancement in perovskites, these materials can captivate the world. So, these perovskites materials can captivate world due to its advancement in Opto-electronic application especially in photovoltaic area.

Single atom dispersed tungsten disulfide (WS2) based nanosensors for VOCs detection related to decomposed humans in disaster events

Locating and recovering the victims as a result of disaster events is extremely challenging due to vast search areas, hazardous nature of destroyed infrastructure, and large number of potential victims. An effective avenue for the victim’s detection is through the sensing of human-specific volatile organic compounds (VOCs) emitted both in life and in death. Motivated by this, we employed first principles density functional theory (DFT) calculations to study the sensing properties of pristine, vacancy-induced and single atom dispersed tungsten disulfide (WS2) monolayers towards 11 specific VOCs associated with decomposing humans. We found that pristine, and vacancy-induced WS2 weakly adsorbed the selected VOCs with adsorption energies (Eads) between −0.26 to −0.76 eV. However, the incorporation of selected single atoms of Co, Fe, Nb, and Ni in WS2 improved the sensing properties tremendously. In particular, Nb-WS2 adsorbed the incident VOCs with Eads values of −1.89, −209, −1.43, −0.94, −2.08, −1.57, −1.44, −1.47, −1.70, −1.03, and −2.14 eV for 2-Butanone, benzaldehyde, butanol, heptane, hexanal, methylamine, dimethyl disulfide, dimethyl trisulfide, pyridine, octane, and toluene, respectively, which are ideal for efficient sensing mechanism. Appropriate adsorptions were coupled with the measurable changes in the electronic properties (band gaps) of Nb-WS2, which is essential for proficient sensing. Charge transfer analysis, electro localization functions, electrostatic potentials, and work function calculations further authenticated the sensing propensities of single atom dispersed WS2. Finally, Langmuir adsorption model was employed to explore the sensing at diverse pressure and temperature settings. We believe that these results will help for the development of highly efficient nanosensors for the detection of VOCs related to decomposed humans in mass disaster events. This will increase the detection ability and the chance of locating these victims.

Effects of Alloying Element on Hydrogen Adsorption and Diffusion on α-Fe(110) Surfaces: First Principles Study

Based on first principles density functional theory (DFT) methods, this study employed the Cambridge Serial Total Energy Package (CASTEP) module within Materials Studio (MS) software under the generalized gradient approximation to investigate the adsorption, diffusion behavior, and electronic properties of hydrogen atoms on α-Fe(110) and α-Fe(110)-Me (Mn, Cr, Ni, Mo) surfaces, including calculations of their adsorption energies and density of states (DOS). The results demonstrated that doping with alloy atoms Me increased the physical adsorption energy of H2 molecules on the surface. Specifically, Mo doping elevated the adsorption energy from −1.00825 eV to −0.70226 eV, with the largest relative change being 30.35%. After doping with Me, the chemical adsorption energy of two hydrogen atoms does not change significantly, among which doping with Cr results in a decrease in the chemical adsorption energy. Building on this, further analysis of the chemical adsorption of single atoms on the surface was conducted. By comparing the adsorption energy and the bond length between a hydrogen atom and iron/dopant metal atom, it was found that Mo doping has the greatest impact, increasing the bond length by 58.58%. Analysis of the DOS functions under different doping conditions validated the interaction between different alloy elements and H atoms. Simultaneously, simulations were carried out on the energy barrier crossed by H atoms diffusing into the metal interior. The results indicate that Ni doping facilitates the diffusion of H atoms, while Cr, Mn, and Mo hinder their diffusion, with Mo having the most significant effect, where its barrier is 21.88 times that of the undoped surface. This conclusion offers deep insights into the impact of different doping elements on hydrogen adsorption and diffusion, aiding in the design of materials resistant to hydrogen embrittlement.

A comparative study of NH3 and H2S sensing performance on monolayer nanosheets through first-principle studies

This study investigates the sensing of H2S and NH3 over 2D nanosheets, namely graphene (GRA), boron nitride (BN), silicon carbide (SiC) and boron carbon nitride (BCN), using the first principle density functional theory. A CAM-B3LYP/6–31 G level of theory was used for all the computations and evaluation of the geometric and electronic properties. The optimized clusters indicated the chemisorption between the gas molecules and the SiC nanosheet. The Fourier transform infrared (FTIR) spectra were obtained to study the N-H and S-H shifts in the post-adsorption clusters. Based on the magnitude of the computed adsorption energies, SiC (-0.61 eV for the H2S cluster and −1.21 eV for the NH3 cluster) was found to adsorb both the gas molecules most effectively. The electrostatic potential maps and the molecular orbitals' distribution were studied to investigate the electronic properties. The analysis showed that the adsorption of H2S and NH3 over GRA, BN, and BCN was physical, whereas, on SiC, nanosheet chemisorption was observed. Atom-In-Molecule (AIM) analysis was carried out to account for the possible weak interactions. The study concluded that the SiC nanosheet was the most suitable for the adsorption of H2S and NH3 gases.

Ultrafast Shift Current in SnS2 Single Crystals: Structure Considerations, Modeling, and THz Emission Spectroscopy

AbstractAbove‐band gap optical excitation of non‐centrosymmetric semiconductors can lead to the spatial shift of the center of electron charge in a process known as shift current. Shift current is investigated in single‐crystal SnS2, a layered semiconductor with the band gap of ≈2.3 eV, by THz emission spectroscopy and first principles density functional theory (DFT). It is observed that normal incidence excitation with above gap (400 nm; 3.1 eV) pulses results in THz emission from 2H SnS2 () polytype, where such emission is nominally forbidden by symmetry. It is argued that the underlying symmetry breaking arises due to the presence of stacking faults that are known to be ubiquitous in SnS2 single crystals and construct a possible structural model of a stacking fault with symmetry properties consistent with the experimental observations. In addition to shift current, it is observed THz emission by optical rectification excited by below band gap (800 nm; 1.55 eV) pulses but it requires excitation fluence more than two orders of magnitude higher to produce same signal amplitude. These results suggest that ultrafast shift current in which can be excited with visible light in blue–green portion of the spectrum makes SnS2 a promising source material for THz photonics.