Projected Density Of States Research Articles

Molecular Routes of Dynamic Autocatalysis for Methanol-to-Hydrocarbons Reaction

The industrially important methanol-to-hydrocarbons (MTH) reaction is driven and sustained by autocatalysis in a dynamic and complex manner. Hitherto, the entire molecular routes and chemical nature of the autocatalytic network have not been well understood. Herein, with a multitechnique approach and multiscale analysis, we have obtained a full theoretical picture of the domino cascade of autocatalytic reaction network taking place on HZSM-5 zeolite. The autocatalytic reaction is demonstrated to be plausibly initiated by reacting dimethyl ether (DME) with the surface methoxy species (SMS) to generate the initial olefins, as evidenced by combining the kinetic analysis, in situ DRIFT spectroscopy, 2D 13C-13C MAS NMR, electronic states, and projected density of state (PDOS) analysis. This process is operando tracked and visualized at the picosecond time scale by advanced ab initio molecular dynamics (AIMD) simulations. The initial olefins ignite autocatalysis by building the first autocatalytic cycle-olefins-based cycle-followed by the speciation of methylcyclopentenyl (MCP) and aromatic cyclic active species. In doing so, the active sites accomplish the dynamic evolution from proton acid sites to supramolecular active centers that are experimentally identified with an ever-evolving and fluid feature. The olefins-guided and cyclic-species-guided catalytic cycles are interdependently linked to forge a previously unidentified hypercycle, being composed of one "selfish" autocatalytic cycle (i.e., olefins-based cycle with lighter olefins as autocatalysts for catalyzing the formation of olefins) and three cross-catalysis cycles (with olefinic, MCP, and aromatic species as autocatalysts for catalyzing each other's formation). The unraveled dynamic autocatalytic cycles/network would facilitate the catalyst design and process control for MTH technology.

Mechanistic Insights into Interactions of Polysulfides at VS2 Interfaces in Na-S Batteries: A DFT Study.

Room temperature sodium-sulfur (Na-S) batteries, because of their high theoretical energy density and low cost, are considered as a promising candidate for next-generation energy storage devices. However, the practical utilization of the Na-S batteries is greatly hindered by various deleterious factors such as dissolution of sodium polysulfides (Na2Sn) into the electrolyte commonly termed as "shuttle effect," sluggish decomposition of solid Na2S, and poor electronic conductivity of sulfur. To overcome the challenges, we introduced single-layer vanadium disulfide (VS2) as an anchoring material (AM) to immobilize higher-order polysulfides from the dissolution and also to accelerate the otherwise sluggish kinetics of insoluble short-chain polysulfides. We employ density functional theory (DFT) calculations to elucidate the Na2Sn interactions at the VS2 interfaces. We show that the adsorption strengths of various Na2Sn species on the VS2 basal plane are adequate (1.21-4.3 eV) to suppress the shuttle effect, and the structure of Na2Sn are maintained without any decomposition, which is necessary to mitigate capacity fading. The calculated projected density of states (PDOS) reveals that the metallic character of the pristine VS2 is retained even after Na2Sn adsorption. The calculated Gibbs free energy of each elementary sulfur reduction reaction indicates a significant decrement in the free energy barrier due to the catalytic activity of the VS2 surface. Furthermore, VS2 is found to be an excellent catalyst to significantly reduce the oxidative decomposition barrier of Na2S, which facilitates accelerated electrode kinetics and higher utilization of sulfur. Overall, VS2 with strong adsorption behavior, enhanced electronic conductivity, and improved oxidative decomposition kinetics of polysulfides can be considered as an effective AM to prevent the shuttle effect and to improve the performance of Na-S batteries.

Pressure-induced phase transition in magnetoresistance perovskite La0.75Ca0.25MnO3: a GGA + U study

Density functional theory calculations within a DFT+U approach have been carried out to determine the effect of hydrostatic pressure and strain on the structural, electronic and magnetic properties of La0.75Ca0.25MnO3. We investigate the opportunuty of the appearence of the A-type antiferromagnetic phase under pressure as observed from experiments. At ambient pressure and in the hydrostatic pressure regime (4–25 GPa), the system remains ferromagnetic in its ground state, and the A-type antiferromagnetic coupling is tied to Mn e g orbital order while the ferromagnetic behavior refers to orbital disorder one. No magnetic transition was found when increasing the hydrostatic pressure up to 25 GPa. Applying a tetragonal distortion along the b direction of the pnma orthorhombic structure, the system exhibits a transition from the ferromagnetic orbitally disordered phase to the A-type antiferromagnetic orbitally ordered phase at about 22.5 GPa, in agreement with experiment. Projected density of states (PDOS) calculations predict the pressure and strain effects that are discussed in terms of different electronic occupations through and orbitals.

Highly selective and reversible 2D PtX2 (X = P, As) hazardous gas sensors: Ab-initio study

A first principles characterization has been conducted, in order to inspect the gas sensing mechanism of penta-PtX2 (X = P, As) monolayer, for carbon monoxide (CO), carbon dioxide (CO2), methane (CH4) and ammonia (NH3). Examining the electronic properties, the quantitative and selective nature of the sensing layer has been investigated. The absence of overlapping in projected density of states (PDOS) suggests physical adsorption of the gases by the monolayers. On the basis of Bader charge analysis, the study of charge transfer mechanism suggests that the charge transferred from penta-PtX2 (X = P, As) monolayer to the CO, CO2, CH4 and NH3, is responsible for the gas sensing. The reversibility of both the monolayers has been analysed by studying the relaxation time. In case of PtP2, good amount of reversibility with 0.59 milli-sec for CO and 0.23 milli-sec for NH3, has been observed. The adsorption energies for all the gases are evocative of physical adsorption. The proper amount of adsorption of CO and NH3 with both the sensing layers boasts of their gas sensing efficiency. The variation in the work function of PtP2 and PtAs2, in presence of CO2 is 0.14 eV and 0.17 eV, respectively, making them suitable selections as CO2 gas sensor. The selective nature of PtP2 monolayer towards NH3 was confirmed by analysing the deviation in the I-V characteristics of the monolayer. Based on our findings, both PtP2 and PtAs2 monolayer are potential gas sensors for CO, CO2 and NH3 and can be used to identify gas leaks in factories or manufacturing units.

Chlorobenzene and 1, 4-dichlorobenzene adsorption studies on θ-Arsenene nanosheet – a first-principles analysis

The toxic molecules evolved from sewer causes a threat to humans and animals. The prominent halogenated hydrocarbons, namely chlorobenzene, and 1,4-dichlorobenzene emitted from sewer are considered as target molecules. The adsorption features of chlorobenzene and 1,4-dichlorobenzene on theta arsenene sheets (θ-AsNS) are investigated based on the first-principles study. The adsorption of target molecules on θ-AsNS exhibits physisorption. The alteration in the electronic properties due to chlorobenzene and 1,4-dichlorobenzene on θ-AsNS are noticed with regard to band structure and projected density of states (PDOS) spectrum. The calculations suggest that θ-AsNS is appropriate material to detect the presence of chlorobenzene and 1,4-dichlorobenzene molecules.

Adsorption of SF6 Decomposed Species on Ti3C2O2 and Ti3C2F2 with Point Defects by DFT Study

AbstractThe high specific surface area and electrical conductivity of new 2D metal carbide MXenes make them become a suitable candidate as sensor platform of the gas sensor. Herein, density functional theory (DFT) is implemented to investigate the adsorption of the SF6 decomposed gases (SOF2, SO2, and H2S) on Ti3C2O2, Ti3C2F2, and Ti3C2(OH)2. Modification of the surface of Ti3C2O2 and Ti3C2F2 by O and F point vacancy, respectively, is then performed to improve the adsorption performance. The band structure, charge density differences, electron localization function (ELF), and projected density of states (PDOS) are investigated to study the adsorption mechanism. The results indicate that as compared with the weak adsorption on pristine Ti3C2O2 and Ti3C2F2, the SOF2, SO2, and H2S gas molecules tend to be chemisorbed on Ti3C2O2 and Ti3C2F2 with point vacancy with high adsorption energies. Furthermore, the study of electronic properties suggests that all adsorption systems show high electronic conductivity and the exposed Ti atoms by point defect mainly contribute to the formation of ionic bond with high adsorption energy. Thus, the present results show that Ti3C2O2 and Ti3C2F2 with point vacancy are feasible novel sensing materials to detect SF6 decomposed species with high sensitivity and low electronic noise. The sensitive detection capability of SO2 is particularly noticeable.

Two-Dimensional Single-Atom Catalyst TM3(HAB)2 Monolayers for Electrocatalytic Dinitrogen Reduction Using Hierarchical High-Throughput Screening.

As an environmentally friendly and sustainable strategy to produce ammonia, the electrocatalytic nitrogen reduction reaction (eNRR) is facing the challenge of low conversion rates and high overpotential, to solve which efficient catalysts are urgently needed. Here, a new class of two-dimensional metal-organic layers (MOLs) TM3(HAB)2 (TM = 30 transition metals; HAB = hexaaminobenzene) were evaluated via a three-step high-throughput screening combined with the spin-polarized density functional theory (DFT) method to obtain eligible TM3(HAB)2 catalysts embedded with transition metal atoms from 3d to 5d. Our investigation revealed that Nb3(HAB)2, Mo3(HAB)2, and Tc3(HAB)2 are eligible NRR candidates, among which Tc3(HAB)2 possesses the best catalytic performance with a lowest onset potential of -0.63 V via both distal and alternating pathways and an ultralow NH3 desorption free energy of 0.22 eV. Furthermore, the band structures of three catalysts show their nice conductivity. The corresponding projected density of states (PDOS) illustrate that high catalytic activity can be ascribed to apparent orbital hybridization and charge transfer between catalysts and adsorbed N2. Later, stability and selectivity of all three candidates were computed, Tc3(HAB)2 and Nb3(HAB)2 catalysts are proved to facilitate dinitrogen reduction and exhibit good stability and high selectivity, yet NRR on the Mo3(HAB)2 catalyst is inhibited by hydrogen evolution reaction (HER). Based on the abovementioned studies, we concluded that Tc3(HAB)2 and Nb3(HAB)2 monolayers are promising catalysts for nitrogen fixation. We expect this work to fill the gap of exploring more eligible single-atom catalysts (SACs) anchored with transition metal atoms on MOLs for NRR.

Computational study of H2S adsorption on the pristine and transitional metal-doped phosphorene.

This study aimed to investigate the H2S molecule adsorption on the pristine and X-doped phosphorene (X = first-row transition metal) using DFT+U method. The doping of X atoms on the phosphorene has been evaluated from energetic and electronics aspects. The binding energy values and the results of projected density of states (PDOS) analysis revealed that Ti-, V-, Fe-, and Sc-doped phosphorene have more capability to adsorb H2S molecule in comparison with other systems. Moreover, the cohesive energy values showed that these (Ti, V, Fe, and Sc) doped surfaces are also energetically feasible.

Fe-functionalized zigzag GaN nanoribbon for nanoscale spintronic/interconnect applications

The paper investigated the Zigzag GaN nanoribbons (ZGaNNR) using the density functional theory(DFT) and non equilibrium Green’s function(NEGF) framework. We have calculated the structural, electronic and transport properties of various Fe-ZGaNNR configurations. Based on the binding energy( $$E_{B}$$ ) calculations, Fe-doped@Ga_edge ZGaNNR(-6.51eV) is observed to be most structurally stable among different configurations. Our findings show the substitutional Fe passivation provides a stable bonding as compared to pristine configuration. The magnetic moment of different configurations depends upon the position of Fe atom. The discontinuity is observed in degenerative states of spin modes and same is follows by their respective density of states(DOS) and projected density of states(PDOS). Fe-termination@N_edge ZGaNNR is found to be a strong candidate for magnetic stabilization. High metallicity is observed in Fe-termination@both_the_edges ZGaNNR configuration. Further same is verified through current-voltage characteristics as current follow the pure linear behaviour. The practical application of the work on ZGaNNR can serve as a potential candidate for future low bias nanoscale spitronic devices and low power high speed interconnect applications.

Lead adsorption onto Ni- and Pt-decorated nano γ-alumina: A first-principles study

An efficient computational procedure was proposed to study the adsorption of leadonto two surface decorated alumina nanostructures using density functional theory (DFT) calculations. Notably, lead removal of abundantly available low-price decorated γ-alumina compounds was superior over previously studied functionalized 2D graphene nanosheets. The binding energy for adsorption of Pb on the most stable configuration of γ-alumina was −2.96 eV. Evaluation of adsorption energy demonstrated a noticeable increase in the binding energy of Ni- and Pt-decorated nano γ-alumina as −3.40 eV and −4.29 eV, respectively. Enhanced adsorption energy was taken as a sign of the chemisorption process of Pb on decorated γ-alumina surfaces via covalent bond formation. The use of the projected density of states (PDOS) plot elucidated strong hybridization of Pb 6p with Ni 3d orbitals and 5d orbital of Pt atoms. Moreover, the hybridization of Pb with aluminum 3p and oxygen 2p orbitals proved the strong interaction between Pb and Pt-decorated γ-alumina surface. The results of this investigation can shed some light on decontamination of wastewater applying Ni- and Pt-decorated γ-alumina surfaces. The The proposed approach can also be applied in design and manufacture of iefficient solid adsorbents for the removal of lead contaminations.

Theoretical Study of Transition Metal Dichalcogenides Compound TiS2 and Their Intercalated Compound CrTiS2 Using Density Functional Theory

The Density Functional Theory (DFT) based computational study is carried out for the transition metal dichalcogenides (TMDCs) compound TiS2 and their intercalated 3d transition metal compound CrTiS2. It is carried through Generalized Gradient Approximation (GGA) through Quantum ESPRESSO environment employing Perdew-Burke-Ernzerhof (PBE) exchange and correlation effect with an ultra-soft pseudopotential. In the present work, the structural optimization and electronic properties like energy band structure, density of states (DOS), partial or projected density of states (PDOS), total density of states (TDOS), Fermi surfaces and charge density are reported. The effect of charge transfer from guest 3d transition metal Cr-atom to self-intercalated compound TiS2 has been observed. While, the energy band structure of CrTiS2 compound is computed in the non-magnetic state. From the energy band structure of said materials, we conclude that the TiS2 compound has an indirect narrow band gap though the CrTiS2 compound has an overlapped band structure. The TiS2 shows a semiconductor or semi-metallic nature while doped compound with guest Cr-atom has a metallic material..

Ab-initio calculation of cubic and tetragonal phase of CsPbI3 perovskite

A Study of The CsPbI3 Two-Phase Electronic Structure Has Been Made Through Calculations Using the Density Functional Theory Method. Perovskite metal halide is used as a light-absorbing material on solar cells. This material has a high level of stability and an easy fabrication process. Also, the conversion efficiency has reached 10.1%. The two crystalline phases used are the cubic phase and the tetragonal phase. The electronic structure discussed includes the ribbon electronic curve, as well as the DOS (Density of States) curve, PDOS (Projected Density of States) curve. To find out the electronic structure, and optimization calculation is performed, namely variations in lattice constants, k-points, and cut-off energy. This optimization is done to get the structure with a minimum total energy so that its stability can be achieved. It is known that the bandgap energy value of the CsPbI3 cubic is 1.44eV on the electronic and DOS curve curves. Whereas the band gap energy value of tetragonal CsPbI3 is 0.6 eV on the electronic band curve and DOS as well. This shows that CsPbI3 can be used for the perovskite semiconductor material.

First-Principles Study on the Structural, Electronic, Optical, Mechanical, and Adsorption Properties of Cubical Transition Metal Nitrides MN (M = Ti, Zr and Hf)

Systematic investigation of structural, electronic, optical, mechanical, and adsorption properties of group-IV cubical transition metal nitrides MN (M = Ti, Zr and Hf) is presented in this paper. The structural characteristics, projected densities of states (PDOS), mechanical strength, optical, and adsorption properties have been calculated using first-principles based on density functional theory (DFT). The findings of the comparative and theoretical study showed that, amongst MN, HfN has comparatively higher optical conductivity. Its higher absorption coefficient and least reflectivity ensure the availability of adequate light on its surface. HfN is also found to be more thermally stable with cohesive energy of − 19.112 eV/atom and formation enthalpy of − 5.169 eV/atom. Further, the higher bulk modulus (286 GPa), Young’s modulus (600 GPa), and shear modulus (261 GPa) also ensured its remarkable mechanical strength. Apart from this, the calculated lower adsorption energy (2.3 eV) of H2O molecule over the surface of HfN showed an improved performance in the corrosive environment. The results give a clear indication that HfN may prove as an effective alternative candidate to be utilized in many modern bioelectronics applications.

Investigation of magnetic properties of FeMnP1-xAx (A = In, Se and Sn, where x = 0.33) by use of GGA functionals

Magnetic properties of stable iron-based compounds (FeMnP1-xAx (A = Si, In, Se and Sn) were investigated by use of Quantum Espresso (QE) within the Density Functional Theory (DFT) formalism as a viable magnetic refrigerant. In this research work, DFT technique was the first principle theoretical approach that was employed along with the planewave pseudopotentials (ultrasoft), and the projected augmented wave (PAW) within the generalized gradient approximation (GGA) to describe the electronic structure and investigation of magnetic properties. Magnetic stability is described as the repeated magnetic performance of a material under specific conditions over the life of a magnet. In this case our reference compound, FeMnP0.67 Si0.33 was optimized and its properties were examined in both ferromagnetic (FM) and antiferromagnetic (AFM) states. Two Si atoms were later substituted with atoms of post-transitional metals in period four and five which has shown first-order magnetic transition at near room temperatures. In, Se and Sn were chosen to replace silicon since they would easily mimic the bond, their availability and nontoxic nature. The results showed that only ferromagnetic states of both host and doped compounds gave promising magnetic properties that can be applied in magnetocaloric effect phenomenon. Their band structure results indicated that they were all metals. Antiferromagnetic states showed no magnetic properties as the spin-polarized graph resulted in perfect symmetry of spin up projected density of states (PDOS) and spin down PDOS. From the thermo_pw calculations, it was realized that FeMnP0.67 In0.33 is the best candidate for near room temperature magnetic refrigeration among the studied compounds.

Interaction studies of glycine, acetate and methylamine on β-tellurene nanoribbon – A first-principles analysis

We investigated the structural stability of β-tellurene nanoribbon (β-TeNR) and explored the adsorption behaviour of glycine, acetate, and methylamine malodorous molecules on β-TeNR based on ab-initio calculations. Besides, β-TeNR exhibits semiconducting behaviour with a direct energy gap (Eg) of 1.657 eV. In the beginning, the dynamical solidity and geometrical firmness were confirmed with regard to the phonon band spectrum and negative cohesive energy (−3.406 eV/atom), respectively. With the support of band structure and PDOS (projected-density of states), the electronic characteristics of β-TeNR are explored. Provocatively, two dissimilar superior adsorption sites (top &hollow-sites) of chief malodorous on β-TeNR were demonstrated with regard to the average band gap variation (Ega), Bader charge transfer (Q), and binding energy (EB). The calculated EB of preferential interaction sites is found to be in the scope of −0.190 to −1.751 eV referring to mixed physisorption and chemisorption type of interaction upon β-TeNR. The outcomes recommend that β-TeNR can be positively utilised as a chemi-resistor to sense the glycine, acetate, and methylamine molecules in an unpleasant atmosphere.

Atomic simulation of adsorption of SO2 pollutant by metal (Zn, Be)-oxide and Ni-decorated graphene: a first-principles study.

Due to the impact of toxic gases on human health, considerable interest has been shown in detecting noxious air pollutants, particularly sulfur dioxide (SO2), both experimentally and theoretically. This work provides new insights into the adsorbing (SO2) molecules on the surface of metal-oxide graphitic structures, i.e., Beryllium-Oxide (BeO), Zinc-Oxide (ZnO), and Ni-decorated graphene applying a first-principles study. Computational analyses suggest that the type of binding of SO2 molecule on BeO and ZnO sheets is physisorption so that binding energies of -0.405 and -0.154eV were assigned to ZnO and BeO nanosheets in that order. The adsorption energy of SO2 on metal oxide sheets was much higher than the pristine graphene. Taking pristine graphene as an adsorbent for SO2 molecule, it was found that such nanomaterial is not an efficient adsorbent due to the weak interactions (-0.157eV) and low electron charge transfer (0.042 e) present in SO2/graphene complex. To overcome this issue, graphene nanosheets decorated with nickel atoms were studied for interaction with SO2 molecules; the results indicate that the SO2 molecules were chemisorbed on Ni-decorated graphene sheets with an adsorption energy of -2.297eV. Chemisorption of SO2 molecules on Ni-decorated graphene sheets was proven by the strong orbital hybridization between Ni 3d and sulfur 3p orbitals in the Projected Density of States (PDOS) plot. This work provides useful information about SO2 adsorption on Ni-decorated graphene sheets in order to develop a new class of gas sensing devices. Superior chemisorption of SO2 on Ni-decorated graphene sheets compared to the physical adsorption on BeO and ZnO sheets makes Ni-decorated graphene a potential candidate for detecting SO2 molecules.

First-Principles Calculations of Structural and Electronic Properties of Au-Cu Alloys

This article studies the effect of Au:Cu ratios on the structural properties, electronic structures, and the formation of Au-Cu bulk alloys using density functional calculations. The structural properties are determined by the lattice constants (a, b, c), the crystal systems, and the total energy of the unit cells (Etot). The electronic structures are discussed through band structures, projected density of states (PDOS), and the total density of states (DOS) of materials. The obtained results show, there is an influence of the pseudo-field on the lattice constants of Au, Cu. In which, with the LDA-PWC pseudo-field, the result a = b = c = 4.0910 A with Au, a = b = c = 3.5710 A with Cu, results consistent with the experimental results. When increases concentration of Cu impurity in Au , resulting in the lattice constant of Au: Cu alloy decreases from a = b = c = 4.0910 A to 3.5710 A, the total energy of the cell decreases from Etot = -22952 eV to Etot = -24124 eV, an increase in the electronic density leads to an increase in the conductivity of the Au: Cu alloy. With the obtained results will serve as the basis for future experimental studies.

Study of Structural and Electronic Properties of Intercalated Transition Metal Dichalcogenides Compound MTiS2 (M = Cr, Mn, Fe) by Density Functional Theory

In the present work, we have studied intercalated Transition Metal Dichalcogenides (TMDC) MTiS2 compounds (M = Cr, Mn, Fe) by Density Functional Theory (DFT) with Generalized Gradient Approximation (GGA). We have computed the structural and electronic properties by using first principle method in QUANTUM ESPRESSO computational code with an ultra-soft pseudopotential. A guest 3d transition metal M (viz; Cr, Mn, Fe) can be easily intercalated in pure transition metal dichalcogenides compound like TiS2. In the present work, the structural optimization, electronic properties like the energy band structure, density of states (DoS), partial or projected density of states (PDoS) and total density of states (TDoS) are reported. The energy band structure of MTiS2 compound has been found overlapping energy bands in the Fermi region. We conclude that the TiS2 intercalated compound has a small band gap while the doped compound with guest 3d-atom has metallic behavior as shown form its overlapped band structure.

Ab Initio Calculations on the Structural and Electronic Properties of AgAu Alloys

In our paper, we study the effects of pseudopotential and concentration of Au doping (0, 25, 50, 75, 100%) on the geometric structure and electronic structures of AgAu alloys. For this purpose, we use ab initio quantum calculations in the Material Studios software. The geometric structures of materials are confirmed through the lattice constant, crystal structure, and total energy of the unit cells (Etot). Electronic structures of the materials are confirmed by band gap (Eg), projected density of states (PDOS), and total density of states (DOS). The obtained results show that the pseudopotential and concentration of Au doping on AgAu alloys play an important role in the origin of the physical properties of AgAu alloys.

Electronic and NLO characteristics of small neutral and singly charged iron-doped bismuth clusters

The electronic and optical properties of the iron-doped bismuth nanoclusters having less than 15 atoms are presented here. This doping is especially interesting since it enhances the stability and magnetic properties of the bismuth clusters, as shown here. The effect of singly charging the clusters on their stability and electronic properties is also investigated. Binding energy analysis shows that iron doping enhances the relative stability of the small bismuth clusters. An almost regular pattern is observed for the maximum Raman peak of the first five clusters and the succeeding nine clusters. An oscillating magnetic moment behavior is observed for the neighboring bismuth numbers from 5 to 11. Singly charged clusters also show similar magnetic characteristics. HOMO-LUMO energy gap also follows the expected pattern of the quantum confinement as larger clusters demonstrate the smaller difference between these two levels. Interestingly, this general downward trend falls in the range of visible light. The projected density of states (PDOS) also confirms the obtained results for the energy gap. The charge distribution behavior shows negative charge accumulation on iron atoms except for the case of FeBi.