Density Functional Theory-based First-principles Research Articles

First-principles study of hydrogen sulfide decomposition on Sc-Ti3C2O2 single-atom catalyst.

Hydrogen sulfide gas poses significant risks to both human health and the environment, with the potential to induce respiratory and neurological effects, and a heightened fatality risk at elevated concentrations. This article investigates the catalytic decomposition of H2S on a Sc-Ti3C2O2 single-atom catalyst(SAC) using the density functional theory-based first-principles calculation approach. Initially, the adsorption behavior of H2S on Ti3C2O2-MXene was examined, revealing weak physical adsorption between them. Subsequently, the transition metal atom Sc was introduced to the Ti3C2O2 surface, and its stability was studied, demonstrating high stability. Further exploration of H2S adsorption on Sc-Ti3C2O2 revealed direct dissociation of H2S gas molecules into HS* and H*, with HS* binding to Sc and H* binding to O on the Ti3C2O2 surface, resulting in OH groups. Using the transition state search method, the dissociation of H2S molecules on the SAC's surface was investigated, revealing a potential barrier of 2.45eV for HS* dissociation. This indicates that the H2S molecule can be dissociated into H2 and S with the action of the Sc-Ti3C2O2 SAC. Moreover, the S atom left on the catalyst surface can aggregate to produce elemental S8, desorbing on the catalyst surface, completing the catalytic cycle. Consequently, the Sc-Ti3C2O2 SAC is poised to be an efficient catalyst for the catalytic decomposition of H2S. The Dmol3 module in Materials Studio software based on density functional theory is used in this study. The generalized gradient approximation method GGA-PBE is used for the exchange-correlation function. The complete LST/QST and the NEB methods in the Dmol3 module were used to study the minimum energy path of the dissociation of hydrogen sulfide molecules on the catalyst surface.

Evaluation of Structural, Electronic, Optical and Mechanical Properties of Na-based Oxide‐Perovskites NaXO3 (X = Co, Be, Ba): A DFT study

Here, we employed density functional theory-based first-principles computations to examine the structural, electrical, optical, and mechanical properties of NaXO3 (X = Co, Be, Ba) materials. The ideal lattice constants for each of the three materials were fitted using the Birch-Murnaghan method. These compounds have cubic structures with Pm3m-221 space group. According to investigations of the energy band distributions, all of these compounds have indirect band gaps. Calculations also show that NaCoO3 and NaBaO3 compounds have wide bandgap semiconductor properties, while NaBeO3 shows an insulator performance. The degree of electron localization in particular bands is confirmed by TDOS and PDOS. These compounds absorb light more strongly in the ultraviolet region. We discovered that all of these compounds have a mixture of ionic and covalent bonding behavior. We also discovered that the mechanical stability of each of the compounds is simplified by their cubic shapes. These findings not only advance our knowledge of NaxO3 compounds but also create new opportunities for the materials' possible use in a variety of technological contexts. Additionally, these results offer a theoretical foundation for additional experimental research on these materials.

Modulation of the optical and transport properties of epitaxial SrNbO3 thin films by defect engineering

The discovery of strontium niobate (SNO) as a potentially new transparent electrode has generated much interest due to its implications in various optoelectronic devices. Pristine SNO exhibits exceptionally low resistivity (∼10−4 Ω cm) at room temperature. However, this low resistivity occurs due to large number of carrier concentration in the system, which significantly affects its optical transparency (∼40%) in the visible range and hinders its practical applications as a transparent electrode. Here, we show that modulating the growth kinetics via oxygen manipulation is a feasible approach to achieve the desired optoelectronic properties. In particular, epitaxial (001) SNO thin films are grown on (001) lanthanum aluminate by pulsed laser deposition at different oxygen partial pressures and are shown to improve the optical transparency from 40% to 72% (λ = 550 nm) at a marginal cost of electrical resistivity from 2.8 to 8.1 × 10−4 Ω cm. These changes are directly linked with the multi-valence Nb-states, as evidenced by x-ray photoelectron spectroscopy. Furthermore, the defect-engineered SNO films exhibit multiple electronic phases that include pure metallic, coexisting metal-semiconducting-like, and pure semiconducting-like phases as evidenced by low-temperature electrical transport measurements. The intriguing metal-semiconducting coexisting phase is thoroughly analyzed using both perpendicular and angle-dependent magnetoresistance measurements, further supported by a density functional theory-based first-principles study and the observed feature is explained by the quantum correction to the conductivity. Overall, this study shows an exciting avenue for altering the optical and transport properties of SNO epitaxial thin films for their practical use as a next-generation transparent electrode.

Exploring the Impact of Zirconium Doping on the Mechanical and Thermodynamic Characteristics of Pt-40Rh Alloy through First-Principles Calculations

Zirconium (Zr) element doping has proven to be an effective strategy for reinforcing the strength and toughness of Pt-Rh alloys. However, the incorporation of Zr into Pt-Rh alloy in solid solution form renders its microstructural observation challenging through experimental means, thus complicating the elucidation of its underlying mechanisms. Therefore, this study employs density functional theory-based first-principles calculations to investigate the mechanical and thermodynamic properties of Pt-40Rh-xZr (x = 0, 0.1, 0.5, 1.0) alloys. The results reveal that with an increasing Zr weight percentage, Young’s modulus, and hardness of Pt-40Rh-xZr alloys exhibit a trend of an initial decrease followed by a subsequent increase. Notably, at a Zr weight percentage of 1.0 wt.%, the alloy Pt-40Rh-1.0Zr demonstrates the highest Young’s modulus (329.119 GPa) and hardness (10.590 GPa). Concurrently, thermodynamic calculations indicate that as Zr content increases, the crystal thermal stability of Pt-40Rh-xZr alloys initially decreases before rising again. More specifically, the coefficient of thermal expansion for Pt-40Rh-1.0Zr is merely 89.518% of that observed in Pt-40Rh. These results imply that incorporating 1.0 wt.% Zr results in the most substantial enhancement in the comprehensive mechanical properties of the Pt-40Rh-xZr alloy. Consequently, this study offers theoretical insights that can guide the extended application of Pt-Rh alloys.

Pressure-induced physical properties of alkali metal chlorides Rb2NbCl6: A density functional theory study

Using density functional theory-based first-principles simulations, detailed physical properties of the tetragonal phase alkali metal halide Rb2NbCl6 under pressure were explored for the first time. The structural, mechanical, and thermodynamic stability were confirmed by the Born stability requirements and the negative values for the formation energy. The analysis of Pugh’s and Poisson’s ratios and Cauchy’s pressure reveals that Rb2NbCl6 is ductile under the pressures in consideration. As the applied pressure rises, the elastic moduli show a rising trend, which indicates that Rb2NbCl6 stiffens up. According to several anisotropy indices, the compound is noticeably anisotropic both in ambient and under pressure. The machinability index suggests that the material under study is highly machinable. Several mechanical features of Rb2NbCl6 are analyzed according to the results of elastic constants and adequately explained. Since the melting temperature rises with applied pressure, Rb2NbCl6 is more suitable for high-temperature applications. The computed total density of states (TDOS) at 0 GPa pressure at EF is ∼5.07 states/eV/f.u., and applied pressure has a negligible effect on the value of DOS. The study of electronic properties provides significant support for interpreting the optical function. As the applied pressure rises, the reflectivity and absorption spectra shift to higher energy regions. High-reflectivity spectra suggest that the material would be an excellent choice for coatings that lower solar heating. The authors of this study expect that the fascinating findings of this investigation will give researchers and engineers a helpful foundation.

Alkaline earth based antiperovskite AsPX3 (X = Mg, Ca, and Sr) materials for energy conversion efficient and thermoelectric applications

Antiperovskite were created by swapping ionic positions in the perovskite ABX3 crystal composition. These have great potential for renewable energy devices owing to their low band gap, low cost, and high absorption with Pm-3m space group. Herein, the authors have investigated inherent properties such as bulk modulus and its pressure derivatives, lattice constant, the density of states, band gap, effective mass, refractive index, dielectric constant, extinction coefficient, and absorption coefficient, thermoelectric parameters etc of antiperovskite materials by using density functional theory-based first-principles calculations. These materials exhibit high absorption in the Visible, Ultraviolet region and also in the Near Infrared region which is the most admirable property acquired by various Optoelectronic devices. The proposed compounds have been found mechanically and thermodynamically stable. Their high figure of merit makes them a potential candidate for thermoelectric devices. The proposed material AsPCa3 with a theoretical efficiency of 34% is expected to be a good photovoltaic absorber material.

An atomistic modeling study of high-throughput RVO3(R=La, Nd) perovskites for efficient solar energy conversion materials

For the first time, density functional theory-based first-principles calculations are used to study oxide perovskites RVO3(R=La,Nd) under pressure. Structural parameters match experimental and theoretical data. The d orbital significantly contributes to the density of states (DOS) near EF for all phases. At 0 GPa, the La, V, and O PDOS at EF are ∼0.27, ∼2.18, and ∼0.44 states/eV/f.u. With increasing pressure, reflectivity and absorption spectra shift to higher energy regions. Reflectivity is nearly flat and significant for both compounds between ∼4 eV and ∼12 eV of photon energy, showing that RVO3(R=La,Nd) can be used as a UV radiation reflector. Pressure stiffens RVO3(R=La,Nd) as elastic moduli increase. Pugh's ratio, Poisson's ratio, and Cauchy's pressure show that both compounds are ductile under pressure. With laser irradiation, both materials could be ultrahigh-density optical data storage devices due to their refractive index.

Robust half-metallicity and tunable ferromagnetism in two-dimensional VClI2

Recent theoretical and experimental discoveries of two-dimensional (2D) ferromagnetic (FM) materials have sparked intense interest for their potential applications in spintronics. 2D FM materials with high spin polarization are extremely desirable for future low-dimensional spintronics. Half-metallicity plays a key role in the development of such devices. Here, we reported a new 2D nanomagnet VClI2 using the first-principles based density functional theory calculations. VClI2 shows an exciting half-metallic character with a wide half-metallic gap of 0.4 eV. The ground state favors ferromagnetic coupling with a Curie temperature Tc of 21 K. The half-metallicity with a FM ground state is further achieved by the application of an external strain and by the combined effects of the strain and the electric field. A phase transition from a half-metallic → semiconductor → metal was further observed under different stimuli with an antiferromagnetic ground state. At Ez=7.5 V/nm and in the presence of η=5% strain, the calculated Tc is estimated at 35 K, which shows a 67% increment than the Tc observed in the unstrained condition. The fascinating and unique properties suggest that VClI2 is a promising two-dimensional ferromagnetic half-metal, which can be useful for applications in future memory devices to enrich the 2D magnetic materials library.

A novel lithium decorated N-doped 4,6,8-biphenylene for reversible hydrogen storage: Insights from density functional theory

Two-dimensional (2D) carbon-based (C-based) and carbon-nitrogen (C–N) materials have great potential in the energy harvest and storage fields. We investigate a novel carbon biphenylene (C468) consisting of four-, six- and eight-membered rings of sp2 carbon atoms (Fan et al., Science, 372:852-6 (2021)) for hydrogen storage. Using first-principles based Density functional theory calculations, we study the geometrical and electronic properties of C468 and N-doped C468. Lithium (Li) atoms were symmetrically adsorbed on both sides of the substrate, and their adsorption positions were determined. The maximum gravimetric density of hydrogen (H2) adsorbed symmetrically on both sides of Li atom was studied within the scope of physical adsorption process (−0.2 eV/H2 ∼ −0.6 eV/H2). Li-decorated C468 can adsorb 8 upper hydrogen molecules and 8 lower hydrogen molecules, and Li-decorated N-doped C468 can adsorb 9 upper hydrogen molecules and 9 lower hydrogen molecules. The gravimetric densities of Li-decorated C468 and Li-decorated N-doped C468 can reach 9.581 wt% and 10.588 wt%, respectively. Our findings suggest significant insights for using Li-decorated C468 and Li-decorated N-doped C468 as hydrogen storage candidates and effectively expand the application scope of C-based materials and C–N materials.

Defects and doping engineered two-dimensional o-B2N2 for hydrogen evolution reaction catalyst: Insights from DFT simulation

In this work, a detailed investigation of the structural and electronic properties and hydrogen evolution reaction (HER) activity of the pristine, vacancy and carbon (C) doped o-B2N2 monolayer is carried out using first-principles based density functional theory. The creation of vacancy and C doping modulates structural and electronic properties of the monolayers and enhances the HER activity of o-B2N2. The BN vacancy defect, C doping at B and N sites in the monolayer enhances the magnitude of HER activity by 77.34%, 86.71% and 83.59% as compared to pristine monolayer. The modulation in the HER activity of the o-B2N2 is due to the redistribution of charge after induction of vacancy and dopant. Our results suggest that the C doping makes o-B2N2 metallic which can be utilized as an “electrocatalyst” whereas BN vacancy defected o-B2N2 monolayer is semiconducting with a band gap of ∼1 eV and can be used as “photocatalyst” for HER activity.

Two-dimensional Janus monolayers with tunable electronic and magnetic properties

In the post graphene era, the discovery of magnetism in two-dimensional (2D) intrinsic nanomagnets has opened up exciting possibilities for low-dimensional spintronics. In this article, we have reported three new 2D Janus nanomagnets VBrCl2, VBrI2, and VClBrI for the first time. First-principles based density functional theory calculations reveal that these monolayers are intrinsically magnetic with indirect band gap semiconducting properties and further the magnetic and electronic properties of these monolayers are enhanced with the application of biaxial strain and electric field. We observe interesting electronic and magnetic phase transitions, tunable band gap, and supreme enhancement of the Curie temperature (~ 686%). Large magnetic anisotropic energy (MAE) with high magnetic moment and tunable band gap property make these Janus materials useful candidates for future information storage, optoelectronics, and 2D spin circuit development.

Adsorption of imidazolium-based ionic liquids on the Fe(1 0 0) surface for corrosion inhibition: Physisorption or chemisorption?

The use of imidazolium-based ionic liquids (ILs) as corrosion inhibitors for iron was studied using both first-principles based density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD), to understand their adsorption structure, stability, and mechanism. A total of 36 ionic liquids (ILs) were selected, with various anion type (Cl−, Br−, I−, N(CN)2−, BF4− and PF6−) and alkyl chain length (Cn, n = 0, 1, 2, 4 and 6). Our calculations revealed that the ILs exhibit strong adsorption on the metal surface and is classified as chemisorption under various different criteria. AIMD simulations including explicit solvation effects verified that these adsorption configurations calculated under vacuum are representative of the adsorption process in an aqueous environment. Furthermore, we showed that the basis of this chemisorption interaction is through net electron donation from the iron slab to the imidazolium ring. Employing dispersion corrected DFT methods (DFT-D3), we demonstrated that the alkyl chain length of the cation greatly influences adsorption energy. Finally, we showed that DFT calculations model the adsorption process much more accurately compared to classical molecular dynamics calculations. The results from this computational study agree with past experimental findings and demonstrate that DFT calculations can be used to provide insight into the nature of the adsorption process of the green and sustainable ILs involved in corrosion inhibition.

Pressure-driven tunable properties of the small-gap chalcopyrite topological quantum material ZnGeSb2 : A first-principles study

Search for new topological quantum materials is the demand of time and the theoretical prediction plays a crucial role besides the obvious experimental verification. Divination of topological properties in already well-known narrow gap semiconductors is a flourishing area in quantum material. In this view we revisited the semiconductor compound in the chalcopyrite series, with a very small gap near the Fermi energy. Using the density functional theory-based first-principles calculations, we report a strong topologically nontrivial phase in chalcopyrite ${\mathrm{ZnGeSb}}_{2}$, which can act as a model system of strained HgTe. The calculations reveal the nonzero topological invariant (${Z}_{2}$), the presence of Dirac cone crossing in the surface spectral functions with spin-momentum locked spin texture. We also study the interplay between the structural parameters and electronic properties, and report the tunable topological properties due to a very small band gap, from nontrivial to trivial phase under the application of moderate hydrostatic pressure within $\ensuremath{\approx}7$ GPa. A small modification of a lattice parameter is enough to achieve this topological phase transition which is easily accomplished in an experimental laboratory. The calculations show that a discontinuity in the tetragonal distortion of noncentrosymmetric ${\mathrm{ZnGeSb}}_{2}$ plays a crucial role in driving this topological phase transition. Our results are further collaborated with a low energy $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ model Hamiltonian to validate our $\mathit{ab}\mathit{initio}$ findings. We showed that the evaluation of the model band energy dispersion under the hydrostatic pressure is consistent with the obtained results.

Electronic, elastic and thermodynamic properties of LaMgRe4 (Re= Co, Ni, Cu): A first-principles study

The magnesium-based alloys are excellent hydrogen storage materials due to outstanding physical and chemical properties. In recent years, ternary magnesium-based alloys have attracted extensive attention of scientists and researchers. In this work, the electronic, elastic and thermodynamic properties of the ternary metallic compounds LaMgRe4 (Re = Co, Ni, Cu) have been investigated in detail utilizing first-principles based density functional theory (DFT). The calculated results of formation enthalpy (ΔH) of LaMgCo4, LaMgNi4 and LaMgCu4 are −0.0641eV/atom, −0.3064 eV/atom and −0.1416eV/atom respectively, indicating that these three alloys can exist stably. The elastic constants (Cij) and phonon dispersion curves show that the three alloys conform to the mechanical and dynamic stability. In addition, the elastic modulus of polycrystals is obtained from the elastic constants of single crystals. The results of bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (ν), B/G and anisotropic coefficient (A) indicate that the ternary metallic compounds LaMgRe4 are anisotropic materials with ductility and plasticity. The thermodynamic properties such as enthalpy, free energy, entropy and heat capacity of the three alloys are obtained by phonon calculations for wide temperature range from 0 K to 1000 K, and further discussed in detail. Finally, the elastic constants of random solid solution alloys of La4Mg4Ni16-xCox (x = 0.4, 0.8, 1.6), La4Mg4Ni16-xCux (x = 2, 4, 8) and the adsorption of H2O molecule on LaMgNi4 (110) surface are also investigated.

Metastable skyrmion phase stabilized in wider T–H region of β-Mn type Co7Zn7Mn6 chiral magnet

We report the evolution of magnetic phase diagram (), by accounting for the successive magnetic phase transitions in β-Mn-type Co7Zn7Mn6, a chiral magnet by an elaborate AC susceptibility magnetometry, χ(T, H). The phase diagram of polycrystalline Co7Zn7Mn6 helimagnet reveals two distinct equilibrium skyrmion phases driven by fluctuations; conventional skyrmion phase (SkX) with helical ordering just below ∼ 215 K and disordered skyrmion phase (DSkX) just above spin-glass region. The topological nature of SkX is due to high () spins moment and magnetic disorder driven weak pinning effect manifesting into the stabilization of robust meta-stable skyrmion phase (MSkX) by trivial field-cooling via SkX at = 110 K and 150 K. We performed first-principles based density functional theory based calculations, which corroborate with the experimental structural and magnetic ground state of skyrmion-host Co7Zn7Mn6 chiral magnet.

Potential anodic application of 2D h-AlC for Li and Na-ions batteries

Choosing a suitable anode material is a fundamental step in developing the batteries to gain excellent performance. In the present work, applicability of the h-AlC monolayer is studied for anode material using first-principles based density functional theory (DFT). The metallic behaviour of the h-AlC monolayer is maintained throughout with different adsorption concentrations of Li/Na atoms, which is an excellent feature for the battery application. We report a theoretical storage capacity of 739.61 mAhg−1 and 397.58 mAhg−1 for Li and Na-adsorbed h-AlC monolayer, significantly higher than graphite, TiO2, h-AlN and many other 2D materials. A reliable diffusion barrier of 0.78 eV and 0.41 eV for Li and Na-ions on the h-AlC monolayer suggests good diffusivity. The value of open-circuit voltage (OCV) is moderate and lower than conventional anode materials such as TiO2. Our results indicate that h-AlC monolayer can be a good host material for Li-ions batteries (LIBs) and Na-ions batteries (NIBs) application. Hence, the current investigation on the potential anodic application of h-AlC monolayer is fruitful for future experimental works on lithium and sodium storage mechanisms for LIBs and NIBs.

Multiscale study to investigate nanoparticle agglomeration effect on electrical conductivity of nano-SiC reinforced polypropylene matrix composites

The clustering effect of β-SiC nanoparticles on the electrical conductivity of polypropylene matrix composites was investigated through a new multiscale modeling framework where density functional theory-based first-principles calculation and electron hopping-based numerical homogenization are integrated. According to parametric studies for particle dispersion states, the electrical conductivity of the nanocomposites clearly depends on the dispersion/agglomeration of the nanoparticles. Due to the work function of β-SiC, agglomerated particles made a greater contribution to improving electrical conductivity when compared to well-dispersed particles. In addition, the microstructure-conductivity relationship was determined using the clustering density. The proposed framework was validated with the reported experimental literature.

Theoretical design of two-dimensional visible light-driven photocatalysts for overall water splitting

Hydrogen production from water via photocatalytic water splitting has attracted great interest due to the increasing challenge from energy and environment. The light harvest, electron–hole separation, and catalytic activity are keys to enhance the efficiency of solar energy utilization, which stimulates the development of high-performance photocatalysts. In recent years, two-dimensional (2D) materials have attracted much attention due to their extremely large specific surface area, shortened carrier migration path, and excellent optical properties, but it is still a challenge to realize overall water splitting under visible light with 2D material photocatalysts experimentally. Density functional theory-based first-principles calculations provide a quicker and lower cost approach in material design than experimental exploration. In this review, recent advances in design of 2D material photocatalysts, including metal-containing, metal-free, and heterojunction materials, for photocatalytic water splitting are presented from a theoretical perspective. Future opportunities and challenges in theoretical design of 2D material photocatalysts toward overall water splitting are also included.

First-principles study of the electronic and optical properties of homo-doped 2D-hBN monolayer

The two-dimensional (2D) hexagonal boron nitride (h-BN) semiconductor has a wide bandgap and is made up of boron (B) and nitrogen (N) atoms arranged in a honeycomb lattice and connected by strong covalent bonds. We use first-principles based density functional theory (DFT), hybrid functional (GauPBE), and random phase approximation to explore the electronic and optical properties of pristine and 2D-(h-BN)1-xCx, x = 11 % and 22 % (carbon homo-doped 2D h-BN) monolayers. The formation energy analysis showed that the structural stability of carbon homo-doped 2D h-BN monolayer was better than 2D-(h-BN)1-xSx, x = 11 % and 22 % (sulfur homo-doped 2D h-BN) monolayer. The estimated band gaps in the carbon homo-doped 2D h-BN system were 5.9 (pristine), 4.25 (x = 11 % C), and 2.42 (x = 0.22 % C) eV, with the band gap decreasing as the concentration of the C atom increased. The polarization was parallel to the sheet as the carbon-homo doping concentration increased, and the band edge dropped to a minimal energy level, as validated by DFT + RPA calculations. Furthermore, the presence of LFE influence the optical properties of the homo-doped 2D h-BN.

Structural, mechanical, thermodynamic, electronic and optical characteristics of LaPtBi half-Heusler compound from first principles analyses

The first-principles based density functional theory was used to investigate the structural, mechanical, thermodynamic, electronic and optical characteristics of LaPtBi half-Heusler. The calculated crystal parameters showed good agreement with available theoretical and experimental data. Electronic band structure and density of states confirmed semimetallic behavior of the compound under study. The elastic and mechanical properties have been investigated in detail for the first time. Single crystal elastic constants satisfy Born criteria which confirms mechanical stability of LaPtBi. The optical characteristics including absorption, dielectric function, loss function, reflectivity, conductivity and refractive index were analyzed and discussed broadly, first-ever.