Utilizing First-principles Calculations Research Articles

Influence of Li Content on the Topological Inhibition of Oxygen Loss in Li-Rich Cathode Materials.

Lithium-rich layer oxide cathodes are promising energy storage materials due to their high energy densities. However, the oxygen loss during cycling limits their practical applications. Here, the essential role of Li content on the topological inhibition of oxygen loss in lithium-rich cathode materials and the relationship between the migration network of oxygen ions and the transition metal (TM) component are revealed. Utilizing first-principles calculations in combination with percolation theory and Monte Carlo simulations, it is found that TM ions can effectively encage the oxidized oxygen species when the TM concentration in TM layer exceeds 5/6, which hinders the formation of a percolating oxygen migration network. This study demonstrates the significance of rational compositional design in lithium-rich cathodes for effectively suppressing irreversible oxygen release and enhancing cathode cycling performance.

First-principles calculations into electronic, and excitonic effects of CH3NH3PbX3 (X = Br, I) perovskite solar cells

The orthorhombic phases of CH3NH3PbX3 (X = Br, I) have garnered significant research interest for their potential applications in optoelectronics. This work presents our findings regarding the geometric, electronic, and optical properties of CH3NH3PbX3 utilizing first-principles calculations based on density functions theory (DFT), and many-body perturbation theory (MBPT). Our investigation reveals that CH3NH3PbX3 exhibits direct band gap semiconductors, low effective mass, and high carrier mobility. Furthermore, CH3NH3PbX3 processes interesting optical properties, including a low exciton energy binding, and low reflectivity/high absorption efficiency. Additionally, the identified bound exciton states manifest as bright states in both materials. More importantly, the intimate correlation between optical and electronic characteristics is convincingly established through the orbital hybridization concept. These features suggest that CH3NH3PbX3 materials hold promise as an active layer for perovskite-based solar cells.

Orbital-Ordering Driven Simultaneous Tunability of Magnetism and Electric Polarization in Strained Monolayer VCl3

Two-dimensional (2D) van der Waals magnetic materials have promising and versatile electronic and magnetic properties in the 2D limit, indicating a considerable potential to advance spintronic applications. Theoretical predictions thus far have not ascertained whether monolayer VCl3 is a ferromagnetic (FM) or anti-FM monolayer; this also remains to be experimentally verified. We theoretically investigate the influence of potential factors, including C 3 symmetry breaking, orbital ordering, epitaxial strain, and charge doping, on the magnetic ground state. Utilizing first-principles calculations, we predict a collinear type-III FM ground state in monolayer VCl3 with a broken C 3 symmetry, wherein only the former two of three t 2g orbitals (a 1g, eg2π and eg1π ) are occupied. The atomic layer thickness and bond angles of monolayer VCl3 undergo abrupt changes driven by an orbital ordering switch, resulting in concomitant structural and magnetic phase transitions. Introducing doping to the underlying Cl atoms of monolayer VCl3 without C 3 symmetry simultaneously induces in- and out-of-plane polarizations. This can achieve a multiferroic phase transition if combined with the discovered adjustments of magnetic ground state and polarization magnitude under strain. The establishment of an orbital-ordering driven regulatory mechanism can facilitate deeper exploration and comprehension of magnetic properties of strongly correlated systems in monolayer VCl3.

Two-dimensional carbon rich titanium carbide (TiC3) as a high-capacity anode for potassium ion battery

In recent years, two-dimensional (2D) materials, particularly MXenes such as titanium carbide, have gained significant interest for energy storage applications. This study explores the use of potassium-adsorbed TiC3 nanosheets as potential anode materials for potassium ion batteries (KIBs), utilizing first-principles calculations. The investigated electronic, mechanical, and thermal properties of TiC3 demonstrate its suitability as an anode material. The incorporation of potassium into the host material enhances electronic conductivity while maintaining a stable layered structure. Our findings reveal promising adsorption behavior of potassium in TiC3, leading to a high theoretical specific capacity of 958 mAh/g, coupled with a low energy barrier of 0.19 eV for potassium migration, which is indicative of superior electrochemical performance. Moreover, despite the high potassium content, the electrode material shows limited volume expansion of 11.3 %, suggesting good cyclability. Additionally, the equilibrium distance between potassium and TiC3, measured at 3.11 Å, exceeds that of lithium and TiC3 (2.56 Å), potentially augmenting the material’s flexibility. Consequently, TiC3 emerges as a promising candidate for KIB anode materials.

Chiral breathing-valley locking in two-dimensional kagome lattice Ta3I8

The exploration of valley-related physics is essential to the development and refinement of valleytronics. Here, a paradigm called chiral breathing-valley locking (CBVL) is proposed, in which two chiral “breathing” phases are completely locked to their valley indexes. Utilizing first-principles calculations, a two-dimensional (2D) kagome lattice with large spontaneous valley polarization (VP), namely, monolayer Ta3I8, is proposed to realize CBVL. There are two breathing phases with chiral symmetry in Ta3I8, and they can change to each other under some conditions. The valley indexes change between “−K” and “K” along the breathing of the two chiral symmetric phases, so CBVL can be obtained. Remarkably, the VP is up to 199.7 meV, so CBVL can cause the obvious switching of the anomalous valley Hall effect (AVHE). Additionally, a 2D Janus Kagome structure TaI4X4 is constructed to confirm experimentally the feasibility of electric field modulation on the CBVL. The built-in electric field and the breathing mode can mutually influence each other in TaI4X4, which provides a synergistic regulation of the AVHE. Our findings broaden the horizon for exploring AVHE materials and provide a platform for future valleytronic applications.

Insights into (Hf-Zr-Ta-Nb)C thermal protective system: Ablation behavior, morphology evolution and atomic bonding

Utilizing first-principles calculations about A-B-O binary systems (A = Zr, Hf; B = Ta, Nb) and oxyacetylene ablation tests (2.4 MW/m2, 30 s), the synergistic effects of Hf, Zr, Ta and Nb elements in (Hf-Zr-Ta-Nb)C ceramic were studied. From the aspect of experimental results, the (Hf-Zr-Ta-Nb)C ceramic exhibited the lowest average linear variation rate (−1.2 μm/s) and thinnest oxide layer (∼170 μm), only half the thickness of (Hf–Ta)C ceramic (∼330 μm). From the aspect of protective characteristic of HfO2-based oxide layer, Ta enrichment will be easier to bring about structural instability of HfO2 than Zr and Nb elements, attributed to the easily formed Hf6Ta2O17 phase with relatively low melting point. As for ZrO2-based solid solutions, the continuous enrichment of Ta and Nb will both cause structural instability, based on the increasing trend of calculated binding energies of Ta or Nb modified ZrO2, accompanied by the spontaneous formation trend of Zr6Ta2O17 and Zr6Nb2O17 low-melting-point phases.

Exploring the adsorption characteristics of toxic CO gas on pristine, defective, and transition metal-doped I-AsP monolayer

Utilizing first-principles calculations based on density functional theory, the adsorption characteristics of toxic carbon monoxide (CO) gas adsorbed on pristine, defective, and transition metal (TM) atoms (Sc, Mn, Fe, Ni, Cu, and Zn)-doped blue arsenic-phosphorene (I-AsP) are investigated to design potential sensing platforms. The pristine and defective monolayers exhibited weak CO gas sensing performance due to weak adsorption and unaltered electronic properties. In contrast, TM-doped monolayers exhibited strong interactions and enhanced the adsorption sensitivity due to their chemisorption behavior towards CO molecule. Furthermore, electronic properties obtained through the spin density of states analysis show significant changes in the adsorption of CO molecules on the doped I-AsP monolayer, influencing electrical conductivity. The significant change in the work function of system monolayers after CO adsorption confirmed that the TM-doped I-AsP monolayer is sensitive to CO gas. Therefore, the TM-doped I-AsP monolayer possesses strong sensitivity to CO gas, among which the Sc and Cu-doped monolayers emerge as promising candidates for toxic CO gas detection.

Exploring the effects of Al and Si dopants on the accident tolerant fuels of UO2 pellets for light water reactor

This study investigates the potential of Al and Si dopants to enhance the performance of UO2 pellets used in accident tolerant fuel for light water reactors. These dopants are anticipated to improve the uranium loading level, fission product retention, and thermal conductivity of UO2 pellets, while preserving their neutronic performance. Utilizing first-principles calculations, this study analyzes the kinetics of UO2-Al and UO2-Si interactions, predicting the resulting compound types, compositions, properties, and doping techniques. The calculations consider the reaction products and their thermodynamic properties. The study proposes the use of uranium aluminide, uranium silicide, or uranium aluminum silicide (e.g., UAl3, USi, U3Si2, or U3Al2Si3) to fill the UO2 grain boundaries, as opposed to Al2O3 and SiO2. This could be achieved by synthesizing uranium aluminide and uranium silicide separately, and then mixing them with UO2.

Anchoring and catalytic insights into bilayer C4N3 material for lithium-selenium batteries: a first-principles study.

In the present work, a theoretical design for the viability of bilayer C4N3 (bi-C4N3) as a promising host material for Li-Se battery was conducted utilizing first-principles calculations. The AA- and AB-stacking configurations of bilayer C4N3 can effectively inhibit the shuttling of high-order polyselenides through the synergistic effect of physical confinement and strong Li-N bonds. Compared to conventional electrolytes, the AA- and AB-stacking bilayer C4N3 demonstrate enhanced adsorption capabilities for the polyselenides. The anchored structures of Se8 or Li2Sen (n = 1, 2, 4, 6, 8) molecules within the bilayer C4N3 exhibit high electrical conductivities, which are beneficial for enhancing the electrochemical performance. The catalytic effects of AA- and AB-stacking bilayer C4N3 were investigated by the reduction of Se8 and the energy barrier associated with the decomposition of Li2Se. The AA- and AB-stacking bilayer C4N3 can significantly decrease the activation barrier and promote the decomposition of Li2Se. The mean square displacement (MSD) curves reveal the pronounceably sluggish Li-ions diffusions in polyselenides within the AA- and AB-stacking bilayer C4N3, which in turn demonstrates the notable prospects in mitigating the shuttle effect.

Tailoring the electronic, mechanical, and carrier transport properties of 1T‐SnS2 monolayer via strain engineering: A first-principles study

Two-dimensional metal dichalcogenides have garnered significant interest in the realm of electronic applications on account of their tunable electronic structures and high carrier mobility. Utilizing first-principles calculations and deformation potential (DP) theory, a comprehensive investigation on the electronic, mechanical, and carrier transport properties of 1T-SnS2 monolayer under strain engineering is investigated in this work. The 1T-SnS2 monolayer emerges as energetically stable within an applied equal-biaxial strain interval of −8% to 8%, satisfying Born’s criterion for the elastic constants and thus manifesting remarkable mechanical stability. The lattice parameter, bond length, bond angle, and bandgap dynamically respond to the applied equal-biaxial strain. The band structure calculated using generalized gradient approximation (GGA) and spin-orbit coupling (SOC) of the 1 T-SnS2 monolayer demonstrates the characteristic of an indirect bandgap semiconductor, accompanied by tunable bandgap under strain engineering. Additionally, the carrier transport properties of 1T-SnS2 monolayer under strain engineering are also evaluated on the basis of DP theory, and a pronounced anisotropy is discovered in the effective mass, carrier relaxation time, and carrier mobility along the x- and y-direction. Notably, the application of a strain of −4% and 4% on the 1T-SnS2 monolayer has resulted in high electron mobility of 6233.21 cm2/V·s and hole mobility of 1195.62 cm2/V·s. Our present work not only underscores the substantial influence of strain engineering on the electronic, mechanical, and carrier transport properties of 1 T-SnS2 monolayer but also provides critical insights into the strain-based tuning of two-dimensional metal dichalcogenides for electronics and optoelectronics.

Unexplored single-layer CdIn2S4: Suitable electronic property and ultrahigh carrier mobility in a wide range of biaxial strains

Two-dimensional semiconductors simultaneously having suitable electronic properties and high carrier motilities are highly required in next-generation photoelectronic devices. Herein, we propose a new single-layer semiconductor, CdIn2S4, and investigate its photoelectronic properties utilizing first-principles calculations. Interestingly, we find that single-layer CdIn2S4 holds a quasi-direct moderate bandgap of 1.73 eV. Its valence band maximum and conduction band minimum are located at different atomic regions, which hinders the recombination of generated electrons and holes. Hence, single-layer CdIn2S4 has a suitable electronic structure for optoelectronics. The suitable electronic property also exists under the biaxial strains of −4%, −2%, 2 %, and 4 %, while the electron mobility ranges from ∼3000 to ∼11,000 cm2·V−1·s−1, revealing its potential application in high-speed electronics. In addition, its strong visible absorption and much-reduced exciton binding energy render abundant photogenerated electrons and holes. Summarily, the suitable electronic property, ultrahigh carrier mobility, and abundant visible absorption demonstrate that single-layer CdIn2S4 is a hopeful candidate for high-speed optoelectronics.

Magnetoelastic and Magnetoelectric Coupling in Two-Dimensional Nitride MXenes: A Density Functional Theory Study.

Two-dimensional multiferroic (2D) materials have garnered significant attention due to their potential in high-density, low-power multistate storage and spintronics applications. MXenes, a class of 2D transition metal carbides and nitrides, were first discovered in 2011, and have become the focus of research in various disciplines. Our study, utilizing first-principles calculations, examines the lattice structures, and electronic and magnetic properties of nitride MXenes with intrinsic band gaps, including V2NF2, V2NO2, Cr2NF2, Mo2NO2, Mo2NF2, and Mn2NO2. These nitride MXenes exhibit orbital ordering, and in some cases the orbital ordering induces magnetoelastic coupling or magnetoelectric coupling. Most notably, Cr2NF2 is a ferroelastic material with a spiral magnetic ordered phase, and the spiral magnetization propagation vector is coupled with the direction of ferroelastic strain. The ferroelectric phase can exist as an excited state in V2NO2, Cr2NF2, and Mo2NF2, with their magnetic order being coupled with polar displacements through orbital ordering. Our results also suggest that similar magnetoelectric coupling effects persist in the Janus MXenes V8N4O7F, Cr8N4F7O, and Mo8N4F7O. Remarkably, different phases of Mo8N4F7O, characterized by orbital ordering rearrangements, can be switched by applying external strain or an external electric field. Overall, our theoretical findings suggest that nitride MXenes hold promise as 2D multiferroic materials.

Molecular modeling for sensing of cisplatin drug by graphdiyne: electronic study via DFT.

By utilizing first-principles calculations, we studied the electronic properties of graphdiyne nanosheet (GDY) and its Si-doped counterpart, Si-GDY. Both GDY and Si-GDY sheet surfaces were examined for the drug cisplatin (CP) adsorption using adsorption energy, charge transfer, and changes in electrical conductivity as indicators. Pure GDY has little affinity for CP, according to this study. Only 7.83% of the GDY surface's bandwidth energy changed after CP adsorption. CP on Si-GDY has a gaseous energy value of -18.75kcal/mol and an aqueous energy value of - 49.39kcal/mol. The prescribed medications' water-phase solubility is determined by their solvation energy value. These charges are transferred between CP and the Si-GDY sheet, which is extremely positively charged, and this gives CP the necessary binding energy. After CP adsorption, electrical conductivity of Si-GDY increased by approximately 19.01%.

Phase transition enhanced thermoelectric performance for perovskites: The case of AgTaO3

In general, perovskite materials, such as AgTaO3, can exhibit complex structural phase transitions when the temperature changes. Different phase structures may show distinct thermoelectric properties. However, the effects of phase transition on the thermoelectric performance of AgTaO3 have yet to be systematically investigated. Thus, in this work, the electronic structures and thermoelectric properties of the p-type AgTaO3 in various phase structures are investigated by utilizing first-principles calculations and semi-classical Boltzmann transport theory. The results show that the p-type AgTaO3 in the cubic phase shows a superior power factor because the cubic phase possesses a large Seebeck coefficient and intermediate electrical conductivity. The calculated thermoelectric performance is consistent with the predictions and explanations from the analyses of the electronic structures. When the p-type AgTaO3 is transformed from the tetragonal phase to the cubic phase, its power factor is tripled, suggesting that a suitable phase transition can improve the thermoelectric properties of perovskites.

Functionalized two-dimensional iron boride compounds as novel electrode materials in Li-ion batteries.

MBenes, a class of two-dimensional metal borides, have emerged as a cutting-edge research frontier and a hotspot for electrode materials in ion batteries. This work presents a systematic investigation of the performance of two-dimensional iron boride (FeB) as an electrode material for lithium-ion batteries (LIBs), utilizing first-principles calculations. The results indicate that FeB exhibits remarkable structural stability and excellent conductivity, making it an extremely promising electrode material for LIBs. FeB has the capability to adsorb a monolayer of Li atoms, and exhibits a maximum theoretical capacity of 364 mA h g-1, a high average open circuit voltage (OCV) of 1.08 V, and a low diffusion barrier energy of 0.24 eV. Through the investigation of electrochemical properties of functionalized FeB, it has been discovered that surface functionalization exerts a positive impact on lithium storage. Theoretical lithium storage capacities of FeBT (T = F, O and S) are 538 mA h g-1, 555 mA h g-1 and 476 mA h g-1, respectively. However, the introduction of F and O functional groups significantly reduces diffusion barriers to 0.081 eV and 0.036 eV, respectively, while the introduction of the S functional group markedly decreases the average OCV to approximately 0.25 V. These interesting findings suggest that FeB has great potential in the future development of LIBs.

Controlling the magnetic anisotropy of RumIrn (m + n = 3) clusters using the MgO(001) substrate.

Large perpendicular magnetic anisotropy energy (MAE) and flexible regulation of the magnitude and direction of MAE have great potential for application in information storage devices. Here, utilizing first-principles calculations, we investigated the magnetic properties of free and MgO(001) supported RumIrn clusters (RumIrn@MgO(m + n = 3)). The results indicate that the MAE of mixed clusters increases with the number of Ir atoms due to Ir having a strong coupling between the non-degenerate dxy and dx2-y2 states. The MAE of free Ir3 is -8.18 meV with the easy magnetization direction parallel to the x-axis, while the MAE of supported Ir3 on the MgO substrate increases by a factor of 2.6, and the easy magnetization axis of the structure is shifted to a direction perpendicular to the substrate surface. This change in MAE is due to the significant enhancement in the coupling between the non-degenerate dyz and dx2-y2 states near the Fermi level of Ir3 atoms. Moreover, Ir3@MgO possesses high thermodynamic stability. These results give a new method for manipulating MAE and the direction of easy magnetization, which has great potential for application in magnetic nanodevices.

Investigation of superconductivity in ultrahigh pressure phases of yttrium

The superconductivity of yttrium metal under high pressure were systematically investigated by utilizing first-principles calculations. Based on the evolutionary structure searches, we have proposed a new ultrahigh pressure phase of C2/m that is energetically competitive to the previously reported Fmm2. The electron-phonon coupling calculations demonstrated a Tc of 16.97 K at 700 GPa in our proposed C2/m, whereas the Tc in Fmm2 was estimated to be 12.19–9.46 K in the pressure range of 600–800 GPa accompanied by a declining trend upon compression. Further analyses of Fermi surface nesting functions reveal that the shrinking Tc in Fmm2 is dominated by phonon frequencies and N(εF), while the difference of Tc's between C2/m and Fmm2 is mainly attributed to the tremendous difference of electron-phonon matrix element. Our findings would offer fundamental insights for understanding the superconducting mechanism in yttrium and even other rare earth superconductors under BCS framework.

Ferrate-Modified Biochar for Greenhouse Gas Mitigation: First-Principles Calculation and Paddy Field Trails

Modified biochars have attracted attention for reducing greenhouse gas emissions in paddy fields. However, material screening difficulties and lengthy effect validation periods have restricted their development. We proposed a theoretical calculation method to guide short-term field trials in this study. Utilizing first-principles calculations, we determined that sodium ferrate-modified biochar (Fe@C) would limit methane (CH4) and nitrous oxide (N2O) emissions. Field trials confirmed that Fe@C increased rice yields and active organic carbon content in soil and reduced methane emissions and the global warming potential. However, applying sodium ferrate alone significantly reduced N2O emissions. Correlation analysis showed that methane was significantly negatively correlated with yield and the soil carbon pool labile index. N2O was significantly negatively correlated with urease activity, and significantly positively correlated with the soil carbon pool management index. Therefore, Fe@C provides a high-yielding management measure that enhances soil labile organic carbon. Additionally, its effects were controlled by the proportion of sodium ferrate. Our work provides a new strategy to guide the design of paddy field experiments via theoretical calculations, greatly shortening research time and providing solutions for carbon sequestration and emissions reduction.

Achieving thermally stable nanoparticles in chemically complex alloys via controllable sluggish lattice diffusion

Nanoparticle strengthening provides a crucial basis for developing high-performance structural materials with potentially superb mechanical properties for structural applications. However, the general wisdom often fails to work well due to the poor thermal stability of nanoparticles, and the rapid coarsening of these particles will lead to the accelerated failures of these materials especially at elevated temperatures. Here, we demonstrate a strategy to achieve ultra-stable nanoparticles at 800~1000 °C in a Ni59.9-xCoxFe13Cr15Al6Ti6B0.1 (at.%) chemically complex alloy, resulting from the controllable sluggish lattice diffusion (SLD) effect. Our diffusion kinetic simulations reveal that the Co element leads to a significant reduction in the interdiffusion coefficients of all the main elements, especially for the Al element, with a maximum of up to 5 orders of magnitude. Utilizing first-principles calculations, we further unveil the incompressibility of Al induced by the increased concentration of Co plays a critical role in controlling the SLD effect. These findings are useful for providing advances in the design of novel structural alloys with extraordinary property-microstructure stability combinations for structural applications.

Strain-promoted conductive metal-benzenhexathiolate frameworks for overall water splitting

Designing efficient catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a desirable strategy for overall water splitting and the generation of clean and renewable energies. Herein, the electrocatalytic HER and OER activity of the conductive metal-benzenhexathiolate (M-BHT) frameworks has been evaluated utilizing first-principles calculations. The in-plane π-d conjugation of M-BHT guarantees fast electron transfer during electrocatalytic reactions. Notably, Rh-BHT holds the promise of bifunctional HER/OER activity with the overpotentials of 0.07/0.36 V. Furthermore, the application of strain engineering tailors the adsorption of intermediates and promotes the overall water splitting performance. Rh-BHT with the +1% tensile strain shows the HER/OER overpotential of 0.02/0.37 V. This work not only demonstrates the prospects of conductive metal-organic frameworks in electrocatalysis but also offers new insights into designing efficient catalysts by strain engineering.