Population analysis of plane-wave electronic structure calculations of bulk materials

A systematic DFT study of structure and electronic properties of titanium dioxide

DFT functionals are of paramount importance for an accurate electronic and structural description of transition metal systems. In this work, a systematic analysis using some well-known and commonly used DFT functionals is performed. A comparison of the structural and energetic parameters calculated with the available experimental data is made in order to find the adequate functional for an accurate description of the TiO2 bulk and surface of both anatase and rutile structures. In the absence of experimental data on the surface energy, the theoretical predictions obtained using the high-accuracy HSE06 functional were used as a reference to compare against the surface energy values calculated with the other DFT functionals. A clear improvement in the electronic description of both anatase and rutile was observed by introducing the Hubbard U correction term to PBE, PW91, and OptPBE functionals. The OptPBE-U4 functional was found to offer a good compromise between accurately describing the structural and electronic properties of titania.

First principles study on the structural stability, mechanical stability and optoelectronic properties of alkali-based single halide perovskite compounds XMgI3 (X = Li/Na): DFT insight

Metal-halide perovskites are recognized as cutting-edge solar energy technology, boasting remarkable absorption capabilities, minimal environmental impact, and cost-effectiveness. This study delves into the structural stability, mechanical stability, and optoelectronic properties of lead-free halide perovskites, specifically XMgI3 (X = Li/Na), by utilizing the CASTEP and WIEN2k software along with the GGA-PBE and Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange-correlation functions to compare their electronic properties. The structural and mechanical stabilities were confirmed by assessing their tolerance factor and formation energy and by evaluating their elastic constants, respectively. Using the TB-mBJ exchange-correlation potential function, the calculated indirect band gap values for LiMgI3 and NaMgI3 were 2.474 and 2.556 eV, respectively. These band gaps are suitable for solar energy harvesting due to their broad optical absorption ranging from infrared to visible light. The partial density of states and the total density of states were determined to investigate the contribution of individual atoms. Consequently, this study can guide researchers focusing on the experimental synthesis of these materials at the laboratory scale for in-depth exploration, particularly in applications such as photovoltaics and various optoelectronic devices.

Embedded Hybrid-Dimensional Heterointerface for Filament Modulation in 2D Material-Based Artificial Nociceptor

Nociceptors are key sensory receptors that transmit warning signals to the central nervous system in response to painful stimuli. This fundamental process is emulated in an electronic device by developing a novel artificial nociceptor with an ultrathin, nonstoichiometric gallium oxide (GaOx)-silicon oxide heterostructure. A large-area 2D-GaOx film is printed on a substrate through liquid metal printing to facilitate the production of conductive filaments. This nociceptive structure exhibits a unique short-term temporal response following stimulation, enabling a facile demonstration of threshold-switching physics. The developed heterointerface 2D-GaOx film enables the fabrication of fast-switching, low-energy, and compliance-free 2D-GaOx nociceptors, as confirmed through experiments. The accumulation and extrusion of Ag in the oxide matrix are significant for inducing plastic changes in artificial biological sensors. High-resolution transmission electron microscopy and electron energy loss spectroscopy demonstrate that Ag clusters in the material dispersed under electrical bias and regrouped spontaneously when the bias is removed owing to interfacial energy minimization. Moreover, 2D nociceptors are stable; thus, heterointerface engineering can enable effective control of charge transfer in 2D heterostructural devices. Furthermore, the diffusive 2D-GaOx device and its Ag dynamics enable the direct emulation of biological nociceptors, marking an advancement in the hardware implementation of artificial human sensory systems.

First-principles study on structural stabilities, mechanical properties, and biaxial strain-induced superconductivity in Janus MoWC monolayer

The unique attributes of hydrophilicity, expansive surface groups, remarkable flexibility, and superior conductivity converge in MXene, a pioneering 2D material. Owing to MXene's exceptional properties, diverse strategies have been explored to enhance its characteristics. Janus MXene and stress-strain response considerations represent the primary avenues of interest today. In this study, we investigated the Janus MXene structure under biaxial stress using first-principles calculations. The most stable configuration of Janus MoWC MXene identified in our analysis exhibits an atomic arrangement known as the hexagonal (2H) phase. Subsequently, we examined the mechanical and electronic properties of 2H-MoWC when subjected to biaxial strain. Our findings indicate that the 2H phase of Janus MoWC MXene demonstrates superior strength compared to the tetragonal (1T) phase. Analysis of the ELF of the 2H-MoWC structure unveiled that the robust C-C bond within the material is the underlying factor enabling the 2H phase to withstand a maximum of 9% tensile strain. Furthermore, we demonstrate that 2H-MoWC is a superconductor with the superconducting temperature (Tc) of 1.6 K, and the superconductivity of 2H phase can be enhanced by biaxial strain with the Tc reaching 7 K. This study offers comprehensive insights into the properties of Janus MoWC monolayer under biaxial stress, positioning it as a promising candidate for 2D straintronic applications.

First principles insight into the study of the structural, stability, and optoelectronic properties of alkali-based single halide perovskite ZSnCl3 (Z = Na/K) materials for photovoltaic applications

Metal halide perovskites are crystalline materials with a sharp increase in popularity and rapidly becoming a major contender for optoelectronic device applications. In this work, we provide the optoelectronic features of a possible novel candidate, ZSnCl3 (Z = Na/K) Sn-based on a detailed numerical simulation. The output of the current computations is compared to the results that are currently available, and a respectable agreement is noted. The studied compounds were cubic in nature and structurally stabe. The mechanical properties reflect the mechanical stability and ductility of the proposed materials. The Sn-based single perovskite compounds proposed in this study are mechanically stable and ductile. The narrow direct band gap for NaSnCl3 and KSnCl3 are 1.36 eV and 1.47 eV, respectively, using the HSE06 hybrid function with the Boltztrp2 integrated in Quantum ESPRESSO (QE) software. The effective use of these compounds in perovskite solar cells and other optoelectronic applications was confirmed by optical absorption spectral measurements conducted in the photon energy range of 0-20 eV.

Incorporation of Ag in Co9S8-Ni3S2 for Predominantly Enhanced Electrocatalytic Activities for Oxygen Evolution Reaction: A Combined Experimental and DFT Study

Electrodeposition of abundant metals to fabricate efficient and durable electrodes indicate a viable role in advancing renewable electrochemical energy tools. Herein, we deposit Co9S8-Ag-Ni3S2@NF on nickel foam (NF) to produce Co9S8-Ag-Ni3S2@NF as a exceedingly proficient electrode for oxygen evolution reaction (OER). The electrochemical investigation verifies that the Co9S8-Ag-Ni3S2@NF electrode reveals better electrocatalytic activity to OER because of its nanoflowers' open-pore morphology, reduced overpotential (η10=125 mV), smaller charge transfer resistance, long-term stability, and a synergistic effect between various components, which allows the reactants to be more easily absorbed and subsequently converted into gaseous products during the water electrolysis route. Density functional theory (DFT) calculation as well reveals the introduction of Ag (222) surface into the Co9S8 (440)-Ni3S2 (120) structure increases the electronic density of states (DOS) per unit cell of a system and increases the electrocatalytic activity of OER by considerably lowering the energy barriers of its intermediates. This study provides the innovation of employing trimetallic nanomaterials immobilized on a conductive, continuous porous three-dimensional network formed on a nickel foam (NF) substrate as a highly proficient catalyst for OER.

Site preference and local structural stability of Bi(III) substitution in hydroxyapatite using first-principles simulations

Bismuth (Bi(III)) substitution in hydroxyapatite (HAp) lattice confers unique properties such as antibacterial, catalytic, radiosensitization, and conductive properties while preserving the innate bioactivity. Understanding the local structural changes upon Bi3+ substitution is essential for controlling the stability and optimizing the properties of HAp. Despite numerous experimental studies, the precise substitution behaviors, such as site preference and structural stability, remain incompletely understood. In this study, the substitution behavior of Bi(III) into the HAp lattice with formula of Ca9Bi(PO4)6(O)(OH) was investigated via first-principles simulation by implementing density functional theory. Energy calculations showed that Bi3+ preferentially occupies the Ca(2) site with an energy difference of ∼0.02 eV per atom. Local structure analysis revealed higher bond population values and an oxygen coordination shift from 7 to 6 for the Ca(2) site, attributed to the greater covalent interactions and its flexible environment accommodating the bulky Bi3+ ion and its stereochemically active lone pair. This work provides the first comprehensive investigation on Bi3+ ion substitution site preference in HAp using first-principles simulations.

First-principles study of multifunctional Mn2B3 materials with high hardness and ferromagnetism

Transition metal boride TM2B3 is widely studied in the field of physics and materials science. However, Mn2B3 has not been found in Mn-B systems so far. Mn2B3 undergoes phase transitions from Cmcm (0-28 GPa) to C2/m (28-80 GPa) and finally to C2/c (80-200 GPa) under pressure. Among these stable phases, Cmcm- and C2/m-Mn2B3s comprise six-membered boron rings and C2/c-Mn2B3 has wavy boron chains. They all have good mechanical properties and can become potential multifunctional materials. The strong B-B covalent bonding is mainly responsible for the structural stability and hardness. Comparison of the hardness of the five TM2B3s with different bonding strengths of TM-B and B-B bonds reveals a nonlinear change in the hardness. According to the Stoner model, these structures possess ferromagnetism, and the corresponding magnetic moments are almost the same as those of GGA and GGA + U (U = 3.9 eV, J = 1 eV).

Effect of PAM on Surface Hydrophobicity of Montmorillonite and Difference of Interface Adsorption: An Experimental and Simulation Study

How to realize efficient treatment of coal slime generated by a coal washing operation is an urgent problem to be solved in this industry. The presence of clay minerals, especially highly hydrophilic montmorillonite (MMT), is the key to the poor treatment effect of coal slime. Polyacrylamide (PAM) is very popular as a polymer agent to improve the treatment of coal slime. However, when it is used to treat coal slime with a high content of MMT, the selection of PAM type and the mechanism of action are still lacking. In this study, the effects of different types of PAM on the treatment of coal slime water containing MMT are considered by sedimentation and press filtration tests. The interaction mechanism of PAM on the MMT surface is studied by using ζ-potential, Brunauer-Emmett-Teller (BET) analysis, low-field nuclear magnetic resonance, density functional theory (DFT), and molecular dynamics (MD) simulations. The results show that the three PAM can improve the sedimentation and filtration effect of coal slime water, and the performance is CPAM > NPAM > APAM. The ζ-potential of the MMT (001) surface increases under the action of three PAM, and the effect of CPAM is the most significant. The adsorption of PAM on the MMT (001) surface has the ability to neutralize the surface charge of MMT. The flocculation of MMT particles under PAM results in an increase of particle size and a decrease of specific surface area. Meanwhile, the pore volume of MMT decreases, and the average pore size increases. In addition, PAM mainly removes vicinal water on the MMT surface. The active sites of the MMT surface and PAM are calculated by DFT. The adsorption of three PAM structural units on the MMT Na-001 surface and non-001 surface is nonbonding interaction, and the adsorption energy of CPAM is the largest. And the left shift of εp of the O atom on the MMT surface is conducive to the stable adsorption of CPAM. The MD results show that the concentration of water molecules on the surface of MMT Na-001 decreases after PAM is adsorbed on the MMT Na-001 surface, indicating that PAM can keep water molecules away from the surface of MMT, which means that the hydrophobicity of the MMT surface is enhanced. This study has guiding significance for the selection of PAM and the development of new flocculants in the treatment of coal slime with a high content of MMT.

Prediction study of structural, electronic and optical properties of 4C16H10Br2O2 Bis (m-bromobenzoyl) methane crystals

By first-principles calculations with density functional theory and a pseudopotential approach, the structural, electronic, and optical properties of the anhydrous 4C16H10Br2O2 Bis (2-Bromobenzoyl) Methane crystals in Pbnc (N°60) and P21/c (N°14) space group are investigated. All computations are determined by a generalized gradient approximation, local density approximation and an ultra-soft pseudopotential. The calculated equilibrium parameters are in good agreement with their available experimental data. This calculation shows that the GGA/PW91 functional overestimate the lattice constant, unlike the LDA/CA-PZ. The Br-C bond distance of 1.856 (1.902) Å is comparable with experimental value of 1.901 (1.896) Å in Pbnc (P21/c) space groups. The direct band gap nature is obtained for both space groups Pbnc and P21/c, since the maximum of the valence band and the minimum of the conduction band are both situated at the YA center.

Structure and elasticity of CaC2O5 suggests carbonate contribution to the seismic anomalies of Earth's mantle

Knowledge of carbonate compounds under high pressure inside Earth is key to understanding the internal structure of the Earth, the deep carbon cycle and major geological events. Here we use first-principles simulations to calculate the structure and elasticity of CaC2O5-minerals with different symmetries under high pressure. Our calculations show that CaC2O5-minerals represent a group of low-density low-seismic-wave velocity mantle minerals. Changes in seismic wave velocity caused by the phase transformation of CaC2O5-Cc to CaC2O5-I[Formula: see text]2d (CaC2O5-C2-l) agree with wave velocity discontinuity at a depth of 660 km in the mantle transition zone. Moreover, when CaC2O5-Fdd2 transforms into CaC2O5-C2 under 70 GPa, its shear wave velocity decreases by 7.4%, and its density increases by 5.8%, which is consistent with the characteristics of large low-shear-velocity provinces (LLSVPs). Furthermore, the shear wave velocity of CaC2O5-I[Formula: see text]2d is very similar to that of cubic Ca-perovskite, which is one of the main constituents of the previously detected LLSVPs. Therefore, we propose that CaC2O5 and its high-pressure polymorphs may be a main component of LLSVPs.

Atomic Charge Dependency of Spiropyran/Merocyanine Adsorption as a Precursor to Surface Isomerization Reactions

This computational study investigates the adsorption of various spiropyran and merocyanine isomers on a NaCl substrate using a combination of density functional theory (DFT) and molecular mechanics (MM) calculations. Four different charge methods were used to determine the partial atomic charges for the adsorbate molecules, including Mulliken population analysis and three electrostatic potential (ESP) methods (Merz-Kollman, ChelpG, and Hu-Lu-Yang), while three different force fields (AMBER 3, CHARMM 27, and MM+) were employed for the MM calculations. The results show that the various DFT charge methods produced similar outcomes for the molecules' partial atomic charges, with some exceptions for individual atoms and methods. Additionally, it was found that the ESP charge methods were more sensitive to the conformer orientation than the Mulliken approach. The adsorption behavior of merocyanine conformers with the central bond in trans orientation (T-conformers) was similar for various configurations, with the molecule adsorbing mostly flat with its aromatic rings almost parallel to the substrate. However, C-conformers (with their central bond in cis orientation) and spiropyran isomers exhibited inconsistent adsorption behavior, mostly because only some of the aromatic rings contributed to the adsorption behavior. Due to additional van der Waals interactions of more aromatic rings, the adsorption energies for T-conformers are consistently 0.2-0.3 eV higher than for C-conformers and for spiropyran. The study found that the adsorption geometries and energies of stable T-conformers were independent of the partial atomic charge scheme and force field used, and C-conformers show parameter-dependent behavior upon adsorption, leading to metastable configurations. These findings indicate viable pathways during the spiropyran-merocyanine isomerization reactions. Therefore, the results provide initial insights into the possibility of switching spiropyran isomers into merocyanine isomers and vice versa after adsorption onto substrates.

Bulk Modification of Porous TiNb2 O7 Microsphere to Achieve Superior Lithium-Storage Properties at Low Temperature

TiNb2 O7 , as a promising alternative of Li4 Ti5 O12 , exhibits giant potential as low-temperature anode due to its higher theoretical capacity and comparable structural stability. However, the sluggish electronic conductivity still remains a challenge. Herein, bulk modification of Cu+ doping in porous TiNb2 O7 microsphere is proposed via a simple one-step solvothermal method with subsequent calcination treatment. The results show that the electronic conductivity is improved effectively due to the reduced band gap after doping, while enhanced lithium-ion diffusion is achieved benefiting from the increased interplanar spacing. Therefore, the optimal sample of Cu0.06 Ti0.94 Nb2 O7 exhibits a high reversible capacity of 244.4 mA h g-1 at 100 mA g-1 after 100 cycles, superior rate capability, and long-term cycling stability at 1000 mA g-1 at room temperature. Particularly, it can also display good performance in a wide temperature range from 25 to -30 °C, including a reversible capacity of 76.6 mA h g-1 at -20 °C after 200 cycles at 200 mA g-1 . Moreover, Cu0.06 Ti0.94 Nb2 O7 //LiFePO4 full cell can deliver a high reversible capacity of 177.5 mA h g-1 at 100 mA g-1 . The excellent electrochemical properties at both ambient and low-temperatures demonstrate the great potential of Cu+ -doped TiNb2 O7 in energy-storage applications.

Lead-free novel perovskite Ba3AsI3: First-principles insights into its electrical, optical, and mechanical properties

Lead-free halide perovskites are a crucial family of materials in the fabrication of solar cells. At present, Solar cells are facing several challenges such as mechanical and thermodynamic instability, toxicity, unsuitable optical parameters, bandgap, and absorption coefficient. Ba3AsI3 is a halide perovskite which has demonstrated good efficiency and tremendous promise for usage in solar cell applications, and it offers a possible solution to these issues. In this study, the properties of the Ba3AsI3 perovskite solar cell were investigated using first-principles density functional theory (FP-DFT) calculations with the CASTEP (Cambridge serial total energy package) formulation. Most of its physical qualities, including its elasticity, electrical composition, bonding, optoelectronic characteristics, and optical characteristics have not yet been explored. In this work, these unexplored properties have been thoroughly investigated using density functional theory-based computations. The Born-Huang criterion and phonon dispersion characteristics have revealed that the material is mechanically stable. The bonding nature has been investigated using the density of states curves, Mulliken population analysis, and electronic charge density. Additionally, different elastic parameters demonstrate that Ba3AsI3 has reasonably high machinability and is mechanically isotropic. ELATE's three-dimensional visualization and optical properties also show isotropic behavior in all directions. The band structure shows that the bandgap is direct. Based on its direct bandgap, stability, large range of absorption coefficient, and suitable optical parameters, Ba3AsI3 is recommended as an absorber layer for solar cell fabrication in a near future.

Theoretical Dissection of Cation-Deficient Layered Ruddlesden-Popper Oxysulfide Perovskites with a High-Efficiency Carrier Transport Channel

The search for lead-free perovskite materials has triggered intensive interest. Here, we study the electronic structures and optical properties of cation-deficient Ruddlesden-Popper oxysulfide perovskites Ln2Ti2O5S2 (Ln = Sc, Y, or La), with a tunable band gap of 1.45-2.1 eV and a small exciton binding energy of ∼0.1 eV, among which Y2Ti2O5S2 has been synthesized experimentally. Sc2Ti2O5S2 possesses the largest light absorbance in the visible region. We further rationalize the light absorption via the transition dipole moment and suggest potential applications of Sc2Ti2O5S2 in solar cells and Y2Ti2O5S2 and La2Ti2O5S2 in water splitting. In addition, this family exhibits small effective masses within the x-y plane and large ones along the z direction. Most importantly, electron gas-like carrier behaviors are observed within the Ti-O bond region, offering a diffusion channel for electron transport. These findings greatly advance our understanding of lead-free perovskites and offer a novel material platform for future optoelectronic devices.

Stability of Single Gold Atoms on Defective and Doped Diamond Surfaces

Polycrystalline boron-doped diamond (BDD) is widely used as a working electrode material in electrochemistry, and its properties, such as its stability, make it an appealing support material for nanostructures in electrocatalytic applications. Recent experiments have shown that electrodeposition can lead to the creation of stable small nanoclusters and even single gold adatoms on the BDD surfaces. We investigate the adsorption energy and kinetic stability of single gold atoms adsorbed onto an atomistic model of BDD surfaces by using density functional theory. The surface model is constructed using hybrid quantum mechanics/molecular mechanics embedding techniques and is based on an oxygen-terminated diamond (110) surface. We use the hybrid quantum mechanics/molecular mechanics method to assess the ability of different density functional approximations to predict the adsorption structure, energy, and barrier for diffusion on pristine and defective surfaces. We find that surface defects (vacancies and surface dopants) strongly anchor adatoms on vacancy sites. We further investigated the thermal stability of gold adatoms, which reveals high barriers associated with lateral diffusion away from the vacancy site. The result provides an explanation for the high stability of experimentally imaged single gold adatoms on BDD and a starting point to investigate the early stages of nucleation during metal surface deposition.

Highly efficient and stable lead-free cesium copper halide perovskites for optoelectronic applications: A DFT based study

Recently synthesized industrially significant perovskites C s 3 C u 2 X 5 (X = C l , B r , I ) are subjected to a density functional theory (DFT) investigation utilizing the CASTEP code. This study explores various physical features, including structural, optical, thermodynamic, elastic, mechanical, and electronic properties. There is a strong correlation between the optimized structure parameters and the existing experimental data, which demonstrates the reliability of our DFT-based computations. The band structure and density of states (TDOS and PDOS) analysis revealed that all the studied perovskites are direct band gap semiconductors, and C s 3 C u 2 B r 5 has the smallest band gap (2.092 eV). We also discussed the mechanical and cell stability using the Born stability criterion and formation energy, respectively. The mechanical and dynamic stability of each phase is confirmed by the analysis of the elastic constants. According to the computed values of Pugh's and Poisson's ratios as well as Cauchy's pressure, all of the studied compounds are ductile in nature. The study of density of states, total charge density, and Mulliken atomic populations reveal that all the compounds have complex bonding with both ionic and covalent properties. Finally, utilizing the elastic constant data, the Debye temperatures of C s 3 C u 2 C l 5 , C s 3 C u 2 B r 5 , and C s 3 C u 2 I 5 have been determined as 82.90 K, 100.00 K, and 80.70 K, respectively. The analysis of thermodynamics (relatively low values of both Θ D and K min ) as well as optical properties indicate that all the investigated materials have the potential to serve as thermal barrier coating (TBC) materials.

DFT investigation of the dissolution trends of NiTi alloys with the B2 and B19' phases during the initial oxidation stage

The selective corrosion of NiTi alloys was studied using density functional theory calculations, and the dissolution trends of the NiTi-B₂ and NiTi-B19' phases in the initial oxidation stage were compared to predict their corrosion difference. The dissolution process of Ni and Ti was simulated by creating Ni or Ti vacancies on the unoxidized and oxidized NiTi alloy surfaces. The results show that the surface vacancy formation energy of Ti vacancies is higher than that of Ni vacancies, indicating that Ti is more difficult to dissolve than Ni. Furthermore, oxidation promotes and impedes the dissolution of Ni and Ti, respectively. This study improves the fundamental understanding of the corrosion mechanism of NiTi alloys.

Imaging of the electronic bonding of diamond at pressures up to 2 million atmospheres

Diamond shows unprecedented hardness. Because hardness is a measure of resistance of chemical bonds in a material to external indentation, the electronic bonding nature of diamond beyond several million atmospheres is key to understanding the origin of hardness. However, probing the electronic structures of diamond at such extreme pressure has not been experimentally possible. The measurements on the inelastic x-ray scattering spectra for diamond up to 2 million atmospheres provide data on the evolution of its electronic structures under compression. The mapping of the observed electronic density of states allows us to obtain a two-dimensional image of the bonding transitions of diamond undergoing deformation. The spectral change near edge onset is minor beyond a million atmospheres, while its electronic structure displays marked pressure-induced electron delocalization. Such electronic responses indicate that diamond's external rigidity is supported by its ability to reconcile internal stress, providing insights into the origins of hardness in materials.

Nanomaterials Based on Collaboration with Multiple Partners: Zn3Nb2O8 Doped with Eu3+ and/or Amino Substituted Porphyrin Incorporated in Silica Matrices for the Discoloration of Methyl Red

Designing appropriate materials destined for the removal of dyes from waste waters represents a great challenge for achieving a sustainable society. Three partnerships were set up to obtain novel adsorbents with tailored optoelectronic properties using silica matrices, Zn₃Nb₂O₈ oxide doped with Eu³⁺, and a symmetrical amino-substituted porphyrin. The pseudo-binary oxide with the formula Zn₃Nb₂O₈ was obtained by the solid-state method. The doping of Zn₃Nb₂O₈ with Eu³⁺ ions was intended in order to amplify the optical properties of the mixed oxide that are highly influenced by the coordination environment of Eu³⁺ ions, as confirmed by density functional theory (DFT) calculations. The first proposed silica material, based solely on tetraethyl orthosilicate (TEOS) with high specific surface areas of 518-726 m²/g, offered better performance as an adsorbent than the second one, which also contained 3-aminopropyltrimethoxysilane (APTMOS). The contribution of amino-substituted porphyrin incorporated into silica matrices resides both in providing anchoring groups for the methyl red dye and in increasing the optical properties of the whole nanomaterial. Two different types of methyl red adsorption mechanisms can be reported: one based on surface absorbance and one based on the dye entering the pores of the adsorbents due to their open groove shape network.

The location of the chemical bond. Application of long covalent bond theory to the structure of silica

Oxygen is the most abundant terrestrial element and is found in a variety of materials, but still wanting is a universal theory for the stability and structural organization it confers. Herein, a computational molecular orbital analysis elucidates the structure, stability, and cooperative bonding of α-quartz silica (SiO₂). Despite geminal oxygen-oxygen distances of 2.61-2.64 Å, silica model complexes exhibit anomalously large O-O bond orders (Mulliken, Wiberg, Mayer) that increase with increasing cluster size-as the silicon-oxygen bond orders decrease. The average O-O bond order in bulk silica computes to 0.47 while that for Si-O computes to 0.64. Thereby, for each silicate tetrahedron, the six O-O bonds employ 52% (5.61 electrons) of the valence electrons, while the four Si-O bonds employ 48% (5.12 electrons), rendering the O-O bond the most abundant bond in the Earth's crust. The isodesmic deconstruction of silica clusters reveals cooperative O-O bonding with an O-O bond dissociation energy of 4.4 kcal/mol. These unorthodox, long covalent bonds are rationalized by an excess of O 2p-O 2p bonding versus anti-bonding interactions within the valence molecular orbitals of the SiO₄ unit (48 vs. 24) and the Si₆O₆ ring (90 vs. 18). Within quartz silica, oxygen 2p orbitals contort and organize to avoid molecular orbital nodes, inducing the chirality of silica and resulting in Möbius aromatic Si₆O₆ rings, the most prevalent form of aromaticity on Earth. This long covalent bond theory (LCBT) relocates one-third of Earth's valence electrons and indicates that non-canonical O-O bonds play a subtle, but crucial role in the structure and stability of Earth's most abundant material.

Facile Synthesis of Nb-Doped CoTiO3 Hexagonal Microprisms as Promising Anode Materials for Lithium-Ion Batteries

Bimetallic oxides are demonstrated to show better electrochemical performance than single transition metal oxides. Recently, ilmenite-type transition metal titanate (MTiO3, M = Fe, Co, Ni, etc.) is emerging as a promising anode for lithium-ion batteries (LIBs) due to its comparable theoretical capacity and small volumetric change during cycling. However, the practical electrochemical performance is still harmed by its poor electronic conductivity. Herein, for the first time, a Nb-doping strategy is adopted to modify CoTiO3 hexagonal microprisms by a facile solvothermal method combined with an annealing treatment. Benefiting from the unique 1D morphology and the ameliorated conductivities induced by Nb-doping, the optimized Nb-doped CoTiO3 anode exhibits an improved lithium-storage capacity of 233 mA h g−1 at 100 mA g−1 after 100 cycles and excellent rate capability, which are superior to that of pure CoTiO3. This work sheds light on the potential application of titanium containing bimetallic oxide in the next-generation advanced rechargeable LIBs.

Identification of Graphene Dispersion Agents through Molecular Fingerprints

The scalable production and dispersion of 2D materials, like graphene, is critical to enable their use in commercial applications. While liquid exfoliation is commonly used, solvents such as N-methyl-pyrrolidone (NMP) are toxic and difficult to scale up. However, the search for alternative solvents is hindered by the intimidating size of the chemical space. Here, we present a computational pipeline informing the identification of effective exfoliation agents. Classical molecular dynamics simulations provide statistical sampling of interactions, enabling the identification of key molecular descriptors for a successful solvent. The statistically representative configurations from these simulations, studied with quantum mechanical calculations, allow us to gain insights onto the chemophysical interactions at the surface-solvent interface. As an exemplar, through this pipeline we identify a potential graphene exfoliation agent 2-pyrrolidone and experimentally demonstrate it to be as effective as NMP. Our workflow can be generalized to any 2D material and solvent system, enabling the screening of a wide range of compounds and solvents to identify safer and cheaper means of producing dispersions.

A Conceptual Strategy toward High-Reliability Metal-Thermoplastic Hybrid Structures Based on a Covalent-Bonding Mechanism

Metal-thermoplastic hybrid structures have proven their effectiveness to achieve lightweight design concepts in both primary and secondary structural components of advanced aircraft. However, the drastic differences in physical and chemical properties between metal and thermoplastic make it challenging to fabricate high-reliability hybrid structures. Here, a simple and universal strategy to obtain strong hybrid structures thermoplastics is reported by regulating the bonding behavior at metal/thermoplastic interfaces. To achieve such, we first researched and uncovered the bonding mechanism at metal/thermoplastic interfaces by experimental methods and density functional theory (DFT) calculations. The results suggest that the interfacial covalency, which is formed due to the interfacial reaction between high-electronegativity elements of thermoplastics and metallic elements at metal surfaces, dominates the interfacial bonding interaction of metal-thermoplastic hybrid structures. The differences in electronegativity and atomic size between bonding atoms influence the covalent-bond strength and finally control the interfacial reliability of hybrid structures. Based on our covalent-bonding mechanism, the carboxyl functional group (COOH) is specifically grafted on polyetheretherketone (PEEK) by plasma polymerization to increase the density and strength of interfacial covalency and thus fabricate high-reliability hybrid structures between PEEK and A6061-T6 aluminum alloy. Current work provides an in-depth understanding of the bonding mechanism at metal-thermoplastics interfaces, which opens a fascinating direction toward high-reliability metal-thermoplastic hybrid structures.

Room-Temperature Superconductivity in Yb/Lu Substituted Clathrate Hexahydrides under Moderate Pressure

Room temperature superconductivity is a dream that mankind has been chasing for a century. In recent years, the synthesis of H₃S, LaH₁₀, and C-S-H compounds under high pressures has gradually made that dream become a reality. But the extreme high pressure required for stabilization of hydrogen-based superconductors limit their applications. So, the next challenge is to achieve room-temperature superconductivity at significantly low pressures, even ambient pressure. In this work, we design a series of high temperature superconductors that can be stable at moderate pressures by incorporating heavy rare earth elements Yb/Lu into sodalite-like clathrate hexahydrides. In particular, the critical temperatures (T_c) of Y₃LuH₂₄, YLuH₁₂, and YLu₃H₂₄ can reach 283 K at 120 GPa, 275 K at 140 GPa, and 288 K at 110 GPa, respectively. Their critical temperatures are close to or have reached room temperature, and minimum stable pressures are significantly lower than that of reported room temperature superconductors. Our work provides an effective method for the rational design of low-pressure stabilized hydrogen-based superconductors with room-temperature superconductivity simultaneously and will stimulate further experimental exploration.

In-situ electronic structure redistribution tuning of single-atom Mn/g-C3N4 catalyst to trap atomic-scale lead(II) for highly stable and accurate electroanalysis

Constructing catalysts with simple structures, uniform effective sites, and excellent performance is crucial for understanding the reaction mechanism of target pollutants. Herein, the single-atom catalyst of Mn-intercalated graphitic carbon nitride (Mn/g-C₃N₄) was prepared. It was found that the intercalated Mn atoms acted as strong electron donors to effectively tune the electronic structure distribution of the in-situ N atoms, providing a large number of negative potential atomic-scale sites for catalytic reactions. In the detection, the in-situ N atom established an electron bridge for the transient electrostatic trapping of free Pb(II), which induced Pb-N-Mn coordination bonding. Even in g-C₃N₄-loaded Mn nanoparticles, the N atom was again confirmed to be the interaction site for coupling with Pb. And the Mn^II-N₄-C/Mn^IV-N₄-C cycle actively participated in the electrocatalysis of Pb(II) was confirmed. Moreover, Mn/g-C₃N₄ achieved highly stable and accurate detection for Pb(II) with a sensitivity of 2714.47 µA·µM^-1·cm^-2. And excellent reproducibility and specific detection of real water samples made the electrode practical. This study contributes to understanding the changes in the electronic structure of chemically inert substrates after single-atom intercalation and the interaction between contaminants and the microstructure of sensitive materials, providing a guiding strategy for designing highly active electrocatalytic interfaces for accurate electroanalysis.

Alkaline-Earth Metal Effects on Physical Properties of Ferromagnetic AVO3 (A = Ba, Sr, Ca, and Mg): Density Functional Theory Insights

The effects of alkaline-earth metals on electronic, optical, thermodynamic, and physical properties of ferromagnetic AVO₃ (A = Ba, Sr, Ca, and Mg) have been investigated by first-principles calculations within the GGA+U formalism based on density functional theory. The optimized structural parameters are in good agreement with the available experimental results that evaluate the reliability of our calculations. The cell and mechanical stability is discussed using the formation energy and Born stability criteria, respectively. The mechanical behaviors of AVO₃ are discussed on the basis of the results of elastic constants, elastic moduli, Peierls stress, and Vickers hardness. The nature of the ductile-brittle transition of AVO₃ compounds was confirmed by the values of Pugh's ratio, Poisson's ratio, and Cauchy pressure. The electronic band structures, as well as density of states, reveal the half-metallic behavior of BaVO₃ and SrVO₃. However, CaVO₃ and MgVO₃ exhibit spin-gapless and magnetic semiconductor characteristics, respectively. The microscopic origin of the transition from the half-metallic to semiconductor nature of AVO₃ is rationalized using electronic properties. The presence of covalent, ionic, and metallic bonds in AVO₃ compounds is found by the analysis of bonding properties. The single-band nature of half-metallic AVO₃ is seen by observing hole-like Fermi surfaces in this study. Furthermore, the various thermodynamic and optical properties are calculated and analyzed. The refractive index suggests that AVO₃ could be a potential candidate for applications to high-density optical data storage devices.

Mg12O12 and Be12O12 Nanocages as Sorbents and Sensors for H2S and SO2 Gases: A Theoretical Approach

Theoretical calculations based on the Density Functional Theory (DFT) have been performed to investigate the interaction of H2S as well SO2 gaseous molecules at the surfaces of Be12O12 and Mg12O12 nano-cages. The results show that a Mg12O12 nano-cage is a better sorbent than a Be12O12 nano-cage for the considered gases. Moreover, the ability of SO2 gas to be adsorbed is higher than that of H2S gas. The HOMO-LUMO gap (Eg) of Be12O12 nano-cage is more sensitive to SO2 than H2S adsorption, while the Eg value of Mg12O12 nano-cage reveals higher sensitivity to H2S than SO2 adsorption. The molecular dynamic calculations show that the H2S molecule cannot be retained at the surface of a Be12O12 nano-cage within 300-700 K and cannot be retained on a Mg12O12 nano-cage at 700 K, while the SO2 molecule can be retained at the surfaces of Be12O12 and Mg12O12 nano-cages up to 700 K. Moreover, the thermodynamic calculations indicate that the reactions between H2S as well SO2 with Be12O12 and Mg12O12 nano-cages are exothermic. Our results suggest that we can use Be12O12 and Mg12O12 nano-cages as sorbents as well as sensors for H2S and SO2 gases.

Sensing Material-Dependent Interference of Multiple Heavy Metal Ions: Experimental and Simulated Thermodynamics Study on Cu(II), Cd(II), and As(III) Electroanalysis

Interference among multiple heavy metal ions (HMIs) is a significant problem that must be solved in electroanalysis, which extremely restricts the practical popularization of electrochemical sensors. However, due to the limited exploration of the intrinsic mechanism, it is still difficult to confirm the influencing factors. In this work, a series of experimental and theoretical electroanalysis models have been established to investigate the electroanalysis results of Cu(II), Cd(II), As(III), and their mixtures, which were based on the simple structure and stable coordination of nickel single-atom catalysts. X-ray absorption spectroscopy and density functional theory calculations were used to reveal the underlying detection mechanism of the 50-fold boosting effect of Cu(II) on As(III) while Cd(II) inhibits As(III). Combining the application of the thermodynamic model and Fourier transform infrared reflection, the specific interaction of the nanomaterials and HMIs on the interface is considered to be the fundamental source of the interference. This work opens up a new way of thinking about utilizing the unique modes of interplay between nanomaterials and HMIs to achieve anti-interference intelligent electrodes in stripping analysis.

Atomic Model of Gold Adsorption onto the Pyrite Surface with DFT Study

Adsorption mineralization of gold is an important mineralization mechanism under epigenetic and low temperature conditions. In this paper, a plane-wave pseudopotential method based on density functional theory (DFT) is used to explore the adsorption mechanism of gold on the surface of pyrite. Among the three surfaces of pyrite, the surface energies of (100), (111), and (210) surfaces are 1.0508, 1.5337, and 1.8255 J∙m2, respectively, and the (100) surface is the most stable surface in the thermodynamic state. The adsorption capacities of gold atoms under different surfaces are (210) (−2.68 eV) > (111) (−1.67 eV) > (100) (−0.84 eV). Mulliken analysis indicates that charge transfer occurs after the adsorption of gold atoms onto the surface of pyrite (210), and gold and iron atoms are oxidized with the reduction of sulfur atoms. The density of states (PDOS) analysis shows that the 5d orbital on the Fermi energy level of the iron atom is active and the adsorption capacity is greater than that of the sulfur atom, and adsorption is formed between the gold atom, which leads to the gold being able to be stably deposited on the surface of pyrite (210).

Sr[C2O5] is an Inorganic Pyrocarbonate Salt with [C2O5]2- Complex Anions

The synthesis of a novel type of carbonate, namely of the inorganic pyrocarbonate salt Sr[C₂O₅], which contains isolated [C₂O₅]^2--groups, significantly extends the crystal chemistry of inorganic carbonates beyond the established sp²- and sp³-carbonates. We synthesized Sr[C₂O₅] in a laser-heated diamond anvil cell by reacting Sr[CO₃] with CO₂. By single crystal synchrotron diffraction, Raman spectroscopy, and density functional theory (DFT) calculations, we show that it is a pyrocarbonate salt. Sr[C₂O₅] is the first member of a novel family of inorganic carbonates. We predict, based on DFT calculations, that further inorganic pyrocarbonates can be obtained and that these will be relevant to geoscience and may provide a better understanding of reactions converting CO₂ into useful inorganic compounds.

Combined DFT and Molecular Mechanics Modeling of the Adsorption of Semiconducting Molecules on an Ionic Substrate: PTCDA and CuPc on NaCl

Experimental results suggest that molecular geometry and energies can be influenced by the presence of thin film substrates as well as surrounding molecules. It is imperative that computational models take this influence into account. The accurate computational modeling of these molecules is an efficient way of carrying out chemistry calculations and reinforcing experimental findings. In our study, density functional theory (DFT) and molecular mechanics (MM) are used to model the configurations of the organic semiconducting materials, 3,4,9,10-perylene tetracarboxylic dianhydride, C₂₄H₈O₆ (PTCDA), and copper(II) phthalocyanine, C₃₂H₁₆CuN₈ (CuPc), as adsorbed on single- and double-layer NaCl substrates of various dimensions and charge settings. After a geometry and charge optimization of the molecules using DFT, the molecular geometries are optimized under different environments using computational calculations with specific force-field settings in HyperChem Professional 8.0(TM) software using MM. Energies and geometries of the molecules are then recorded, and our data are compared to experimental results of similar systems. We find that, with the appropriate choice of substrate properties, the calculated molecular configurations directly reflect those found experimentally. Our results support the idea that this method of simulation can produce reliable models in the field of physical chemistry.

First-principles study on the heterostructure of twisted graphene/hexagonal boron nitride/graphene sandwich structure

In recent years, the discovery of 'magic angle' graphene has given new inspiration to the formation of heterojunctions. Similarly, the use of hexagonal boron nitride, known as white graphene, as a substrate for graphene devices has more aroused great interest in the graphene/hexagonal boron nitride heterostructure system. Based on the first principles method of density functional theory, the band structure, density of states, Mulliken population, and differential charge density of a tightly packed model of twisted graphene/hexagonal boron nitride/graphene sandwich structure have been studied. Through the establishment of heterostructure models twisted bilayer-graphene inserting hBN with different twisted angles, it was found that the band gap, Mulliken population, and charge density, exhibited specific evolution regulars with the rotation angle of the upper graphene, showing novel electronic properties and realizing metal-insulator phase transition. We find that the particular value of the twist angle at which the metal-insulator phase transition occurs and propose a rotational regulation mechanism with angular periodicity. Our results have guiding significance for the practical application of heterojunction electronic devices.

Theoretical and experimental investigations of enhanced uranium(VI) adsorption by nitrogen doping strategy

With the ongoing development and utilization of nuclear energy, uranium pollution has become an increasingly serious issue. Although many adsorbents are able to remove hexavalent uranium (U(VI)) from aqueous solution,...

Density functional theory calculations of copper-doped rutile crystals: Local structural, electronic, optical, and electron paramagnetic resonance properties

The local structural, electronic, optical, and electron paramagnetic resonance (EPR) properties are uniformly studied for Cu²⁺ -doped rutile (TiO₂ ) crystals by using the density functional theory (DFT) calculations. The local cation-oxygen bond lengths and planar bond angle, band gap, Mulliken charge and overlapping population, density of state (DOS), and UV-Vis absorption spectra are calculated for pure and copper-doped rutile. The smaller overlapping population of Cu-O bonds in the doped system than Ti-O bonds in pure rutile reflects weaker orbital admixtures or covalency of the former. Compared with pure rutile, Cu²⁺ doping leads to significant redshift of the UV-Vis absorption band and the narrow impurity band in visible and near-infrared regions arising from the Cu²⁺ d-d transitions and narrowing of the band gap by about 0.636 eV, possibly suggesting enhancement of visible light activity. The Cu dopant induces a spin magnetic moment of 0.74 μB for the doped rutile. The calculated UV-Vis absorption spectra and spin Hamiltonian parameters for copper-doped rutile show reasonable agreement with the experimental data and some improvement related to the previous perturbation formula calculations. Present systematic studies would be helpful to understand the mechanisms of the enhancement in the optical and magnetic properties of this material with transition-metal (especially Cu²⁺ ) dopants.

Anionic Redox Regulated via Metal-Ligand Combinations in Layered Sulfides

The increasing demand for energy storage is calling for improvements in cathode performance. In traditional layered cathodes, the higher energy of the metal 3d over the O 2p orbital results in one-band cationic redox; capacity solely from cations cannot meet the needs for higher energy density. Emerging anionic redox chemistry is promising to access higher capacity. In recent studies, the low-lying O nonbonding 2p orbital was designed to activate one-band oxygen redox, but they are still accompanied by reversibility problems like oxygen loss, irreversible cation migration, and voltage decay. Herein, by regulating the metal-ligand energy level, both extra capacities provided by anionic redox and highly reversible anionic redox process are realized in NaCr_{1- y} V_y S₂ system. The simultaneous cationic and anionic redox of Cr/V and S is observed by in situ X-ray absorption near edge structure (XANES). Under high d-p hybridization, the strong covalent interaction stabilizes the holes on the anions, prevents irreversible dimerization and cation migration, and restrains voltage hysteresis and voltage decay. The work provides a fundamental understanding of highly reversible anionic redox in layered compounds, and demonstrates the feasibility of anionic redox chemistry based on hybridized bands with d-p covalence.

Hierarchical Modulation on Optical Anisotropy Driven by Metal Cation Polyhedra in Fluorooxoborates MIIB4O6F2 (MII = Be, Mg, Pb, Zn, Cd)

The enhancement mechanism of birefringence is very important to modulate optical anisotropy and materials design. Herein, the different cations extending from alkaline-earth to alkaline-earth, d 10 electron configuration, and 6s 2 lone pair cations are highlighted to explore the influence on the birefringence. A flexible fluorooxoborate framework from AEB 4 O 6 F 2 (AE = Ca, Sr) is adopted for UV/deep-UV birefringent structures, namely, M II B 4 O 6 F 2 (M II = Be, Mg, Pb, Zn, Cd). The maximal enhancement on birefringence can reach 46.6% with the cation substitution from Ca, Sr to Be, Mg ( route-I ), Pb (route-II), and Zn, Cd (route-III). The influence of the cation size, the stereochemically active lone pair, and the binding capability of metal cation polyhedra is investigated for the hierarchical improvement on birefringence. Significantly, the BeB 4 O 6 F 2 structure features the shortest UV cutoff edge 146 nm among the available anhydrous beryllium borates with birefringence over 0.1 at 1064 nm , and the PbB 4 O 6 F 2 structure has the shortest UV cutoff edge 194 nm within the reported anhydrous lead borates that hold birefringence larger than 0.1 at 1064 nm. This work sheds light on how metal cation polyhedra modulate birefringence, which suggests a credible design strategy to obtain desirable birefringent structures by cation control.

Effect of Lattice Substitution on Adsorption of Hexavalent Chromium by Montmorillonite, Nontronite, and Beidellite

This work aims to evaluate the effect of lattice substitution on adsorption of hexavalent chromium by three kinds of typical clay minerals, and its common isomorph via experiments and calculations were performed based on density functional theory. The experiments (25 °C, 4 h, pH = 4 and without stirring) confirmed an order of adsorption capacity as follows: Montmorillonite (12 mg/g) > Nontronite (9 mg/g) > Beidellite (8 mg/g). Accordingly, the Mulliken populations, density of states, and band structures of the mineral models with the structural Al, Mg, Fe(II), Fe(III), and Al (in tetrahedrons) on behalf of five species of isomorph were calculated. The calculation results explain the differences between hexavalent chromium adsorption capacity of five kinds of isomorph by means of atom, key populations, overlapping valence electron orbitals, and the variation of energy band. However, no overlapping orbitals were observed in the adsorption system with structural Mg. It is implied that the structural Mg has little influence of hexavalent chromium adsorption. In conclusion, our study contributes to achieving a better understanding of modified clay minerals materials applications.

The effect of metal substitution in CsSnI3 perovskites with enhanced optoelectronic and photovoltaic properties

Non-toxic lead-free halide metal perovskites have gained significant interest in photovoltaic and optoelectronic device applications. In this manuscript, we have studied the structural, electronic, mechanical, and optical properties of eco-friendly cubic CsSn_1-x Cu _x I₃, (x = 0, 0.125, 0.25, 0.5, 1) perovskites applying first-principles pseudopotential-based density functional theory (DFT). Cu-doped CsSnI₃ has a large impact on the band gap energy viz. the transition of direct band gap towards the indirect band gap. The mechanical properties demonstrate that the pristine and Cu-doped CsSnI₃ samples are mechanically stable and their ductility is enhanced by Cu doping. The mechanical stability and ductility favors the suitability of pure and Cu-doped samples in the thin film industry. The absorption edge of Cu-doped CsSnI₃ moves towards the lower energy region in comparison with their pure form. In addition, the high dielectric constant, high optical absorption, and high optical conductivity of Cu-doped CsSnI₃ materials suggests that the studied materials have a broad range of applications in optoelectronic devices, especially solar cells. A combined analysis of the structural, electronic, mechanical and optical properties suggests that CsSn_1-x Cu _x I₃, (x = 0, 0.125, 0.25, 0.5, 1) samples are a suitable candidate for photovoltaic as well as optoelectronic device applications.

An Investigation on Substitution of Ag Atoms for Al or Ti Atoms in the Ti2AlC MAX Phase Ceramic Based on First-Principles Calculations

The present work introduced first-principles calculation to explore the substitution behavior of Ag atoms for Al or Ti atoms in the Ti₂AlC MAX phase ceramic. The effect of Ag substitution on supercell parameter, bonding characteristic, and stability of the Ti₂AlC was investigated. The results show that for the substitution of Ag for Al, the Al-Ti bond was replaced by a weaker Ti-Ag bond, decreasing the stability of the Ti₂AlC. However, the electrical conductivity of the Ti₂AlC was enhanced after the substitution because of the contribution of Ag 4d orbital electrons toward the density of states (DOS) at the Fermi level coupled with the filling of Ti d orbital electrons. For the substitution of Ag for Ti, new bonds, such as Ag-Al bond, Ag-C bond, Al-Al bond, Ti-Ti anti-bond, and C-C anti-bond were generated in the Ti₂AlC. The Ti-Ti anti-bond was strengthened as well as the number of C-C anti-bond was increased with increasing the substitution ratio of Ag for Ti. Similar to the substitution of Ag for Al, the stability of the Ti₂AlC also decreased because the original Al-Ti bond became weaker as well as the Ti-Ti and C-C anti-bonds were generated during the substitution of Ag for Ti. Comparing with the loss of Ti d orbital electrons, Ag 4d orbits contributed more electrons to the DOS at the Fermi level, improving the electrical conductivity of the Ti₂AlC after substitution. Based on the calculation, the substitution limit of Ag for Al or Ti was determined. At last, the substitution behavior of Ag for Al or Ti was compared to discriminate that Ag atoms would tend to preferentially substitute for Ti atoms in Ti₂AlC. The current work provides a new perspective to understand intrinsic structural characteristic and lattice stability of the Ti₂AlC MAX phase ceramic.

Understanding the anchoring and catalytic effect of the Co@C2N monolayer in lithium-selenium batteries: a first-principles study

The practical applications of lithium-selenium (Li-Se) batteries are impeded due to the low utilization of active selenium, sluggish kinetics, and volume change. The development of highly efficient host materials to suppress high-order polyselenide shuttling and accelerate Li₂Se conversion is essential for Li-Se batteries. Herein, a theoretical design of a Co@C₂N monolayer as a host material for ultra-high areal capacity Li-Se batteries is proposed by first-principles calculations. The investigations of the lowest energy configurations, binding energies, and the charge transfer indicate that the Co@C₂N monolayer could alleviate the reciprocating motion of high-order polyselenides and improve the cycling performance. Further electronic property calculations show that the semi-metallic characteristics of the Co@C₂N monolayer material are retained even after chemical adsorption with Se₈ or Li₂Se_n molecules, which is beneficial for the utilization of active selenium. In addition, the crucial catalytic role of the Co@C₂N monolayer is investigated and the results indicate that the Co@C₂N monolayer could facilitate the formation and decomposition of Li₂Se molecules during the discharge and charge processes. Our present work would not only provide a deep understanding on the anchoring and catalytic effect of the Co@C₂N monolayer, but also demonstrate a general principle for the rational design and screening of advanced materials for high energy density Li-Se batteries.