First-principles Density Functional Theory Research Articles

Large-Scale DFT Calculations on Size and Site Dependences of Atomic and Electronic Structures in Metallic Nanoparticle Catalysts

Size control of Pt nanoparticle catalysts is one of the key challenges in fuel cell development. Miniaturization of Pt nanoparticles is expected to increase activity and save the amount of Pt, while very small particles (e.g. sub-nano particles or clusters) have different electronic structures and stabilities from “nano” particles. To investigate the atomic and electronic structures of materials, first-principles density functional theory (DFT) calculation is a powerful tool. However, because of its high computational cost, the DFT applications have been limited mainly for small particles and clusters of tens to hundreds of atoms. In this study, by using our own large-scale DFT calculation method, we investigate the size and site dependences of atomic and electronic structures in Pt nanoparticles with the diameters of several nanometers, which are comparable to the sizes of the particles in practical use.The computational cost of the conventional DFT calculation methods scale cubically to the system size, i.e., the number of the atoms in the target system and the number of local functions for each atom, which are used to express electronic density. We have developed the multi-site support function (MSSF) method [1,2], in which local functions are constructed as the linear combinations of the atomic orbital functions belonging to not only the target atom but also its neighboring atoms. The MSSF method enables us to reduce the number of local functions to be the minimal-basis size, leading the dramatical computational cost reduction. The MSSF method is implemented in our large-scale DFT code CONQUEST [3,4].We optimized the structures of Pt nanoparticles with the diameters of 0.5 nm (13 atoms) - 5.5 nm (3871 atoms) and found that the Pt-Pt bond lengths inside the nanoparticle converge to those in bulk Pt when the nanoparticle size becomes large. The similar trend is found also in the electronic structures as shown in the figure. In the presentation, we compare the size dependence of the stability and atomic and electronic structures of Pt nanoparticle with other metallic nanoparticles. Site dependence of the electronic structures and reactivity with molecules are also investigated by using large-scale DFT together with statistical analysis.[1] A. Nakata, D. R. Bowler, T. Miyazaki, J. Phys. Soc. Jpn., 91, 091011 (2022). [2] A. Nakata, D. R. Bowler, T. Miyazaki, Phys. Chem. Chem. Phys. 17, 31427 (2015). [3] http://www.order-n.org/ [4] A. Nakata, J. S. Baker, S. Y. Mujahed, J. T. L. Poulton, S. Arapan, J. Lin, Z. Raza, S. Yadav, L. Truflandier, T. Miyazaki, D. R. Bowler, J. Chem. Phys., 152, 164112 (2020). Figure 1

Hierarchical Dual-Carbon Anode and Cathode Derived from Zeolitic Imidazolate Frameworks Grown on 3D Graphene Oxide Aerogels for Ultrahigh-Performance Potassium-Ion Hybrid Energy Storage Systems

A potassium-ion hybrid system has been shown to be highly suitable for dual-mode applications as both a battery and a supercapacitor, once the issues of slow kinetics in the anode and low capacity in the cathode are addressed. In this study, we design a Potassium-ion hybrid energy storage (PIHES) system that excels in both rapid charging and high energy density. The PIHES full cells are developed using zeolitic imidazolate frameworks (ZIFs) grown on 3D graphene oxide aerogels (RGOAs). These microporous ZIFs on 3D RGOAs form a Zn-embedded hierarchical porous graphitic carbon anode material. Sub-nanometer Zn particles in the anode facilitate rapid faradaic reactions, as confirmed by operando X-ray diffraction studies combined with kinetic analysis. The hierarchical structure of the material, with its porosity and graphitization, promotes the efficient transport of ions and electrons. First-principles density functional theory calculations reveal the underlying mechanism of potassium's superior adsorption behavior on sub-nanometer Zn nanoparticles compared to other materials, resulting in high-rate capability. The Zn-embedded ZIF-derived hierarchical porous carbon (ZZHPC) offers approximately twice the capacity of pristine ZIFs. Our cathode materials are derived from the graphitic carbon production and Zn evaporation from ZIFs on 3D RGOAs, featuring N-rich microporous sites for high capacity, excellent electrolyte wettability, and mesoporous graphitic carbon channels for rapid ion and electron transport. Our potassium-ion hybrid capacitor, utilizing a ZZHPC anode and a ZIF-derived hierarchical porous carbon (ZHPC) cathode, achieves an unprecedented energy density of 207.5 Wh kg-1 and a fast-chargeable power density of 21,500 W kg-1, while maintaining nearly 100% Coulombic efficiency over 10,000 cycles.

Fast-Charging Li4Ti5O12 Anode Driven By Light

The development of fast-charging lithium-ion batteries (LIBs) is crucial for achieving significant market adoption of electric vehicles (EVs). The successful achievement of fast-charging LIBs depends on efficient charge transfer and the diffusivity of lithium ions. The photo-assisted battery system exhibits promising fast-charging properties. Previous research has shown that direct exposure to white light can induce a more oxidized center in a spinel LiMn2O4 (LMO) cathode, accelerating its charging rate.[ 1] Recently, our group found that illumination with red light on an operating LMO cathode induces an Mn d-d electron excitation, simultaneously shrinks the Mn-Mn lattice, and facilitates faster delithiation of the LMO cathode.[ 2] Consequently, the charging time of the battery decreases. This encourages us to consider whether the photon energy from a specific wavelength of light can also enhance the lithiation process on the anode side. Spinel Li4Ti5O12 (LTO) is a promising material for faster-charging anodes due to its small volume charge and high-rate capability in lithium intercalation. However, the system displays slow lithium diffusivity due to poor bulk ionic conductivity. To examine the photon effect of light on these anodes, we demonstrate the photo-accelerated fast-charging (lithiation process) mechanism with an LTO spinel anode.The thin film LTO's energy band gap (Eg), approximately 3.4 eV, was determined through intense UV-visible (UV-Vis) absorption spectrum analysis, assessed in a transmission mode employing Tauc’s Law. This indicates that an LED light with photon energy around 3.4 eV might trigger rapid charging by exciting electron transfer to the T-t2g band. To explore the impact of light on the fast-charging behavior of the LTO electrode, current was measured while applying a constant voltage of 1.2 V. During the 20-minute chronoamperometry experiment, utilizing the 3.4 eV UV LED to illuminate the cell resulted in a progressive increase in current. This current increase peaked at approximately 200s, leading to a maximum average capacity increase of 13 mA h g-1. This suggests that UV illumination accelerates the lithiation process compared to the dark state, particularly favoring the early lithiation stage. Subsequently, a red LED emitting 2 eV photon energy was used to illuminate the same cell, resulting in no discernible change in current levels compared to the dark state. Electrochemical impedance spectroscopy (EIS) further revealed a significant reduction in charge transfer resistance of the window cell when illuminated with UV light compared to both the dark state and red illumination. This alteration in electrode reaction kinetics at the interface suggests a distinct influence of different light wavelengths on the charging process.In addition to assessing charge transfer at the electrode interface, galvanostatic intermittent titration technique (GITT) analysis was conducted at a 2 C rate to further elucidate diffusion within the LTO electrode. The GITT curves reveal that the diffusion of Li+ ions was approximately 1.3 times faster when the cell was illuminated by UV light compared to dark conditions. Consequently, we deduce that photo-accelerated fast charging can also occur during the lithiation process (reduction reaction) of anode materials, driven by optical forces.To delve into the underlying mechanisms, we conducted first-principles density functional theory (DFT) calculations. The outcomes revealed that the generation of additional electrons in LTO results in a reduction in the bandgap and shifts the Fermi level above the conduction band minimum, effectively transforming LTO into an active conductor of electricity. These calculations indicate that UV light illumination has the capability to surmount the bandgap of LTO, generating electron-hole pairs and thereby facilitating charge transfer and lithium-ion diffusion.In conclusion, our study showcased that UV light illumination on the LTO anode can lead to a faster charging speed of approximately 17% compared to dark conditions. We posit that the observed phenomenon of photo-accelerated fast charging in LTO is linked to the formation of electron-hole pairs in intrinsically wide-bandgap insulators or semiconducting materials. This discovery holds considerable implications for the advancement of fast charging technologies for lithium-ion batteries, potentially mitigating range anxiety concerns and facilitating the widespread adoption of electric vehicles.Acknowledgments: This work was supported by funding from Royal Dutch Shell plc. Argonne National Laboratory operates under contract no. DE-AC02-06CH11357 with the U.S. Department of Energy Office of Science. We gratefully acknowledge use of the Bebop or Swing or Blues cluster in the Laboratory Computing Resource Center at Argonne National Laboratory and supported by the U.S. Department of Energy Office of Science.Reference[1] A. Lee et al., Nat. Commun., 10, 4946 (2019).[2] J. Lipton et al., Cell Reports Physical Science, 3, 101051 (2022).

Spectral Design of Nano-Cerates for Emerging Passive Radiative Cooling Technologies: Theory Boosts Experiments.

Cerate nanoceramics have been recently considered to be key materials for radiative thermal management and enhanced solar reflectance. Herein, we demonstrate by means of first-principles density functional theory calculations how experimentally prepared La2Ce2O7 and Al2Ce2O7 materials with defective fluorite structure exhibit superior temperature stability, strong UV-vis/near-infrared reflectance, and tunable mid-infrared emissivity, thus representing excellent host matrices for doping-controlled chromatic and thermal properties. By means of phonon dispersion analysis, we demonstrate how disorder and aluminum impurities induce locally distorted chemical environments that can be exploited for achieving selective infrared emittance for passive radiative cooling devices.

High-pressure characterization of Ag3AuTe2: Implications for strain-induced band tuning

Recent band structure calculations have suggested the potential for band tuning in the chiral semiconductor Ag3AuTe2 to zero upon application of negative strain. In this study, we report on the synthesis of polycrystalline Ag3AuTe2 and investigate its transport and optical properties and mechanical compressibility. Transport measurements reveal the semiconducting behavior of Ag3AuTe2 with high resistivity and an activation energy Ea of 0.2 eV. The optical bandgap determined by diffuse reflectance measurements is about three times wider than the experimental Ea. Despite the difference, both experimental gaps fall within the range of predicted bandgaps by our first-principles density functional theory (DFT) calculations employing the Perdew–Burke–Ernzerhof and modified Becke–Johnson methods. Furthermore, our DFT simulations predict a progressive narrowing of the bandgap under compressive strain, with a full closure expected at a strain of −4% relative to the lattice parameter. To evaluate the feasibility of gap tunability at such substantial strain, the high-pressure behavior of Ag3AuTe2 was investigated by in situ high-pressure x-ray diffraction up to 47 GPa. Mechanical compression beyond 4% resulted in a pressure-induced structural transformation, indicating the possibility of substantial gap modulation under extreme compression conditions.

First-principles calculation of the effects of In doping on η-Cu6Sn5 structure, elastic anisotropy, electronic properties and fracture toughness

During the welding and service stages, the anisotropy of Cu6Sn5 between tin solder / Cu solder joints will lead to abnormal grain growth and fracture of Cu6Sn5, which will eventually lead to solder joint failure, so it is very important to study the alloying element indium (In) to reduce the anisotropy of Cu6Sn5. The effects of indium doping on the crystal structure, electronic structure and mechanical properties of η-Cu6Sn5 have been studied systematically by means of first-principles density functional theory. Through calculation, it is found that with the change of indium doping position, the crystal structure is slightly deformed, but remains stable. Indium doping changes the electronic structure of η-Cu6Sn5, and a new bonding peak is formed by the hybridization of Cu-d and In-s around −5.9 eV. In addition, indium doping can significantly increase the mechanical properties of η-Cu6Sn5, including elastic modulus and hardness. Indium significantly reduces the anisotropy of η-Cu6Sn5, and the anisotropy decreases by nearly 80 % at most. At the same time, the addition of indium can increase the fracture toughness of η-Cu6Sn5.

Superconductivity and strain-enhanced phase stability of Janus tungsten chalcogenide hydride monolayers

Janus transition metal-dichalcogenide materials have attracted a great deal of attention due to their remarkable physical properties arising from the two-dimensional geometry and the breakdown of the out-of-plane symmetry. Using first-principles density functional theory, we investigated the phase stability, strain-enhanced phase stability, and superconductivity of Janus WSeH and WSH. In addition, we investigated the contribution of the phonon linewidths from the phonon energy spectrum responsible for the superconductivity and the electron-phonon coupling as a function of phonon wave vectors and modes. Previous work has examined hexagonal 2H and tetragonal 1T structures, but we found that neither is a ground-state structure. The metastable 2H phase of WSeH is dynamically stable with Tc≈11.60K, similar to WSH. Compressive biaxial strain—the two-dimensional equivalent of pressure—can stabilize the 1T structures of WSeH and WSH with Tc≈9.23K and 10.52 K, respectively. Published by the American Physical Society 2024

Electrical and work function-based chemical gas sensors utilizing NC3 and graphene combination

Research has been conducted on the potential practical uses of heterostructures made of graphene and carbon nitride (NC3) following their successful synthesis. The remarkable gas sensing properties of these 2D nanosheets have captured significant interest, attributed to distinctive electronic characteristics and exceptional surface-to-volume ratio that are resulted from combination of NC3 and graphene. In this study, we present a detailed analysis of electronic and structural features of pristine NC3 and graphene (PG), and their in-plane heterostructures using first-principles density functional theory. Our investigation utilizes the B3LYP and dispersion-corrected van der Waals (vdW) functional WB97XD, along with 6-311G (d, p) basis set. Our findings indicate that the nanosheets we anticipated exhibit robust structural stability, characterized by a desirable cohesive energy. Furthermore, we observed a gradual increase in the bandgap as the concentration of N–C in the nanosheets increases. Additionally, we investigated the adsorption characteristics of these heterostructures towards toxic gas molecules such as SO2 and CO. Among the studied heterostructures, GNC3I demonstrated higher adsorption energy (Eads), with values of approximately −0.283 and −0.491 eV when exposed to SO2 and carbon monoxide gas molecules respectively. Electronic characteristics, including LUMO and HOMO energy values, energy gap (Eg) between HOMO and LUMO, work function, Fermi level, and conductivity, underwent notable modifications upon SO2 gas adsorption over nanosheets, except for PG. However, these parameters remained relatively unchanged following carbon monoxide adsorption. Natural bond orbital (NBO) and Mulliken charge analysis demonstrates that there is a transfer of charge from gas molecules to nanosheets. Although nanosheets exhibit slightly higher adsorption energy (Eads) values for CO gas compared to SO2 gas, various assessments, including molecular electrostatic potential (MEP) mapping, electronic properties, and charge transfer (CT) analysis, suggest that these nanosheets are superior sensors for detecting SO2 gas rather than carbon monoxide gas molecules.

Tailoring hydrogen adsorption via charge transfer at bimetallic Cr0.48Ru0.52 alloy nanoparticles decorated on carbon nanofiber for enhanced hydrogen evolution catalysis

Designing and synthesizing highly efficient and stable electrocatalysts for the hydrogen evolution reaction (HER) is crucial for the practical and large-scale application of hydrogen sources. Recent research has focused on tuning the electronic structure of electrocatalysts to achieve optimal HER activity, with particular emphasis on interfacial engineering to induce electron transfer and optimize HER kinetics. In this study, as part of research into heterointerface engineering, bimetallic Cr0.48Ru0.52 alloy nanoparticles decorated on carbon nanofibers (Cr0.48Ru0.52/CNFs) were fabricated through a simple electrospinning and post-calcination process to serve as an efficient alkaline HER catalyst. The Cr0.48Ru0.52/CNFs demonstrated exceptional electrocatalytic HER performance, with an overpotential of only 13 mV at −10 mA cm−2 and a Tafel slope of 60.8 mV dec−1, indicating high catalytic activity compared to commercial benchmark catalysts (i.e., Ru/C and Pt/C). First-principles density functional theory calculations support these results, revealing that Cr0.48Ru0.52 balances proton reduction (Volmer step) and H∗ desorption (Tafel/Heyrovsky step) processes during electrocatalysis, as evidenced by the near-zero hydrogen adsorption (ΔGH∗) value (ca. −0.11 eV). Therefore, this study highlights that Cr0.48Ru0.52/CNFs, with noble Ru comprising only half of the total metal content, can promote optimal HER kinetics under alkaline condition.

Polyvinyl fluoride: Predicting polarization in a complex soft matter system

We use first-principle density functional theory (DFT) to predict properties for semicrystalline polyvinyl fluoride (PVF) and compare with polyvinylidiene fluoride. We note that the crystalline regions of PVF are complex in the sense that we lack a complete experimental characterization of the detailed atomic organization. We therefore turn to DFT to predict both the structure and associated materials properties, illustrating a possible work flow for complex soft-matter modeling. We rely on the nonempirical consistent-exchange van der Waals density functional version [K. Berland and P. Hyldgaard, ] and identify plausible ground-state and excited-state motifs. From there we predict the elastic response of the crystalline motifs, and an upper limit estimate of the PVF polarization at room temperature. Published by the American Physical Society 2024

Theoretical Calculation of Dissolved Gas in Transformer Oil Using the Gas Sensitive Properties of Sc- and Ti-Modified ZrS2.

To guarantee the secure functioning of the complete power system and minimize the risks associated with oil-filled transformers during their operation, it is greatly important to carry out gas sensing studies of dissolved gases in transformer research. Through the utilization of first-principles density functional theory calculations, the adsorption energy, electronic characteristics, and recuperation duration of ZrS2 modified with Sc and Ti were examined. The results show that compared to those of the initial ZrS2 material, the doping of TM atoms Sc and Ti significantly improved the adsorption properties of the material, and the adsorption of CO and C2H4 showed chemisorption. The adsorption capacity for gases decrease in the following order: C2H4 > CO > H2. The calculated recovery times indicate that Sc-ZrS2 and Ti-ZrS2 were ideal carbon monoxide sensing materials under the specific conditions. The results of this work can establish a fundamental rationale for the use of ZrS2 in sensing the conditions of oil-immersed transformers.

Two-dimensional pnictogen carbides and their Janus structures: Potential on visible-light photocatalytic water splitting for hydrogen production

This study explored eight novel and highly stable monolayer configurations: C3X2 (X = N, P, As, Sb, and Bi) and C3XY (X = P and As, YAs and Sb) by analyzing their electronic, optical, and photocatalytic properties based on first-principles density functional theory. The findings indicated that the C3X2 monolayers, except for C3Bi2, exhibit indirect band gap semiconductor properties, and their band gaps are 1.497, 1.862, 2.272, 1.448, and 1.561 eV, respectively. Notably, only C3P2 and C3As2 fulfilled the prerequisites for photocatalytic water splitting, boast high electron mobility (up to ∼103 cm2/Vs), strong absorption in the visible light range, and high solar-to-hydrogen (STH) efficiency (30.16% for C3P2 and 23.05% for C3As2). Moreover, the Janus C3PAs, C3PSb, and C3AsSb monolayers exhibited indirect band gaps ranging from 1.616 to 2.070 eV and satisfied the band structure criteria for photocatalytic water splitting. These three Janus monolayers outperformed C3X2 in terms of optical absorption, carrier mobility, and STH efficiency owing to their inherent electric fields. The STH efficiency of C3PSb and C3AsSb reach 31.26% and 29.17%, respectively, with electron mobility reaching up to 4642.01 and 11902.64 cm2/Vs, respectively, indicating their exceptional potential for photocatalytic water splitting.

Investigation of optoelectronic, mechanical and thermodynamic properties of cubic perovskite FrBCl3 (B = Zn, Cd) in approach of density functional theory

Lead-free cubic metallic halide perovskite (MHP) compounds, FrBCl3 (where B = Zn, Cd), have been evaluated using first-principles density-functional theory (DFT). Both FrZnCl3 and FrCdCl3 satisfy the stability conditions determined by their tolerance and octahedral factors. These materials demonstrate the characteristics of indirect band gap semiconductors, and their high optical absorption coefficients create promising opportunities for the advancement of optoelectronic devices. The elastic properties of both perovskites indicate robust mechanical stability, while their ductility, flexibility, and stiffness suggest potential for thin film fabrication. Furthermore, the Debye temperature profile underscores the thermal stability of these compounds. This computational study reveals coherent relationships among their structural, electronic, optical, mechanical, and thermodynamic properties. Consequently, these materials may offer exciting applications in nuclear medicine, X-ray imaging, and a variety of optoelectronic devices.

Strain effect on the physical properties of novel Mg3NI3 perovskite material: First principle DFT analysis

Inorganic perovskite-based substances have become a major attraction to solar technology. Inorganic cubic Mg3NI3 perovskites have generated a heap of fascination owing to their distinctive optical, electrical, and structural features. The photovoltaic and optoelectronic industries prioritize lead-free, atomically tailored metal halide perovskites due to the need to address lead (Pb) toxicity and instability. This study assessed the optical, structural, and electrical parameters of Pb-free inorganic halide perovskites Mg3NI3 as a function of biaxial compressive and tensile strain, leveraging first-principles density-functional theory (FP-DFT). Refractive index, absorption coefficient, reflectivity, dielectric function, and tolerance factor are a few additional optical parameters that are computed and processed. The bandgap of the planar Mg3NI3 molecule is 0.412 eV (PBE) when SOC is not applied. The bandgap reduces to 0.363 eV (PBE) at its Γ(gamma) and R-point when the subjective SOC effect is taken into consideration. This compound's bandgap will narrow under tensile strain and expand under compressive strain, depending on whether the SOC effect is applied or not. Several elastic factors are anticipated, including the bulk modulus, Pugh's ratio, elastic constants, anisotropic factors, and Poisson's ratio. Electronic property calculations using band mechanism and density of states (DOS) suggest that Mg3NI3 have a bandgap that is indirect and semiconductive. The elastic properties of this material were found to be mechanically stable, anisotropic, and ductile. In the photon energy range suitable for solar cells, the spikes in the dielectric constant of Mg3NI3 are seen. Our findings point to the prospect of Mg3NI3 as a non-toxic, high-performance, low-cost material for implementation in solar cells and different semiconductor devices.

Phase-Engineered Transition Metal Dichalcogenides for Highly Efficient Surface-Enhanced Raman Scattering.

Phase engineering of two-dimensional (2D) transition metal dichalcogenides (TMDs) is an attractive avenue to construct new surface-enhanced Raman scattering (SERS) substrates. Herein, 2D WS2 and MoS2 monolayers with high-purity distorted octahedral phase (1T') are prepared for highly sensitive SERS detection of analytes (e.g., rhodamine 6G, rhodamine B and crystal violet). 1T'-WS2 and 1T'-MoS2 monolayers show the detection limits of 8.28 × 10-12 and 8.57 × 10-11 M for rhodamine 6G, with the enhancement factors of 4.6 × 108 and 3.9 × 107, respectively, which are comparable to noble-metal substrates, outperforming semiconducting 2H-W(Mo)S2 monolayers and most of the reported non-noble-metal substrates. First-principles density functional theory calculations show that their Raman enhancement effect is mainly ascribed to highly efficient interfacial charge transfer between the 1T'-W(Mo)S2 monolayers and analytes. Our study reveals that 2D TMDs with semimetallic 1T' phase are promising as next-generation SERS substrates.

Tuning the Electronic Bandgap of Penta-Graphene from Insulator to Metal Through Functionalization: A First-Principles Calculation.

We performed first-principles density functional theory (DFT) calculations to numerically investigate the electronic band structures of penta-graphene (PG), a novel two-dimensional carbon material with a pentagonal lattice structure, and its chemically functionalized forms. Specifically, we studied hydrogenated PG (h-PG), fluorinated PG (f-PG), and chlorinated PG (Cl-PG). We used the generalized gradient approximation (GGA) and the hybrid Heyd-Scuseria-Ernzerhof (HSE06) exchange-correlation functional in the DFT-based software VASP to capture electronic properties accurately. Our results indicate that hydrogenation and fluorination increased the indirect bandgap of PG from 3.05 eV to 4.97 eV and 4.81 eV, respectively, thereby effectively transforming PG from a semiconductor to an insulator. In contrast, we found that chlorination closed the bandgap, thus indicating the metallic behavior of Cl-PG. These results highlight the feasibility of tuning the electronic properties of PG through functionalization, offering insight into designing new materials for nanoelectronic applications.

First-principles density functional study of iodine molecule adsorption on stable CuS surfaces

The present work investigated the adsorption of gaseous iodine molecules (I2) on stable CuS surface, which has demonstrated excellent performance as an adsorbent for I2 removal, with first-principles density functional theory (DFT). In this work, a pair of asymmetric surfaces (marked as slab1 and slab2) formed by breaking the weakest bond along (001) direction are chosen to present CuS surfaces. The findings indicate that the adsorption of I2 molecules on the pristine CuS(001) surface is relatively weak, while surface defects significantly enhance the binding strength of I2. In particular, S-vacancy CuS(001) surfaces exhibit considerably higher adsorption energy for I2 compared to Cu-vacancy surfaces. We found that the hollow and Cu-top sites are typically the dominant adsorption sites, and the initial orientation of I2 relative to the surface also influences the adsorption performance.

A Density Functional Theory Study on the Adsorption of Methyl Mercury and Arsenous Acid on Cellulose Chain

Methyl mercury (MeHg) and arsenous acid (H3AsO3) are toxic chemicals that pollute freshwater sources. Driven by this environmental concern, developing efficient, eco-friendly, adsorbent materials has become necessary. Using first-principles density functional theory, we decipher the fundamental adsorption mechanism of MeHg and H3AsO3 on the cellulose biopolymer. The interaction is mainly described as physisorption by considering various bonding sites and orientations of MeHg and H3AsO3 on the cellulose chain. According to the binding energy, H3AsO3 interacts more strongly with cellulose than MeHg. The hydrogen bonding between H3AsO3 and the functional groups of cellulose plays an important role in the adsorption strength. Whereas MeHg does not form a hydrogen bond with the functional groups, the adsorption is mainly described as an induced dipole. These claims are further supported by careful analysis of the electronic redistribution via Charge Density Difference, Bader charge analysis, and Electron Localization Function. Overall, the results revealed that cellulose is a competitive material for trapping H3AsO3owing to its abundance in oxygen-functional groups. The findings presented here proposed the adsorption mechanism MeHg and H3AsO3 on the cellulose biopolymer. This work will be the basis for developing cellulose-based adsorbent material and bridging the gap in the literature.

Impact of Calcium Doping on the Electronic and Optical Characteristics of Strontium Hydride (SrH2): A DFT Study

This study investigates the electronic and optical properties of calcium-doped strontium hydride (SrH2) using first-principles density functional theory (DFT) calculations via the CASTEP code with generalized gradient approximation (GGA). We explore the impact of calcium (Ca) doping on the electronic band structure, density of states (DOS), and optical absorption spectra of SrH2. Our results show that Ca doping significantly alters the electronic properties of SrH2, notably increasing the indirect bandgap from 1.3 eV to 1.6 eV. The DOS analysis reveals new states near the Fermi level, primarily from Ca 3d orbitals. Moreover, the optical absorption spectra display enhanced absorption in the visible range, suggesting the potential for optoelectronic applications. This research highlights the feasibility of tuning the electronic and optical characteristics of SrH2 through Ca doping, thus opening the way for the generation of advanced materials with tailored properties.

Highly efficient magnesium ferrite/graphene nano-heterostructure for visible-light photocatalytic applications: Experimental and first-principles DFT studies

In this research study, the electronic structure of magnesium ferrite/graphene (MFO/Gr) nano-heterostructure for photocatalytic application was studied. The MFO nanoparticles with a median size of 85 nm were composited with Gr sheets using a photo-assisted reduction process. The XRD and SAED results, respectively, showed the spinal crystalline structure of MFO and the hexagonal structure of Gr in MFO/Gr nanocomposite. The XPS results revealed that the orbitals of MFO and Gr atoms interacted with each other, implying a Van der Waals heterojunction nanocomposite. The optical characteristics using UV–Vis diffuse reflectance spectrophotometry (UV–Vis DRS) and photoluminescence (PL) spectra demonstrated a lowering of MFO band gap from 2.05 to 1.84 eV by incorporation of Gr. Furthermore, the photoelectrocatalytic and photocatalytic dye degradation examinations showed a substantial impact of Gr on the photocatalytic activity of MFO nanoparticles: a 28-fold increase in the photocurrent and an 8-fold increase in the dye-degradation rate. The density functional theory (DFT) studies on MFO/Gr heterojunction revealed a considerable hybridization between Gr atoms orbitals (2p orbitals) and MFO atoms orbitals (Mg 3 s and Fe 3d orbitals) in the conduction band, which facilitate the transfer of photo-excited electrons from MFO to Gr. Also, the charge density difference at the MFO/Gr interface led to a polarized field at the interface, which is desirable for hindering photogenerated electron-hole recombination in the MFO/Gr nanocomposite. Along with the experimental results, the DFT results also revealed that the MFO/Gr nano-heterostructure is an excellent candidate for photocatalytic applications such as water splitting using sunlight to produce green hydrogen fuel.