Orbitals Of Cations Research Articles

Occupied Outer Cationic Orbitals in Dimeric MX2‐Type BaSe2 Compound Lead to Reduced Thermal Conductivity and High Thermoelectric Performance

Occupied Outer Cationic Orbitals in Dimeric <scp>MX₂</scp>‐Type <scp>BaSe₂</scp> Compound Lead to Reduced Thermal Conductivity and High Thermoelectric Performance

First-principles definition of ionicity and covalency in molecules and solids.

The notions of ionicity and covalency of chemical bonds, effective atomic charges, and decomposition of the cohesive energy into ionic and covalent terms are fundamental yet elusive. For example, different approaches give different values of atomic charges. Pursuing the goal of formulating a universal approach based on firm physical grounds (first-principles or non-empirical), we develop a formalism based on Wannier functions with atomic orbital symmetry and capable of defining these notions and giving numerically robust results that are in excellent agreement with traditional chemical thinking. Unexpectedly, in diamond-like boron phosphide (BP), we find charges of +0.68 on phosphorus and -0.68 on boron atoms, and this anomaly is explained by the Zintl-Klemm nature of this compound. We present a simple model that includes energies of the highest occupied cationic and lowest unoccupied anionic atomic orbitals, coordination numbers, and strength of interatomic orbital overlap. This model captures the essential physics of bonding and accurately reproduces all our results, including anomalous BP.

Structural, Electromagnetic and Thermodynamic Analysis of Ion Pollutants Adsorption in Water by Gallium Nitride Nanomaterial: a Green Chemistry Application

Gallium nitride (Ga–N) nanocage can effectively remove alkali and alkaline earth metal ions from water. Therefore, it has been found a selective competition for metal cations in the Ga–N. The electronic, magnetic and thermodynamic properties of alkali-alkaline earth metal ion-adsorbed Ga–N have been investigated using density functional theory. The results denote that alkali/alkaline earth-metal ion-adsorbed Ga–N systems are stable compounds, with the most stable adsorption site being the center of the cage ring. In addition, because of charge transfer from Ga–N to the alkali/alkaline earth-metal cations show clear n-type adsorbing behavior. The absorption of alkali metal atoms on alkali/alkaline earth-metal cations occur via chemisorption. In this article, the behavior of trapping of main group cations of Li+, Na+, K+, Be2+, Mg+ and Ca2+ by gallium nitride nanocone was observed for sensing the water metal cations. The essence of covalent traits for these clusters has displayed the similar energy value and image of the PDOS for the p states of N, the d states of Ga and s orbitals of metal cations including Li+, Na+, K+/Be2+, Mg2+ and Ca2+ through water treatment. The partial density of states (PDOS) can also estimate a certain charge assembly between Li+, Na+, K+/Be2+, Mg2+ and Ca2+ and Ga–N which indicate the complex dominant of metallic features and an exact degree of covalent traits between alkali/alkaline earth-metal cations and gallium nitride nanocage. Furthermore, the NMR spectroscopy has indicated the remarkable peaks around metal elements of Li+, Na+, K+, Be2+, Mg+ and Ca2+ through the trapping in the Ga–N during ion detection and removal from water; however, there are some fluctuations in the chemical shielding behaviors of isotropic and anisotropy attributes. In addition, all accounted \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta G_{R}^{o}$$\\end{document} amounts are very close, which demonstrate the agreement of the measured specifications by all methodologies and the reliability of the computing values.

Asymmetric response of transition metal cationic orbitals to applied electric field

Understanding the quantum mechanical mechanisms underlying atomic/ionic interfacial processes and phenomena, particularly their dependence on the electronic orbital rearrangement of atoms/ions in an external electric field, remains a significant challenge. This study investigated the asymmetric response of transition metal (TM) cationic orbitals when subjected to an applied electric field. Quantum mechanical calculations were employed to quantify the newly formed hybrid orbitals and evaluate the corresponding orbital energies of the TM cations. Analysis of the quantitative contribution of asymmetric orbital hybridization to TM–surface interactions showed a significant change in orbital energy and increased effective charges of TM cations at the charged surface. This asymmetric response, induced by a negative external electric field generated from the structural charges of clay minerals (e.g., montmorillonite), repels electrons from the outer-shell orbital. This repulsion consequently increases the electron binding energy of the inner-shell orbitals, leading to new surface reactions, polarization-enhanced induction force, and polarization-induced covalent bonding between the TM cations and the charged surface. Our theoretical predictions regarding TM–clay mineral interactions are consistent with the experimental observations of TM cation adsorption. This finding has significant implications for the adsorptive removal of TM cations from wastewaters and for enhancing the catalytic efficiency of TM–surface catalysts. The unique physical and chemical characteristics exhibited by TMs at charged particle surfaces, resulting from their asymmetric response, can play pivotal roles in environmental and chemical engineering.

Fluorination and Conjugation Engineering Synergistically Enhance the Optoelectronic Properties of Two-Dimensional Hybrid Organic-Inorganic Perovskites.

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) are expected to be a viable alternative to three-dimensional (3D) analogs in solar cells (SCs) and optoelectronic devices due to their high stability, diverse composition, and physical properties. However, unsuitable band alignment and large bandgaps limit the power conversion efficiency (PCE) improvement of SCs based on 2D HOIPs. Here, we report a molecular design strategy that combines fluorination and conjugation engineering to tune the electronic structure and optimize the PCE of 2D HOIPs. Our results show that type IIa band alignment and tunable bandgaps can be achieved in 2D Dion-Jacobson (DJ) HOIPs by H/F substitution of organic cations with different degrees of conjugation. In general, the bandgap of 2D DJ-HOIPs decreases monotonously with the increase of the number of F atoms, which is due to the gradual decrease of the lowest unoccupied molecular orbitals (LUMO) of organic cations. In addition, the enhanced interlayer charge transfer and higher dielectric constant suggest that the fluorination-induced dielectric limitations are weakened. The estimated PCE of 2D DJ-HOIPs is exponentially increased and positively correlated with the degree of conjugation and fluorination of organic cations, with a PCE approaching 29% under their synergistic effect. Our results not only provide promising candidates for photovoltaic device applications but also provide an effective method for PCE optimization.

Signatures of superconductivity near 80 K in a nickelate under high pressure.

Although high-transition-temperature (high-Tc) superconductivity in cuprates has been known for more than three decades, the underlying mechanism remains unknown1-4. Cuprates are the only unconventional superconductors that exhibit bulk superconductivity with Tc above the liquid-nitrogen boiling temperature of 77 K. Here we observe that high-pressure resistance and mutual inductive magnetic susceptibility measurements showed signatures of superconductivity in single crystals of La3Ni2O7 with maximum Tc of 80 K at pressures between 14.0 GPa and 43.5 GPa. The superconducting phase under high pressure has an orthorhombic structure of Fmmm space group with the [Formula: see text] and [Formula: see text] orbitals of Ni cations strongly mixing with oxygen 2p orbitals. Our density functional theory calculations indicate that the superconductivity emerges coincidently with the metallization of the σ-bonding bands under the Fermi level, consisting of the [Formula: see text] orbitals with the apical oxygen ions connecting the Ni-O bilayers. Thus, our discoveries provide not only important clues for the high-Tc superconductivity in this Ruddlesden-Popper double-layered perovskite nickelates but also a previously unknown family of compounds to investigate the high-Tc superconductivity mechanism.

Formation of CuIn(1-x)GaxS2 Thin Films through a Solution Approach: Nonlinear Variation of Fermi Energy and Band Gap Bowing.

We report the formation of CuIn(1-x)GaxS2 (CIGS) thin films through a solution approach, namely, successive ionic layer adsorption and reaction (SILAR) technique. The obtained films possessed a high degree of crystallinity indicating the efficacy of the deposition process in forming CIGS films. A series of alloys have evidenced band gap bowing, that is, the optical band gap does not follow a linear relationship with the composition; the band gap of an intermediate compound is higher than that is interpolated from a linear relationship or Vegard's law. The composition-dependent band gap followed a quadratic relationship evidencing reverse band gap bowing, manifesting an upward convex behavior. With scanning tunneling spectroscopy (STS) and thereby the density of states of the disordered semiconductors, we have observed a bowing behavior in the transport gap as well and identified the roles of the conduction and valence bands in yielding the bowing phenomenon. The results are explained in terms of the anionic and cationic orbitals involved in forming the two bands. The STS studies have been analyzed further to derive the Urbach energy of the disordered semiconductors. When STS studies are combined with Kelvin probe force microscopy, which in effect provides the Fermi energy of the alloyed semiconductors, we could derive the band edges and the Fermi energy of the whole series in an absolute energy scale during the manifestation of the bowing phenomenon.

Quasi‐1D Antiferroelectricity in Centrosymmetric CsTaS3 Crystal

Abstract1D ferroelectric (FE) materials are expected to be promising low‐dimensional materials for nanometer devices, but are rarely reported. The previous experiment discovered that quasi‐1D CsTaS3 crystalizes in centrosymmetric space group, but in which the Ta cations have a strange shift along the c axis from the center of TaS6 octahedron. Here, the crystal structure, electronic structure, ferroelectric, and piezoelectric properties of CsTaS3 by using first‐principles calculations are studied. It is found that the empty d orbitals of Ta cations induce the distortions of TaS6 octahedra, which bring the polarity along a given [TaS3]− chain. The adjacent chains are antiferroelectric (AFE) coupling making CsTaS3 being an AFE material. However, the FE phase of CsTaS3 is supposed to be accessible since its total energy is only 0.3 meV per formula higher than that of the AFE phase. The polarization of FE CsTaS3 is estimated to be 16.8 μC cm−2, which is comparable to those of well‐known FE perovskites. The work predicts a quasi‐1D AFE material, which would be helpful for subsequent experimental work.

Tuning valley degeneracy with band inversion

Valley degeneracy in materials with inverted bands can be increased by strengthening the band inversion. One method to tune the band inversion is by controlling the chemical interactions between cation and anion atomic orbitals.

Highly Robust {Ln4}-Organic Frameworks (Ln = Ho, Yb) for Excellent Catalytic Performance on Cycloaddition Reaction of Epoxides with CO2 and Knoevenagel Condensation

Due to the high electron charge, large ion radius, and plentiful outer hybrid orbitals of LnIII cations, microporous Ln-MOFs can be used as Lewis acidic catalysts with high catalytic activity for a variety of organic reactions, which prompts us to explore cluster-based nanoporous Ln-MOFs by employing structure-oriented ligands. Herein, the exquisite combination of coplanar [Ln4(μ3–OH)2(μ2–HCO2)(H2O)2] clusters (abbreviated as {Ln4}) and the structure-oriented multifunctional ligand of 2,6-bis(2,4- dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H5BDCP) led to two isomorphic nanoporous frameworks of {(Me2NH2)[Yb4(BDCP)2(μ3–OH)2(μ2–HCO2)(H2O)2]·5DMF·H2O}n (NUC-38Yb) and {(Me2NH2)[Ho4(BDCP)2(μ3–OH)2(μ2– HCO2)(H2O)2]·6DMF·3H2O}n (NUC-38Ho). To the best of our knowledge, NUC-38Ho and NUC-38Yb are rarely reported {Ln4}-based three-dimensional (3D) frameworks with embedded hierarchical triangular-microporous and hexagonal-nanoporous channels, which are shaped by six rows of coplanar {Ln4} clusters and characterized by plentiful coexisting Lewis acid–base sites on the inner wall including open LnIII sites, Npyridine atoms, μ3–OH, and μ2–HCO2. Catalytic experiments performed using NUC-38Yb as the representative exhibited that NUC-38Yb possessed a high catalytic activity on the cycloaddition reactions of epoxides with CO2 under mild conditions, which can be ascribed to its structural advantages including nanoscale channels, rich bifunctional active sites, large surface areas, and chemical stability. Moreover, NUC-38Yb, as a heterogeneous catalyst, could greatly accelerate the Knoevenagel condensation reactions of aldehydes and malononitrile. Hence, this work paves the way for the construction of functional Ln-cluster-based nanoporous metal–organic frameworks (MOFs) by elaborately designing functional ligands with transnormal connection modes.

Engineering metal-sulfides with cations-tunable metal-oxides electrocatalysts with promoted catalytic conversion for robust ions-storage capability

Metal rich-sulfides, with remarkable theoretical capacity, still suffer from the disolving of polysulfides and sluggish kinetics. Electrocatalysts, as the vital meditors, have been applied in Li-S systems with notable improvements, but scarcely explored for ions-storage battery. Herein, for introducting cation-tunable MOx (M=Mn/Fe/Co/Ni) as electrocatalysts, various MoS2@MOx are designed through chemical-precipitation and thermal-treatment manners. Benefitting from the high affinity of MoS2 and MOx, the interfacial chemical bonds Mo-S-M are established, boosting the improvement of ions/electrons transferring and structural integrality. Owing to the evolution of outer orbitals and ionic radius, the capturing and conversion of Li2S8 are tailored in order of Fe2O3>MnO>CoO>NiO. Supported by unique 3d-orbital/ion-radiu and Mo-S-Fe bonds, the ultra-fast ability of MoS2@Fe2O3 remains ∼612 mAh g−1 after 3,000 loops even at 5.0 A g−1, meanwhile delivering ∼800 mAh g−1 at 0.5 A g−1 in full-cell. Assisted by detailed kinetic behaviors and theoretical calculations, the redox reaction mechisms are clearly proposed, whilst the reduced Gibbs free energy (-1.25 of Fe2O3) serves crucial roles in the reaction (Li2S8 → Li2S6). This work is expected to shed light on the in-depth understanding of fourth-periods MOx electrocatalysts, and offers more possibilities for designing advanced metal-sulfides electrodes.MoS2 nanosheets uniformly anchored with MOx (M=Mn, Fe, Co, Ni) were rationally engineered, accompanied by the establishment of Mo-S-M interfacial chemical bonds. The electrocatalytic abilities of introduced MOx were successfully tailored by the evolution of cationic outer orbitals and ionic radius, inducing the fascinated catalytic conversion behaviors.

Interfacial charge transfer mechanism of oxygen reduction reaction in alkali media: Effects of molecular charge states and triphenylamine substituent on cobalt porphyrin electrocatalysts

Substituents can affect the partial charge distribution on porphyrin, and in tandem with the ion states in electrolyte, the charge transfer mechanism can be altered at catalytic interface. Three cobalt porphyrins with methyl phenyl, 2,1,3-benzothiadiazole (BTD) and BTD-triphenylamine (TPA) substituents at the 5,15-positions, nominated as CoPor, BTD-CoPor and TPA-BTD-CoPor, respectively, have been examined in oxygen reduction reactions (ORR) under alkaline condition. Reduced reduction potentials and enhanced response current densities were observed on the two substituent porphyrin-coated catalysts as compared to CoPor/C. Importantly, TPA-BTD-CoPor/C obtained slightly larger ORR current with less hydroperoxide anion generation yields than BTD-CoPor/C. We proposed that the electronic structure along with the induced partial charge effect caused the difference in ORR potential, while the electron-withdrawing property of BTD contributed to the increased response current. Though TPA unit still benefits the ORR performance, the more exposed cation orbitals on TPA that merit the acidic ORR activity was suggested to be ineffective in alkali condition. These findings demonstrate the importance of the induced intramolecular partial charges in affecting the catalytic process in alkali medium and point out the limitation in utilizing the structural merit of TPA in accelerating the interfacial charge transfer.

Substituents and the induced partial charge effects on cobalt porphyrins catalytic oxygen reduction reactions in acidic medium

Charge states at the catalytic interface can intensely alter the charge transfer mechanism and thus the oxygen reduction performance. Two symmetric cobalt porphyrins with electron deficient 2,1,3-benzothiadiazole (BTD) and electron-donating propeller-like triphenylamine (TPA) derivatives have been designed firstly, to rationally generate intramolecular partial charges, and secondly, to utilize the more exposed molecular orbitals on TPA for enhancing the charge transfer kinetics. The catalytic performance of the two electrocatalysts was examined for oxygen reduction reactions (ORR) in acidic electrolyte. It was found that BCP1/C with two BTD groups showed greater reduction potential but less limiting current density as compared to BCP2/C bearing BTD-TPA units. The reduced potential of BCP2/C was proposed to the introduction of the electron-donating ability of TPA, which may decrease the adsorption affinity of oxygen to the cobalt center. Both dipole-induced partial charge effect and the more exposed cation orbitals of the 3D structural TPA were proposed to contribute to the increased response current of BCP2/C. In addition, BCP2/C attained more than 80% of H2O2 generation in acidic solution, which may also relate to the structural effect. These findings may provide new insight into the structural design of organic electrocatalysts and deep understanding on the interfacial charge transfer mechanism for ORR.

Hole antidoping of oxides

In standard doping, adding charge carrier to a compound results in a shift of the Fermi level towards the conduction band for electron doping and towards the valence band for hole doping. We discuss the curious case of antidoping, where the direction of band movements in response to doping is reversed. Specifically, $p$-type antidoping moves the previously occupied bands to the principal conduction band resulting in an increase of band gap energy and reduction of electronic conductivity. We find that this is a generic behavior for a class of materials: early transition and rare-earth metal (e.g., Ti, Ce) oxides where the sum of composition-weighed formal oxidation states is positive; such compounds tend to form the well-known electron-trapped intermediate bands localized on the reduced cation orbitals. What is less known is that doping by a hole annihilates a single trapped electron on a cation. The latter thus becomes electronically inequivalent with respect to the normal cation in the undoped lattice, thus representing a symmetry-breaking effect. We give specific theoretical predictions for target compounds where hole antidoping might be observed experimentally: Magn\'eli-like phases (i.e., $\mathrm{Ce}{\mathrm{O}}_{2\text{\ensuremath{-}}x}$ and $\mathrm{Ti}{\mathrm{O}}_{2\text{\ensuremath{-}}x}$) and ternary compounds (i.e., $\mathrm{B}{\mathrm{a}}_{2}\mathrm{T}{\mathrm{i}}_{6}{\mathrm{O}}_{13}$ and $\mathrm{B}{\mathrm{a}}_{4}\mathrm{T}{\mathrm{i}}_{12}{\mathrm{O}}_{27}$), and note that this unique behavior opens the possibility of unconventional control of materials conductivity by doping.

Theoretical Study of the Band-gap Differences among Lead Triiodide Perovskite Materials: CsPbI3, MAPbI3, and FAPbI3

We present a theoretical analysis for the band-gap difference among the cubic lead triiodide perovskite materials by using a NH4+ probe molecule. We show the position of A-site cation induces the removal of 3-fold degeneracy of Pb(6px, 6py, 6pz), which are the main part of the conduction band minimum (CBM). The degree of stabilization of CBM depends on the overlap integrals between occupied molecular orbitals of A-site cation and unoccupied 6p orbitals of Pb.

The effects of charge density distributions of metal ions on single water molecule dissociation of [M(H2O)6]3+ systems

Some effects of cationic charge density distribution on single water molecule dissociation of [M(H2O)6]3+ clusters with M=Cr, Mn, Fe, Co, and Ni have been investigated using first-principles study. The molecular structures, molecular binding energies, hydration enthalpies, cation and water molecules orbitals, infrared vibrational frequencies, and potential energy surfaces/curves had been computed to fulfill the purpose of research. Our investigation results have revealed that the hollow shape of charge density of central Cr(III) makes the Cr-O bonds rigid as indicated by a higher activation energy for releasing one water molecule from [Cr(H2O)6]3+. The isotropic charge density of Fe(III) affects in lowering water rotational rigidities which is responsible for augmenting the activation energy, while the cones-shape charge density of Ni(III) weakens the ion-dipole interactions by increasing interactions between nearest neighbour water molecules.

Origin of High Mobility in InSnZnO MOSFETs

The origins of higher mobility characteristics of In-Sn-Zn-O (InSnZnO) MOSFETs than those of conventional In-Ga-Zn-O (InGaZnO) MOSFETs were investigated. Comprehensive analyses of temperature and surface carrier concentration ( ${N} _{s}$ ) dependence of mobility revealed the aspects of potential profile around mobility edge ( ${E} _{c}$ ) in InSnZnO MOSFET. Incorporated Sn atoms were found to increase the potential fluctuation around ${E} _{c}$ at low ${N} _{s}$ compared to conventional InGaZnO MOSFET, but enhance the overlapping of electron orbitals of cations with In atoms, which results in mobility improvement by band transport.

Invariant wide bandgaps in honeycomb monolayer and single-walled nanotubes of IIB–VI semiconductors

The search for low-dimensional materials with unique electronic properties is important for the development of electronic devices in the nanoscale. Through systematic first-principles calculations, we found that the band gaps of the two-dimensional honeycomb monolayers (HMs) and one-dimensional single-walled nanotubes (SWNTs) of IIB–VI semiconductors (ZnO, CdO, ZnS and CdS) are nearly chirality-independent and weakly diameter-dependent. Based on analysis of the electronic structures, it was found that the conduction band minimum is contributed to by the spherically symmetric s orbitals of cations and the valence band maximum is dominated by the in-plane and hybridizations. These electronic states are robust against radius curvature, resulting in the invariant feature of the band gaps for the structures changing from HM to SWNTs. The band gaps of these materials range from 2.3 to 4.7 eV, which is of potential application in electronic devices and optoelectronic devices. Our studies show that searching for and designing specific electronic structures can facilitate the process of exploring novel nanomaterials for future applications.

(Invited) Discovering Wide Band Gap Oxide Semiconductors By Engineering Strong Electron Correlations

Wide gap semiconductors are often designed based on energy separation of the cation and oxygen orbitals. In strongly correlated semiconductors, however interacting electrons create effective transport gaps based on the occupancy of orbitals. I will discuss some recent examples from our laboratory on discovery of new electronic phases that have gaps of the order of 3eV that have been designed by electron doping of perovskite nickelates. In the un-doped case, these systems possess small gaps of the order of 0.1eV, and adding electrons to the partially filled d-orbitals, enhances the gap to 3eV taking advantage of strong correlations in the eg orbitals of Ni sites. This new strategy allows us to create wide gaps in semiconductors that are nominally metallic or nearly-metallic like in the pristine state and could be expanded to a broader range of materials systems. Besides the gap opening that in itself is fascinating, there are several opportunities to tune these materials to achieve multiple resistance states, continuous tuning of resistance by anion-site disorder and create multi-functionality. I will then give some examples of their applications in neural science and engineering, photonics and evolutionary biology.

On the Attosecond charge migration in Cl…..N, Cl…..O, Br…..N and Br…..O Halogen-bonded clusters: Effect of donor, acceptor, vibration, rotation, and electron correlation

The electron-electron relaxation and correlation-driven charge migration process, which features pure electronic aspect of ultrafast charge migration phenomenon, occurs on a very short timescale in ionized molecules and molecular clusters, prior to the onset of nuclear motion. In this article, we have presented nature of ultrafast pure electronic charge migration dynamics through Cl…..N, Cl…..O, Br…..N, and Br…..O halogen bonds, explored using density functional theory. We have explored the role of donor, acceptor, electron correlation, vibration and rotation in charge migration dynamics through these halogen bonds. For this work, we have selected ClF, Cl2, ClOH, ClCN, BrF, BrCl, BrOH, and BrCN molecules paired with either NH3 or H2O. We have found that the timescale for pure electron-electron relaxation and correlation-driven charge migration through the Cl…..N, Br…..N, Cl…..O, and Br…..O halogen bonds falls in the range of 300–600 attosecond. The primary driving force behind the attosecond charge migration through the Cl…..N, Br…..N, Cl…..O, and Br…..O halogen bonds is the energy difference (ΔE) between two stationary cationic orbitals (LUMO- β and HOMO- β), which together represents the initial hole density immediately following vertical ionization. We have also predicted that the strength of electron correlation has significant effect on the charge migration timescale in Cl…..N, Br…..N, Cl…..O, and Br…..O halogen bonded clusters. Vibration and rotation are also found to exhibit profound effect on attosecond charge migration dynamics through halogen bonds. The attosecond charge migration dynamics through Cl…..N, Cl…..O, Br…..N, and Br…..O halogen bonds depends on strength of electron correlation, donor and acceptor, the energy difference (ΔE) between two stationary cationic orbitals (LUMO-β and HOMO-β) involved in electronic superposition, vibration and rotation.