Re-delocalization of localized d-electrons in VO_(2)(R)-VS_(4)hetero-structure enables high performance of rechargeable Mg-ion batteries

Rechargeable Mg-ion batteries(MIBs)have attracted much more attentions by virtue of the high capacity from the two electrons chemistry.However,the reversible Mg^(2+)diffusion in cathode materials is restricted by the strong interactions between the high-polarized bivalent Mg^(2+)ions and anionic lattice.Herein,we design and propose a hetero-structural VO_(2)(R)-VS_(4)cathode,in which the re-delocalized d-electrons can effectively shield the polarity of Mg^(2+)ions.Theoretically,the electrons should spontaneously transfer from VS_(4)to VO_(2)(R)through the interfaces of hetero-structure due to the lower work function value of VS_(4).Furthermore,the internal electrons transfer lead to the electronic injection into VO_(2)(R)from VS_(4)and the partially broken V-V dimers,indicating the presence of lone pair electrons and charge re-delocalization.Benefiting from the shield effect of re-delocalized electrons,and the weakened attraction between cations and O/S anions enables more S^(2-)-S_(2)^(2-)redox groups to participate the electrochemical reactions and compensate the double charge of Mg^(2+)ions.Accordingly,VO_(2)(R)-VS_(4)hetero-structure exhibits a high specific capacity of 554 mA h g^(-1)at 50 mA g^(-1).It is believed that the charge re-delocalization of cathode extremely boost the Mg^(2+)ions migration for the high-capacity of MIBs.

Inducing Fe 3d Electron Delocalization and Spin‑State Transition of FeN_(4) Species Boosts Oxygen Reduction Reaction for Wearable Zinc–Air Battery

Transition metal-nitrogen-carbon materials(M-N-Cs),particularly Fe-N-Cs,have been found to be electroactive for accelerating oxygen reduction reaction(ORR)kinetics.Although substantial efforts have been devoted to design Fe-N-Cs with increased active species content,surface area,and electronic conductivity,their performance is still far from satisfactory.Hitherto,there is limited research about regulation on the electronic spin states of Fe centers for Fe-N-Cs electrocatalysts to improve their catalytic performance.Here,we introduce Ti_(3)C_(2) MXene with sulfur terminals to regulate the electronic configuration of FeN_(4) species and dramatically enhance catalytic activity toward ORR.The MXene with sulfur terminals induce the spin-state transition of FeN_(4) species and Fe 3d electron delocalization with d band center upshift,enabling the Fe(II)ions to bind oxygen in the end-on adsorption mode favorable to initiate the reduction of oxygen and boosting oxygen-containing groups adsorption on FeN_(4) species and ORR kinetics.The resulting FeN_(4)-Ti_(3)C_(2)Sx exhibits comparable catalytic performance to those of commercial Pt-C.The developed wearable ZABs using FeN_(4)-Ti_(3)C_(2)Sx also exhibit fast kinetics and excellent stability.This study confirms that regulation of the electronic structure of active species via coupling with their support can be a major contributor to enhance their catalytic activity.

Enhanced charge separation by interchain hole delocalization in nonfullerene acceptor-based bulk heterojunction materials

Bulk heterojunction(BHJ)composites show improved power conversion efficiencies when optimized in terms of morphology using various film processing methods.A reduced carrier recombination loss in an optimized BHJ was characterized previously.However,the driving force that leads to this reduction was not clearly understood.In this study,we focus on the decreased carrier recombination loss and its driving force in optimized nonfullerene acceptor-based PTB7-Th:IEICO-4F BHJ composites.We demonstrate that the optimized BHJ shows deactivation in the sub-nanosecond nongeminate carrier recombination process.The driving force for this deactivation was determined to be the improved interchain hole delocalization between the polymers.An enhanced interchain hole delocalization was observed using steady-state photoinduced absorption(PIA)spectroscopy.In particular,increased splitting between the polaron PIA bands was noted.Moreover,improved interchain hole delocalization was observed for other state-of-the-art BHJ materials,including D18:Y6 with optimized morphologies.

Localization and delocalization of a one-dimensional system coupled with the environment

We investigate several models of a one-dimensional chain coupling with surrounding atoms to elucidate disorder- induced delocalization in quantum wires, a peculiar behaviour against common wisdom. We show that the localization length is enhanced by disorder of side sites in the case of strong disorder, but in the case of weak disorder there is a plateau in this dependence. The above behaviour is the conjunct influence of the coupling to the surrounding atoms and the antiresonant effect. We also discuss different effects and their physical origin of different types of disorder in such systems. The numerical results show that coupling with the surrounding atoms can induce either the localization or delocalization effect depending on the values of parameters.

Intraparticle Charge Delocalization through Conjugated Metal-Ligand Interfacial Bonds:Effects of Metal d Electrons

Intraparticle charge delocalization occurs when metal nanoparticles are functionalized with organic capping ligands through conjugated rnetal-ligand interfacial bonds. In this study, metal nanoparticles of 5d metals （Ir, Pt, and Au） and 4d metals （Ru, Rh, and Pd） were prepared and capped with ethynylphenylacetylene and the impacts of the number of metal d electrons on the nanoparticle optoelectronic properties were examined. Both FTIR and photoluminescence measurements indicate that intraparticle charge delocalization was en- hanced with the increase of the number of d electrons in the same period with palladium being an exception.

Electron delocalization enhances the thermoelectric performance of misfit layer compound(Sn_(1-x)Bi_(x)S)_(1.2)(TiS_(2))_(2)

The misfit layer compound(SnS)_(1.2)(TiS_(2))_(2)is a promising low-cost thermoelectric material because of its low thermal conductivity derived from the superlattice-like structure.However,the strong covalent bonds within each constituent layer highly localize the electrons thereby it is highly challenging to optimize the power factor by doping or alloying.Here,we show that Bi doping at the Sn site markedly breaks the covalent bonds networks and highly delocalizes the electrons.This results in a high charge carrier concentration and enhanced power factor throughout the whole temperature range.It is highly remarkable that Bi doping also significantly reduces the thermal conductivity by suppressing the heat conduction carried by phonons,indicating that it independently modulates phonon and charge transport properties.These effects collectively give rise to a maximum ZT of 0.3 at 720 K.In addition,we apply the single Kane band model and the Debye–Callaway model to clarify the electron and phonon transport mechanisms in the misfit layer compound(SnS)_(1.2)(TiS_(2))_(2).

THE SPIN DELOCALIZATION SUBSTITUENT PARAMETER σ 10. SYNTHESIS OF SUBSTITUTED α, β, β-TRIFLUOROSTYRENES BY THE Pd-CATALYZED CROSS-COUPLING OF TRIFLUOROVINYLZINC BROMIDE WITH ARYL HALIDES

Palladium-catalyzed coupling of trifluorovinylzinc reagent with substituted aryl halides Y-C_6H_4-X (Y=p-NO_2, p-and m-COOMe, p-COOH, p-CONH_2, p- and m-CN; X=Br, I, Cl) provides a synthetic method for α, β, β-trifluorostyrenes(Y-TFS's). A series of previously unavailable Y-TFS's were thus obtained.

Entanglement-Enhanced Two-Photon Delocalization in a Coupled-Cavity Array

We study the transport properties of two entangled photons which are initially injected into two nearest-neighbor coupling cavities in an one-dimensional coupled-cavity array （CCA）. It is found that photonic transport dynamics in the two-photon CCA exhibits the entanglement-enhanced two-photon delocalization phenomenon. It is shown that the CCA can realize the localization-to-delocalization transition for two entangled photons.

Localization−delocalization transitions in non-Hermitian Aharonov−Bohm cages

A unique feature of non-Hermitian systems is the extreme sensitivity of the eigenspectrum to boundary conditions with the emergence of the non-Hermitian skin effect (NHSE). A NHSE originates from the point-gap topology of complex eigenspectrum, where an extensive number of eigenstates are anomalously localized at the boundary driven by nonreciprocal dissipation. Two different approaches to create localization are disorder and flat-band spectrum, and their interplay can lead to the anomalous inverse Anderson localization, where the Bernoulli anti-symmetric disorder induces mobility in a full-flat band system in the presence of Aharonov−Bohm (AB) Cage. In this work, we study the localization−delocalization transitions due to the interplay of the point-gap topology, flat band and correlated disorder in the one-dimensional rhombic lattice, where both its Hermitian and non-Hermitian structures show AB cage in the presence of magnetic flux. Although it remains the coexistence of localization and delocalization for the Hermitian rhombic lattice in the presence of the random anti-symmetric disorder, it surprisingly becomes complete delocalization, accompanied by the emergence of NHSE. To further study the effects from the Bernoulli anti-symmetric disorder, we found the similar NHSE due to the interplay of the point-gap topology, correlated disorder and flat bands. Our anomalous localization−delocalization property can be experimentally tested in the classical physical platform, such as electrical circuit.

Electron delocalization-enhanced sulfur reduction kinetics on an MXene-derived heterostructured electrocatalyst

Lithium-sulfur(Li-S)batteries mainly rely on the reversible electrochemical reaction of between lithium ions(Li^(+))and sulfur species to achieve energy storage and conversion,therefore,increasing the number of free Li^(+)and improving the Li^(+)diffusion kinetics will effectively enhance the cell performance.Here,Mo-based MXene heterostructure(MoS_(2)@Mo_(2)C)was developed by partial vulcanization of Mo_(2)C MXene,in which the introduction of similar valence S into Mo-based MXene(Mo_(2)C)can create an electron delocalization effect.Through theoretical simulations and electrochemical characterisation,it is demonstrated that the MoS_(2)@Mo_(2)C heterojunction can effectively promote ion desolvation,increase the amount of free Li^(+),and accelerate Li^(+)transport for more efficient polysulfide conversion.In addition,the MoS_(2)@Mo_(2)C material is also capable of accelerating the oxidation and reduction of polysulfides through its sufficient defects and vacancies to further enhance the catalytic efficiency.Consequently,the Li-S battery with the designed MoS_(2)@Mo_(2)C electrocatalyst performed for 500 cycles at 1 C and still maintained the ideal capacity(664.7 mAh·g^(−1)),and excellent rate performance(567.6 mAh·g^(−1)at 5 C).Under the extreme conditions of high loading,the cell maintained an excellent capacity of 775.6 mAh·g^(−1)after 100 cycles.It also retained 838.4 mAh·g^(−1)for 70 cycles at a low temperature of 0℃,and demonstrated a low decay rate(0.063%).These results indicate that the delocalized electrons effectively accelerate the catalytic conversion of lithium polysulfide,which is more practical for enhancing the behaviour of Li-S batteries.

Electronic structure and ultraviolet spectra of p-C_(6)H_(4)-C_(20)

Geometry optimization of p-C_(6)H_(4)-connected cyclo[20]carbon(p-C_(6)H_(4)-C_(20))was carried out at M062X/6-311G(d,p)level,three kinds of bond orders(Mayer,Laplacian,and Wiberg),electron-hole distributions,localized orbital locators(LOL),and infrared(IR)spectrum were also performed at the same level.Based on TD-DFT M062X/6-311G(d,p)method,the first 20 excited states and ultraviolet(UV)spectra of p-C_(6)H_(4)-C_(20) were calculated.Calculation results of π-electron delocalization analyses prove thatπ-electron delocalization of p-C_(6)H_(4)-C_(20) is more likely to occur on shorter C-C bonds rather than longer C-C bonds,and inside/outside of the ring plane rather than above/below the ring plane.Two absorption peaks of p-C_(6)H_(4)-C_(20) locate at about 319 nm and 236 nm,respectively.

Increasing high-temperature fatigue resistance of polysynthetic twinned TiAl single crystal by plastic strain delocalization

Polysynthetic twinned(PST)TiAl single crystal possesses great potentials for high-temperature applications due to its excellent combination of strength,ductility and creep resistance.However,a critical property for high-temperature application of such material involving high-temperature fatigue properties remains unknown.Here,the high-temperature high-cycle fatigue performance of PST TiAl single crystal has been studied.The result shows that PST TiAl single crystal can withstand more than 107 cyclic loadings at 975℃ under a stress amplitude of 270 MPa,which is significantly higher than traditional TiAl alloys.Experimental observations and atomistic simulations indicate that the improvement of fatigue resistance is attributed to the plastic strain delocalization in uniform lamellar structure,and the plastic deformation is well-distributed and sufficient in each lamella.Even in theα2 lamella with difficult slippage,a large number of stacking fault structures can be observed.The{c+a}dislocations inα2 tend to dissociate into a Frank partial with b=1/6<2^(-)20^(-)3>,forming a ribbon of I1 fault which ensures the continuity of deformation.

Quark Delocalization,Color Screening and Nuclear Intermediate Range Attraction——The Center of Mass Motion Effect

In our first Paper,we proposed a new QCD model to deal with hadron interaction.The key ingredients of this model are quark delocalization and color screening.The quarkdelocalizafion is modelled from electron delocalization in molecular physics and the colorscreening is inspirited by the lattice QCD calculations.In this way we obtained the nu-clear intermediate range attraction and the qualitative fit of N—N phase shifts.Following the quark potential model,the quark wave function of a single baryon ischosen to be a Gaussian

Localization and delocalization of light in photonic moiré lattices

With the support by the National Natural Science Foundation of China,the research team led by Ye FangWei(叶芳伟)at the Shanghai Jiao Tong University(SJTU),with collaborations from other researchers,created the first photonic moirélattices,demonstrated the light localization in moirélattices,and revealed a new mechanism for wave localization:moirélattice-based flat band.The finding was published in Nature(2020,577:42—46).

The spin delocalization substituent parameter σ——8. The spin-delocalizing abilities of the nitro, cyano, carbomethoxy, carboxy and carbamyl groups

The rate constants (k) of the homo-cycloaddition reactions of five substituted α, β, β-tri- fluorostyrenes (TFS’s), i.e. p-nitrotrifluorostyrene (4), p-cyanotrifluorostyrene (5), p-carbomethoxytri- fluorostyrene (6), p-carboxytrifluorostyrene (7) and p-carbamyltrifluorostyrene (8), have been measured in the temperature range of 110-160℃. The ~σmb polar substituent parameters of these TFS's cal- culated from ^(19) F NMR chemical shifts are: NO_2, 0.86; CN, 0.86; CO_2CH_2, 0.40; CO_2H, 0.31; CONH_2, 0.10. The spin delocalization substituent parameters ~σT of NO_2, CN, CO_2 CH_2, CO_2H and CONH_2 are 0.32, 0.38, 0.31, 0.37 and 0.37 respectively. Thus all these electron-pair attracting groups are also very effective spin-stabilizers.

The spin delocalization substituent parameter σ(?)——6.The spin-delocalizing abilities of the thiomethyl,cyclopropyl and t-butyl groups.Synthesis of three substituted trifluorostyrenes

Three substituted α,β,β-trifluorostyrenes(TFS's),i.e.,p-thiomethyltrifluorostyrene(4), p-cyclopropyltrifluorostyrene(5)and p-t-butyltrifluorostyrene(6),have been synthesized.The rate constants(k_2)of the thermal cyclodimerization of these compounds have been measured in the tem- perature range 120—160℃.The polar parameters σ_(mb) of these TFS's calculated from ^(19)F NMR chemi- cal shifts are:for p-thiomethyl,-0.18;p-cyclopropyl,-0.31 and p-t-butyl,-0.22.The spin delo- calization substituent parameters σ'_T(140°)of p-thiomethyl,cyclopropyl and t-butyl groups are 0.59, 0.27 and 0.30 respectively.Thus all of these groups act as electron-donating groups which can also effectively stabilize a spin.

Mesons in the Constituent Quark Model

The quark-antiquark （q^-q） spectrum is studied by solving the Schrōdinger equation in the framework of nonrelativistic constituent quark model. An overall good fit to the experimental data of meson is obtained. The interactions between quark and antiquark consist of quadratic colour confinement-exchange, one-gluon-exchange, and Goldstone-boson-exchange potentials.

Localization Exponent for the Second Landau Level in the Quantum Hall Effect

At temperature above 1 K, we measured the temperature dependence of the longitudinal and Hall resistivity ρxx,ρxy in the regime of the quantum Hall plateau-to-plateau transitions. The localization exponent v is extracted with an approach based on the variable range hopping theory. We find the quantity v ≈ 2.3 at the second Landau level, which is proven to be accurately universal.

Ab initio Study of Electronic Structure and Magnetic Properties of Two Novel Neptunium （V） Sulfates： iaK3（ipO2）4（SO4）4（H2O）2 and iaipO2SO4H2O

Ab initio within the full potential linearized augmented plane wave （FP-LAPW） method with the GGA＋U approach is applied to study the electronic structures of two compounds NaK3（NpO2）4（SO4）4（H2O）2 and NaNpO2SO4H2O. The present calculations show that the major part of the spin magnetic moment in these two compounds is from Np（V） ions, and the origin of the cation-cation interactions between Np comes from the spin polarization effect within Np-ONv-Np bonds.

Delocalizedπ_(3)^(6) Bond in OX_(2) (X=Halogen) Molecules

OX_(2)(X=halogen)molecules was studied theoretically.Calculation results show that delocalizedπ_(3)^(6) bonds exist in their electronic structures and O atoms adopt the sp^(2) type of hybridization,which violates the prediction of the valence shell electron pair repulsion theory of sp^(3) type.Delocalization stabilization energy is proposed to measure the contribution of delocalizedπ_(3)^(6) bond to energy decrease and proves to bring extra-stability to the molecule.These phenomena can be summarized as a kind of coordinating effect.