Strong Local Interactions Research Articles

Construction of Monoatomic-Modified Defective Ti4+αTi3+1-αO2-δ Nanofibers for Photocatalytic Oxidation of HMF to Valuable Chemicals.

Efficiently upgrading 5-hydroxymethylfurfural (HMF) into high-value-added products, such as 2,5-diformylfuran (DFF) and 2,5-furan dicarboxylic acid (FDCA), through a photocatalytic process by using solar energy has been incessantly pursued worldwide. Herein, a series of transition-metal (TM = Ni, Fe, Co, Cu) single atoms were supported on Ti4+αTi3+1-αO2-δ nanofibers (NFs) with certain defects (Ov), denoted as TM SAC-Ti4+αTi3+1-αO2-δ NFs (TM = Ni, Fe, Co, Cu), aiming to enhance the photocatalytic conversion of HMF. A super HMF conversion rate of 57% and a total yield of 1718.66 μmol g-1 h-1 (DFF and FDCA) surpassing that of the Ti4+αTi3+1-αO2-δ NFs by 1.6 and 2.1 times, respectively, are realized when TM is Co (Co SAC-Ti4+αTi3+1-αO2-δ NFs). Experiments combined with density functional theory calculation (DFT) demonstrate that the TM single atoms occupy the Ti site of Ti4+αTi3+1-αO2-δ NFs, which plays a dominant role in the photo-oxidation of HMF. Raman, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) characterizations confirm the strong electron local exchange interaction in TM SAC-Ti4+αTi3+1-αO2-δ NFs and demonstrate the substitution of Ti by the TM SACs. The projected density of states and charge density difference reveal that the strong interaction between metal-3d and O-2p orbitals forms Ti-O-TM bonds. The bonds are identified as the adsorption site, where TM single atoms on the surface of Ti4+αTi3+1-αO2-δ NFs reduce HMF molecule adsorption energy (Eads). Furthermore, the TM single atom modulates the electronic structure of TM SAC-Ti4+αTi3+1-αO2-δ NFs through electron transfer, leading to narrow band gaps of the photocatalysts and enhancing their photocatalytic performance. This study has uncovered a newer strategy for enhancing the photocatalytic attributes of semiconducting materials.

The carbonyl-lock mechanism underlying non-aromatic fluorescence in biological matter

Challenging the basis of our chemical intuition, recent experimental evidence reveals the presence of a new type of intrinsic fluorescence in biomolecules that exists even in the absence of aromatic or electronically conjugated chemical compounds. The origin of this phenomenon has remained elusive so far. In the present study, we identify a mechanism underlying this new type of fluorescence in different biological aggregates. By employing non-adiabatic ab initio molecular dynamics simulations combined with a data-driven approach, we characterize the typical ultrafast non-radiative relaxation pathways active in non-fluorescent peptides. We show that the key vibrational mode for the non-radiative decay towards the ground state is the carbonyl elongation. Non-aromatic fluorescence appears to emerge from blocking this mode with strong local interactions such as hydrogen bonds. While we cannot rule out the existence of alternative non-aromatic fluorescence mechanisms in other systems, we demonstrate that this carbonyl-lock mechanism for trapping the excited state leads to the fluorescence yield increase observed experimentally, and set the stage for design principles to realize novel non-invasive biocompatible probes with applications in bioimaging, sensing, and biophotonics.

Kelvin–Helmholtz Instability “Tube” and “Knot” Dynamics. Part I: Expanding Observational Evidence of Occurrence and Environmental Influences

Abstract Multiple recent observations in the mesosphere have revealed large-scale Kelvin–Helmholtz instabilities (KHI) exhibiting diverse spatial features and temporal evolutions. The first event reported by Hecht et al. exhibited multiple features resembling those seen to arise in early laboratory shear-flow studies described as “tube” and “knot” (T&K) dynamics by Thorpe. The potential importance of T&K dynamics in the atmosphere, and in the oceans and other stratified and sheared fluids, is due to their accelerated turbulence transitions and elevated energy dissipation rates relative to KHI turbulence transitions occurring in their absence. Motivated by these studies, we survey recent observational evidence of multiscale Kelvin–Helmholtz instabilities throughout the atmosphere, many features of which closely resemble T&K dynamics observed in the laboratory and idealized initial modeling. These efforts will guide further modeling assessing the potential importance of these T&K dynamics in turbulence generation, energy dissipation, and mixing throughout the atmosphere and other fluids. We expect these dynamics to have implications for parameterizing mixing and transport in stratified shear flows in the atmosphere and oceans that have not been considered to date. Companion papers describe results of a multiscale gravity wave direct numerical simulation (DNS) that serendipitously exhibits a number of KHI T&K events and an idealized multiscale DNS of KHI T&K dynamics without gravity wave influences. Significance Statement Kelvin–Helmholtz instabilities (KHI) occur throughout the atmosphere and induce turbulence and mixing that need to be represented in weather prediction and other models of the atmosphere and oceans. This paper documents recent atmospheric evidence for widespread, more intense, features of KHI dynamics that arise where KH billows are initially discontinuous, misaligned, or varying along their axes. These features initiate strong local vortex interactions described as “tubes” and “knots” in early laboratory experiments, suggested by, but not recognized in, earlier atmospheric and oceanic profiling, and only recently confirmed in newer, high-resolution atmospheric imaging and idealized modeling to date.

Suppression of local electron-phonon interaction in pi-conjugated oligomers and its monitoring using Raman scattering

For efficient operation of many organic electronic devices, organic semiconductors with high charge carrier mobility are required. However, in most of the known organic semiconductors, the charge mobility is low, since it is limited by the strong local electron-phonon interaction. In the present work, using the example of thiophene-phenylene co-oligomers, a class of organic semiconductors that combine a sufficiently high charge mobility with light emission and therefore promising for light-emitting transistors and electrically pumped lasers, the mechanism of suppression of the electron-phonon interaction by introducing electronegative atoms or an additional thiophene ring is studied. It was found that such structural changes alter the contribution of various vibrational modes to the local electron-phonon interaction, in particular, to the suppression of the contribution of the low-frequency torsion mode. In addition, it is shown that for the two modes that make the largest contribution to the local electron-phonon interaction in an unsubstituted oligomer, this change correlates with their intensity of Raman scattering, and this confirms the promise of studying the electron-phonon interaction using Raman spectroscopy. The results obtained improve the understanding of the relationship between the local electron-phonon interaction and the molecular structure of organic semiconductors, which is extremely important for the directed design of such materials with high charge mobility.

Multicellular aligned bands disrupt global collective cell behavior.

Mechanical stress patterns emerging from collective cell behavior have been shown to play critical roles in morphogenesis, tissue repair, and cancer metastasis. In our previous work, we constrained valvular interstitial cell (VIC) monolayers on circular protein islands to study emergent behavior in a controlled manner and demonstrated that the general patterns of cell alignment, size, and apoptosis correlate with predicted mechanical stress fields if radially increasing stiffness or contractility are used in the computational models. However, these radially symmetric models did not predict the existence of local regions of dense aligned cells observed in seemingly random locations of individual aggregates. The goal of this study is to determine how the heterogeneities in cell behavior emerge over time and diverge from the predicted collective cell behavior. Cell-cell interactions in circular multicellular aggregates of VICs were studied with time-lapse imaging ranging from hours to days, and migration, proliferation, and traction stresses were measured. Our results indicate that elongated cells create strong local alignment within preconfluent cell populations on the microcontact printed protein islands. These cells influence the alignment of additional cells to create dense, locally aligned bands of cells which disrupt the predicted global behavior. Cells are highly elongated at the endpoints of the bands yet have decreased spread area in the middle and reduced mobility. Although traction stresses at the endpoints of bands are enhanced, even to the point of detaching aggregates from the culture surface, the cells in dense bands exhibit reduced proliferation, less nuclear YAP, and increased apoptotic rates indicating a low stress environment. These findings suggest that strong local cell-cell interactions between primary fibroblastic cells can disrupt the global collective cellular behavior leading to substantial heterogeneity of cell behaviors in constrained monolayers. This local emergent behavior within aggregated fibroblasts may play an important role in development and disease of connective tissues. STATEMENT OF SIGNIFICANCE: Mechanical stress patterns emerging from collective cell behavior play critical roles in morphogenesis, tissue repair, and cancer metastasis. Much has been learned of these collective behaviors by utilizing microcontact printing to constrain cell monolayers (aggregates) into specific shapes. Here we utilize these tools along with long-term video microscopy tracking of individual aggregates to determine how heterogeneous collective behaviors unique to primary fibroblastic cells emerge over time and diverge from computed stress fields. We find that dense multicellular bands form from local collective behavior and disrupt the global collective behavior resulting in heterogeneous patterns of migration, traction stresses, proliferation, and apoptosis. This local emergent behavior within aggregated fibroblasts may play an important role in development and disease of connective tissues.

Heterogeneous Interface Catalysts with Electron Local Exchange toward Highly Selective Oxidation of Biomass Platform Compounds

Catalytic oxidation conversion of biomass-derived compounds to high value-added products has aroused intensive research interest. Herein, we report a Co3O4/Co2MnO4 metal oxide composites catalyst prepared from layered double hydroxides precursors, which is featured with a uniformly interdispersed two-phase heterogeneous interface. This sample exhibits an enhanced catalytic performance for the selective oxidation reaction of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid with a yield of 98%. A combination study including high-resolution transmission electron microscopy (HR-TEM), X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS), and Raman confirms that a strong electron local exchange interaction occurs at the Co3O4/Co2MnO4 heterogeneous interface with electron transfer from Mn in the spinel to Co in the oxide. Both experimental investigations (quasi-in situ XPS, in situ Fourier transform infrared spectroscopy (FTIR), and in situ Raman) and theoretical calculations substantiate that the interfacial metal–oxygen bridge (Co2+–O–Mn4+) serves as an intrinsic active site in determining the reaction pathway: the C═O group in the reactant undergoes activated adsorption at Mn4+, followed by the escape of interfacial lattice oxygen and the oxidation of the aldehyde group to carboxylic acid; subsequently, the O2 molecule undergoes dissociation at the in situ generated oxygen vacancy. This electron local exchange interaction facilitates the mobility of interfacial lattice oxygen, whose universality is demonstrated in catalytic oxidation of other 11 biomass-derived furanoids to the corresponding carboxylic acids.

Concentration Phenomena in Fitzhugh–Nagumo Equations: A Mesoscopic Approach

We consider a spatially extended mesoscopic FitzHugh–Nagumo model with strong local interactions and prove that its asymptotic limit converges towards the classical nonlocal reaction-diffusion FitzHugh–Nagumo system. As the local interactions strongly dominate, the weak solution to the mesoscopic equation under consideration converges to the local equilibrium, which has the form of a Dirac distribution concentrated to an averaged membrane potential.

The Role of Electrostatic Interactions in IFIT5-RNA Complexes Predicted by the UBDB+EPMM Method.

Electrostatic energy has a significant contribution to intermolecular interaction energy, especially in biological systems. Unfortunately, precise quantum mechanics calculations are not feasible for large biological systems; hence, simpler calculation methods are required. We propose a method called UBDB+EPMM (University at Buffalo Pseudoatom DataBank + Exact Potential Multipole Moments), which shortens computational time without losing accuracy. Here, we characterize electrostatic interactions in selected complexes of IFIT proteins with RNA. IFIT proteins are effectors of the innate immune system, and by binding foreign RNA, they prevent the synthesis of viral proteins in human host cells; hence, they block the propagation of viruses. We show that by using the UBDB+EPMM method it is possible to describe protein-RNA interactions not only qualitatively but also quantitatively. Looking at the charge penetration contribution to electrostatic interactions, we find all amino acid residues with strong local interactions. Moreover, we confirm that electrostatic interaction of IFIT5 with pppRNA does not depend on the sequence of the RNA.

Dynamical correlations in single-layer CrI3

Chromium triiodide is an intrinsically magnetic van der Waals material down to the single-layer limit. Here, we provide a first-principles description of finite-temperature magnetic and spectral properties of monolayer (ML) ${\mathrm{CrI}}_{3}$ based on fully charge self-consistent density functional theory (DFT) combined with dynamical mean-field theory, revealing a formation of local moments on Cr from strong local Coulomb interactions. We show that the presence of local dynamical correlations leads to a modification of the electronic structure of ferromagnetically ordered ${\mathrm{CrI}}_{3}$. In contrast to conventional $\mathrm{DFT}+U$ calculations, we find that the top of the valence band in ML ${\mathrm{CrI}}_{3}$ demonstrates essentially different orbital character for minority and majority spin states, which is closer to the standard DFT results. This leads to a strong spin polarization of the optical conductivity upon hole doping, which could be verified experimentally.

Soft‐wall ion transfer channel accurately predicts sterically hindered ion channel permeability

AbstractWe provide a simple and systematic computational model to study ion channel permeability using density functional theory. While existing permeability models with a hard‐wall steric hindrance factor work reasonably well for large ions, they severely inhibit the permeation of small ions through channel pores. Here, by introducing a steric hindrance factor that allows pore expansion due to intrinsically soft ion transfer channel walls, the new permeability model accurately describes the effect of steric hindrance stemming from the soft and flexible ion channel wall. Most importantly, the soft‐wall ion transfer channel model works for a wide range of ionic radii from fluoride to gluconate. In addition, we show that strong local electrostatic interaction between densely charged ions such as fluoride and bicarbonate and ion channels with ion binding sites significantly promotes the permeation processes.

Material Science for catalysis: Quo vadis?

Material Science for catalysis: Quo vadis?

Study on mass erosion model of projectile penetrating concrete at high speed considering variation of friction coefficient

When the projectile penetrates into the concrete medium at high speed, the mass loss and nose blunting occur due to the strong local interaction between the projectile and the target. In order to further explore the mass erosion effect of high-speed projectile penetrating concrete target and its influencing factors, based on the thermal melting mechanism and variable friction coefficient model, the mass erosion model of high-speed projectile penetrating concrete target was modified considering the change of projectile nose shape during penetration. In order to verify the reliability of the model, based on the 30 mm ballistic gun platform, the oval projectile penetrating typical concrete targets at high velocities ranging from 700 to 1000 m/s was carried out, and the mass erosion results of high-speed penetration were obtained. Combined with the theoretical model, the reliability of the modified model is verified by analyzing the test data in this paper and the literature. The results show that the sliding friction term accounts for 10%−40% of the total friction in the process of projectile penetration, and its influence on the penetration process can’t be ignored. The prediction results of mass erosion model considering the variation of friction coefficient are in good agreement with the existing test data, and the maximum error with the test data in this paper is less than 7%, which can accurately predict the mass loss of projectile under different working conditions.

Small to large Fermi surface transition in a single-band model using randomly coupled ancillas

We describe a solvable model of a quantum transition in a single band model involving a change in the size of the electron Fermi surface without any symmetry breaking. In a model with electron density $1-p$, we find a 'large' Fermi surface state with the conventional Luttinger volume $1-p$ of electrons for $p>p_c$, and a first order transition to a 'small' Fermi surface state with a non-Luttinger volume $p$ of holes for $p<p_c$. As required by extended Luttinger theorems, the small Fermi surface state also has fractionalized spinon excitations. The model has electrons with strong local interactions in a single band; after a canonical transformation, the interactions are transferred to a coupling to two layers of ancilla qubits, as proposed by Zhang and Sachdev (Phys. Rev. Research ${\bf 2}$, 023172 (2020)). Solvability is achieved by employing random exchange interactions within the ancilla layers, and taking the large $M$ limit with SU($M$) spin symmetry, as in the Sachdev-Ye-Kitaev models. The local electron spectral function of the small Fermi surface phase displays a particle-hole asymmetric pseudogap, and maps onto the spectral function of a lightly doped Kondo insulator of a Kondo-Heisenberg lattice model. We discuss connections to the physics of the hole-doped cuprates: the asymmetric pseudogap observed in STM, and the sudden change from incoherent to coherent anti-nodal spectra observed recently in photoemission. A holographic analogy to wormhole transitions between multiple black holes is briefly noted.

Lattice symmetry and emergence of antiferromagnetic quantum Hall states

Strong local interaction in systems with non-trivial topological bands can stabilize quantum states such as magnetic topological insulators. We investigate the influence of the lattice symmetry on the possible emergence of antiferromagnetic quantum Hall states. We consider the spinful Harper-Hofstadter model extended by a next-nearest-neighbor (NNN) hopping which opens a gap at half-filling and allows for the realization of a quantum Hall insulator. The quantum Hall insulator has the Chern number $\mathcal{C}=2$ as both spin components are in the same quantum Hall state. We add to the system a staggered potential $\Delta$ along the $\hat{x}$-direction favoring a normal insulator and the Hubbard interaction $U$ favoring a Mott insulator. The Mott insulator is a N\'eel antiferromagnet for small and a stripe antiferromagnet for large NNN hopping. We investigate the $U$-$\Delta$ phase diagram of the model for both small and large NNN hoppings. We show that while for large NNN hopping there exists a $\mathcal{C}=1$ stripe antiferromagnetic quantum Hall insulator in the phase diagram, there is no equivalent $\mathcal{C}=1$ N\'eel antiferromagnetic quantum Hall insulator at the small NNN hopping. We discuss that a $\mathcal{C}=1$ antiferromagnetic quantum Hall insulator can emerge only if the effect of the spin-flip transformation cannot be compensated by a space group operation. Our findings can be used as a guideline in future investigations searching for antiferromagnetic quantum Hall states.

Asymptotic preserving schemes for the FitzHugh–Nagumo transport equation with strong local interactions

This paper is devoted to the numerical approximation of the spatially extended FitzHugh–Nagumo transport equation with strong local interactions based on a particle method. In this regime, the time step can be subject to stability constraints related to the interaction kernel. To avoid this limitation, our approach is based on higher-order implicit-explicit numerical schemes. Thus, when the magnitude of the interactions becomes large, this method provides a consistent discretization of the macroscopic reaction-diffusion FitzHugh–Nagumo system. We carry out some theoretical proofs and perform several numerical experiments that establish a solid validation of the method and its underlying concepts.

Emergent chiral symmetry in a three-dimensional interacting Dirac liquid

We compute the effects of strong Hubbardlike local electronic interactions on three-dimensional four-component massless Dirac fermions, which in a noninteracting system possess a microscopic global U(1) ⊗ SU(2) chiral symmetry. A concrete lattice realization of such chiral Dirac excitations is presented, and the role of electron-electron interactions is studied by performing a field theoretic renormalization group (RG) analysis, controlled by a small parameter ϵ with ϵ = d−1, about the lower-critical one spatial dimension. Besides the noninteracting Gaussian fixed point, the system supports four quantum critical and four bicritical points at nonvanishing interaction couplings ∼ ϵ. Even though the chiral symmetry is absent in the interacting model, it gets restored (either partially or fully) at various RG fixed points as emergent phenomena. A representative cut of the global phase diagram displays a confluence of scalar and pseudoscalar excitonic and superconducting (such as the s-wave and p-wave) mass ordered phases, manifesting restoration of (a) chiral U(1) symmetry between two excitonic masses for repulsive interactions and (b) pseudospin SU(2) symmetry between scalar or pseudoscalar excitonic and superconducting masses for attractive interactions. Finally, we perturbatively study the effects of weak rotational symmetry breaking on the stability of various RG fixed points.

Magnetocaloric Ln(HCO2)(C2O4) frameworks: synthesis, structure and magnetic properties

Gd(HCO2)(C2O4) is an excellent magnetocaloric with Ising analogues lacking the strong local interactions needed to outperform it at higher temperatures.

Effect of carbon vacancies and oxygen impurities on the dynamical and thermal properties of uranium monocarbide

An influence of carbon vacancies and substitutional oxygen impurities on the phonon dynamics and thermal properties of uranium monocarbide is investigated within the density functional theory incorporating strong local Coulomb and spin-orbit interactions. Anharmonicity of lattice vibrations is taken into account via the quasi-harmonic theory. Results obtained for the modeled UC1−x and UC1−xOx compositions with x=3% show that the changes in atomic displacements and force constants induced by mono-vacancies and substitutional oxygen impurities in the carbon sublattice of UC remain restricted to the immediate neighborhood of the incorporated defects. The most sensitive to point defects in the carbon sublattice of UC are the optical phonon branches, while the phonon densities of states and the phonon-dependent thermodynamical properties remain affected to a lesser extent. The X-ray powder diffraction experiments have been performed to examine the temperature evolution of the lattice parameter of highly stoichiometric UC between 20 and 310 K. The present experimental studies supplement existing literature data by extending description of the uranium monocarbide structure below room temperature. They also support and validate our theoretical predictions about behavior of the investigated system at low temperatures.

Parameter-free hybridlike functional based on an extended Hubbard model: DFT+U+V

In this article, we propose an energy functional at the level of DFT+U+V that allows us to compute self-consistently the values of the on-site interaction, Hubbard U and Hund J, as well as the intersite interaction V. This functional extends the previously proposed ACBN0 functional [Phys. Rev. X 5, 011006 (2015)] including both on-site and intersite interactions. We show that this ab initio self-consistent functional yields improved electronic properties for a wide range of materials, ranging from $sp$ materials to strongly-correlated materials. This functional can also be seen as an alternative general and systematic way to construct parameter-free hybrid functionals, based on the extended Hubbard model and a selected set of Coulomb integrals, and might be used to develop novel approximations. By extending the DFT+U method to materials where strong local and nonlocal interactions are relevant, this work opens the door to the ab initio study the electronic, ionic, and optical properties of a larger class of strongly correlated materials in and out of equilibrium.

CFD-DEM study of particle-fluid flow and retention performance of sand screen

Sand screens are widely used to control sand production in unconsolidated reservoirs. Because of the lack of insightful understanding of this process, to date, reliably optimizing screen size is still a challenge. This paper presents a numerical study of the sand retention and production behaviors for widely used wire-wrapped screens by means of the combined approach of computational fluid dynamic (CFD) and discrete element method (DEM). The validity of the model has been verified by comparing the predicted critical slot sizes and sand production with published experimental results. On this basis, the effects of slot width-particle size ratios and wetting fluids, including gas and crude oil, are studied. The numerical results show that the increase in size ratio increases sand production, and the presence of fluid flow enhances sand production and causes unstable sand retention, which is more significant for crude oil compared to gas. Also, three mechanisms that allow the sand retention over a screen are identified, including stable bridging, bridging with intermittent collapse, and bridging with continuous collapse. Wetting fluids play an essential role in the sand production and bridging when the particle-fluid forces exerted on the particles near the slot are significant. Such forces induce strong localized particle-particle interactions in the nearby region over the slot, which accounts for the unstable bridging behavior.