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Density-functional approach to the three-body dispersion interaction based on the exchange dipole moment
We implement and compute the density functional nonadditive three-body dispersion interaction using a combination of Tang-Karplus formalism and the exchange-dipole moment model of Becke and Johnson. The computation of the C{sub 9} dispersion coefficients is done in a non-empirical fashion. The obtained C{sub 9} values of a series of noble atom triplets agree well with highly accurate values in the literature. We also calculate the C{sub 9} values for a series of benzene trimers and find a good agreement with high-level ab initio values reported recently in the literature. For the question of damping of the three-body dispersion at short distances, we propose two damping schemes and optimize them based on the benzene trimers data, and the fitted analytic potentials of He{sub 3} and Ar{sub 3} trimers fitted to the results of high-level wavefunction theories available from the literature. Both damping schemes respond well to the optimization of two parameters.
Light-induced ultrafast spin transport in multilayer metallic films originates from sp-d spin exchange coupling
Ultrafast interaction between the femtosecond laser pulse and the magnetic metal provides an efficient way to manipulate the magnetic states of matter. Numerous experimental advancements have been made on multilayer metallic films in the last two decades. However, the underlying physics remains unclear. Here, relying on an efficient ab initio spin dynamics simulation algorithm, we revealed the physics that can unify the progress in different experiments. We found that light-induced ultrafast spin transport in multilayer metallic films originates from the sp - d spin-exchange interaction, which can induce an ultrafast, large, and pure spin current from ferromagnetic metal to nonmagnetic metal without charge carrier transport. The resulting trends of spin demagnetization and spin flow are consistent with most experiments. It can explain a variety of ultrafast light-spin manipulation experiments with different systems and different pump-probe technologies, covering a wide range of work in this field.
Study of Self-Interaction Errors in Density Functional Calculations of Magnetic Exchange Coupling Constants Using Three Self-Interaction Correction Methods
We examine the role of self-interaction errors (SIE) removal on the evaluation of magnetic exchange coupling constants. In particular we analyze the effect of scaling down the self-interaction-correction (SIC) for three non-empirical density functional approximations (DFAs) namely, the local spin density approximation, the Perdew-Burke-Ernzerhof generalized gradient approximation, and recent SCAN family of meta-GGA functionals. To this end, we employ three one-electron SIC methods: Perdew-Zunger [Perdew, J. P.; Zunger, A. Phys. Rev. B, 1981, 23, 5048] SIC, the orbitalwise scaled SIC method [Vydrov, O. A. et al., J. Chem. Phys. 2006, 124, 094108], and the recent local scaling method [Zope, R. R. et al., J. Chem. Phys. 2019, 151, 214108]. We compute the magnetic exchange coupling constants using the spin projection and non projection approaches for sets of molecules composed of dinuclear and polynuclear H-He models, organic radical molecules, and chlorocuprate, and compare these results against accurate theories and experiment. Our results show that for the systems that mainly consist of single electron regions, PZSIC performs well but for more complex organic systems and the chlorcuprates, an overcorrecting tendency of PZSIC combined with the DFAs utilized in this work is more pronounced, and in such cases LSIC with kinetic energy density ratio performs better than PZSIC. Furthermore, analysis of the results in terms of SIC corrections to the density and to the total energy shows that both density and energy correction are required to obtain an improved prediction of magnetic exchange couplings.
Magnetism in curved geometries
Extending planar two-dimensional structures into the three-dimensional space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring the geometry of an object, e.g. its local curvature. In a generic electronic system, curvature results in the appearance of scalar and vector geometric potentials inducing anisotropic and chiral effects. In the specific case of magnetism, even in the simplest case of a curved anisotropic Heisenberg magnet, the curvilinear geometry manifests two exchange-driven interactions, namely effective anisotropy and antisymmetric exchange, i.e. Dzyaloshinskii–Moriya-like interaction. As a consequence, a family of novel curvature-driven effects emerges, which includes magnetochiral effects and topologically induced magnetization patterning, resulting in theoretically predicted unlimited domain wall velocities, chirality symmetry breaking and Cherenkov-like effects for magnons. The broad range of altered physical properties makes these curved architectures appealing in view of fundamental research on e.g. skyrmionic systems, magnonic crystals or exotic spin configurations. In addition to these rich physics, the application potential of three-dimensionally shaped objects is currently being explored as magnetic field sensorics for magnetofluidic applications, spin-wave filters, advanced magneto-encephalography devices for diagnosis of epilepsy or for energy-efficient racetrack memory devices. Finally, these recent developments ranging from theoretical predictions over fabrication of three-dimensionally curved magnetic thin films, hollow cylinders or wires, to their characterization using integral means as well as the development of advanced tomography approaches are in the focus of this review.
Highly efficient removal of both cationic and anionic dyes from wastewater with a water-stable and eco-friendly Fe-MOF via host-guest encapsulation
Here, a water-stable cationic Fe based metal organic framework, CPM-97-Fe, was successfully synthesized in a large scale by a modified method (CPM: Crystalline Porous Materials). The adsorption behaviors, including removal efficiency, adsorption kinetics and isotherms of nine hazardous dyes in wastewater were investigated with different pH and organic solvents. The pseudo-second-order adsorption rate constant follows the order of Reactive Brilliant Red X-3B (X-3B, 0.0205 g mg -1 min -1 ) > Acid orange 7 (AO7, 0.0112 g mg -1 min -1 ) > Congo Red (CR, 0.0080 g mg -1 min -1 ) > Methylene Blue (MB, 0.0061 g mg -1 min -1 ) > Rhodamine B (RhB, 0.0049 g mg -1 min -1 ) > Croscein Scarlet 3B (CS3B, 0.0041 g mg -1 min -1 ) > Methyl Blue (MB, 0.0017 g mg -1 min -1 ) = New Coccine (NC, 0.0017 g mg -1 min -1 ) > Acid Black 1 (AB1, 0.0014 g mg -1 min -1 ). It is found that the adsorption quasi-equilibrium can reach quickly within 30 min, but the dyes with proper structure (i.e. proper distance between two sulfonic groups, less azo benzene hindrance effect, more reactive Cl groups, and more benzene rings), smaller molecular size, more negative charges, lower molecular mass favor the faster adsorption. The adsorption capacity obeys another sequence of CR (831 mg g -1 ) > X-3B (648 mg g -1 ) > AO7 (502 mg g -1 ) > MLB (380 mg g -1 ) > CS3B (356 mg g -1 ) > AB1 (325 mg g -1 ) > RhB (306 mg g -1 ) > MB (304 mg g -1 ) > NC (157 mg g -1 ). It is disclosed that CPM-97-Fe can adsorb more dyes with larger molecular mass, less negative charges, and a proper structure. Especially for Congo red, the adsorption capacity on CPM-97-Fe is 831 mgg -1 , 8.1 times that on activated carbon (103 mgg -1 ). Even the adsorption capacities of very bulky Rhodamine B and Methyl Blue reach as high as 306 and 304 mgg -1 , respectively, ranking the highest level among MOF materials. Moreover, the special structure of CPM-97-Fe with big open windows and high specific surface area of 1397.0 m 2 g -1 contributes to the fast adsorption and high capacity towards all investigated dyes via the host-guest encapsulation mechanism including electrostatic interaction, ion exchange, π-π stacking interaction, as well as pore filling.
Electron-Ion Collider - science and concept
Quantum Chromodynamics (QCD) is the fundamental quantum theory of quarks and gluons that make up almost all the visible matter in the universe. Quarks interact by exchanging gluons, but gluons also interact with gluons, a unique feature of QCD. Despite being so central to QCD, the properties and dynamics of gluons remain largely unexplored. The inspiration to solve the profound mysteries surrounding this ‘glue’ drives the development of a next-generation facility, the Electron-Ion Collider (EIC).
Regularization of the Coulomb singularity in exact exchange by Wigner-Seitz truncated interactions: Towards chemical accuracy in nontrivial systems
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Strong Kitaev Interaction in BaCo 2 (AsO 4 ) 2
The inelastic neutron scattering results and their analysis unequivocally point to a dominant Kitaev interaction in the honeycomb-lattice cobaltate BaCo 2 (AsO 4 ) 2 . Our anisotropic-exchange model closely describes all available neutron scattering data in the material’s field-polarized phase. Furthermore, the density-matrix renormalization group results for our model are in close accord with the unusual double-zigzag magnetic order and the low in-plane saturation field of BaCo 2 (AsO 4 ) 2 .
Crystalline solutions of the Kohn-Sham equations in the fractional quantum Hall regime
A Kohn-Sham density functional approach has recently been developed for the fractional quantum Hall effect, which maps the strongly interacting electrons into a system of weakly interacting composite fermions subject to an exchange correlation potential as well as a density dependent gauge field that mimics the "flux quanta" bound to composite fermions. To get a feel for the role of various terms, we study the behavior of the self-consistent solution as a function of the strength of the exchange correlation potential, which is varied through an ad hoc multiplicative factor. Here, we find that a crystal phase is stabilized when the exchange correlation interaction is sufficiently strong relative to the composite-fermion cyclotron energy. Various properties of this crystal are examined.
Controlling the Topological Sector of Magnetic Solitons in Exfoliated Cr 1 / 3 NbS 2 Crystals
Here, we investigate manifestations of topological order in monoaxial helimagnet Cr 1/3 NbS 2 by performing transport measurements on ultrathin crystals. Upon sweeping the magnetic field perpendicularly to the helical axis, crystals thicker than one helix pitch (48 nm) but much thinner than the magnetic domain size (similar to 1 mu m) are found to exhibit sharp and hysteretic resistance jumps. We also show that these phenomena originate from transitions between topological sectors with a different number of magnetic solitons. This is confirmed by measurements on crystals thinner than 48 nm-in which the topological sector cannot change-that do not exhibit any jump or hysteresis. These results show the ability to deterministically control the topological sector of finite-size Cr 1/3 NbS 2 and to detect intersector transitions by transport measurements.
Spin waves in ultracold gases with exchange and spin-orbit interactions
The dynamics of spin waves in ultracold gases is investigated with allowance for exchange and spin-orbit interaction. The exact basis of atomic states is used taking into account all rotational quantum numbers of the atom. The dispersion relation for spin waves is obtained for fermions and bosons in the hydro-dynamic approximation.
Search for exotic spin-dependent interactions with a spin-exchange relaxation-free magnetometer
We propose a novel experimental approach to explore exotic spin-dependent interactions using a spin-exchange relaxation-free (SERF) magnetometer, the most sensitive noncryogenic magnetic-field sensor. This approach studies the interactions between optically polarized electron spins located inside a vapor cell of the SERF magnetometer and unpolarized or polarized particles of external solid-state objects. The coupling of spin-dependent interactions to the polarized electron spins of the magnetometer induces the tilt of the electron spins, which can be detected with high sensitivity by a probe laser beam similarly as an external magnetic field. Lastly, we estimate that by moving unpolarized or polarized objects next to the SERF Rb vapor cell, the experimental limit to the spin-dependent interactions can be significantly improved over existing experiments, and new limits on the coupling strengths can be set in the interaction range below 10 –2 m.
Phase Transitions in the Antiferromagnetic Heisenberg Model on a Body-Centered Cubic Lattice with Allowance for the Next-Nearest-Neighbor Interactions
Based on the replica exchange Monte Carlo algorithm and histogram analysis of data, the phase transitions in the three-dimensional antiferromagnetic Heisenberg model on a body-centered cubic lattice with allowance for the next-nearest-neighbor interaction are studied. The study is performed for the nextnearest- neighbor exchange interaction ratio of r = 1. It is established that, for this model, the transition from the antiferromagnetic to paramagnetic phase is a first-order phase transition.
Mutual interactions of redox couples via electron exchange in silicate melts - Models for geochemical melt systems
The mutual interactions via electron exchange of redox couples in glass-forming melts were investigated both theoretically and experimentally. A thermodynamic approach for considering the mutual interactions leads to conclusion that the degree of mutual interaction in the melt should be proportional in part to the difference in relative reduction potentials of the interacting redox couples. Experimental studies verify this conclusion for numerous redox couples in several composition/temperature/oxygen fugacity regimes. Geochemical systems simultaneously possess many potentially multivalent elements; the stabilized redox states in the resulting magmas can be explained in part by mutual interactions and by redox buffering through the central Fe(III)- Fe(II) couples in the melts. The significance of these results for basaltic magmas of the earth, moon, and meteorites is addressed.
Silicon Qubits
There are two good reasons to attempt to build quantum bits (qubits) out of silicon. The first is the obvious foundation of classical microelectronics. Although silicon quantum computers would operate in a fundamentally different way from classical computers$-$for example, at cryogenic temperatures$-$still the level of development in material quality, crystal growth, and fabrication methodologies for silicon is unrivaled by any other material in the world. Leveraging even a small fraction of the worldwide investment in silicon for qubit development could potentially put silicon-based qubits far ahead of other solid-state alternatives. The second, less obvious reason for choosing silicon is the remarkably clean magnetic environment witnessed by spins in highly purified and isotopically enriched silicon material. Fortuitously, 95.3% of the naturally occurring isotopes of Si nuclei ( 28 Si and 30 Si) are spin-0. These nuclei therefore have a “closed shell” of nuclear moments, providing no external magnetic field whatsoever. Add to this the possibility of intrinsic silicon with part-per-billion chemical quality and the system is remarkably close to “vacuum” with respect to magnetic noise properties.
Structural, electronic, magnetic, and magnetocaloric properties in metallic antiperovskite compound Mn3GaC
Highlights: • We have studied the magnetocaloric effect of the metallic antiperovskite compound Mn{sub 3}GaC. • We used the ab-initio calculations, the Monte Carlo simulations and mean field theory. • A second-order ferromagnetic-paramagnetic phase transition about T{sub C} ∼ 249 K. • The magnetic moment and the exchange coupling interactions are calculated. - Abstract: The structural, electronic, magnetic, and magnetocaloric properties of the metallic antiperovskite compound Mn{sub 3}GaC were investigated using several theoretical methods such as: First principle calculations, Monte Carlo simulations and mean field theory. The metallic antiperovskite compound Mn{sub 3}GaC exhibits a second-order ferromagnetic-paramagnetic phase transition around T{sub C} = 249 K. Using the first principle calculations, the magnetic moment and the exchange coupling interactions values are 1.37 μ{sub B} and J{sub 1} = 35.78meV, J{sub 2} = 40.16meV, respectively. The total magnetization, the susceptibility and the specific heat of this compound are calculated. The critical temperature obtained is in good agreement with the experimental results. Obviously, the large MCE with no hysteresis loss is obtained around T{sub C}. The maximum values of the magnetic entropy change (ΔS{sub mag}), adiabatic temperature change (ΔT{sub ad}) and the relative cooling power (RCP) are 13.41 J/kg.K, 15.96 K, 748 J/kg respectively, under applied an external magnetic field of h = 5.0 T.
Probing the Deuteron at Very Large Internal Momenta
We measure H-2(e, e' p)n cross sections at 4-momentum transfers of Q(2) = 4.5 +/- 0.5 (GeV/c)(2) over a range of neutron recoil momenta p(r), reaching up to similar to 1.0 GeV/c. We obtain data at fixed neutron recoil angles theta(nq) = 35 degrees, 45 degrees, and 75 degrees with respect to the 3-momentum transfer (q)over-right-arrow. The new data agree well with previous data, which reached p(r) similar to 500 MeV/c. At theta(nq) = 35 degrees and 45 degrees, final state interactions, meson exchange currents, and isobar currents are suppressed and the plane wave impulse approximation provides the dominant cross section contribution. We compare the new data to recent theoretical calculations, where we observe a significant discrepancy for recoil momenta P-r > 700 MeV/c.