Self-consistent Study Research Articles

Self-consistent study of topological superconductivity in two-dimensional quasicrystals

Self-consistent study of topological superconductivity in two-dimensional quasicrystals

Nonlinear Treatment of a Black Hole Mimicker Ringdown.

We perform the first nonlinear and self-consistent study of the merger and ringdown of a black hole mimicking object with stable light rings. To that end, we numerically solve the full Einstein-Klein-Gordon equations governing the head-on collisions of a series of binary boson stars in the large-mass-ratio regime resulting in spinning horizonless remnants with stable light rings. We broadly confirm the appearance of features in the extracted gravitational waveforms expected based on perturbative methods: the signal from the prompt response of the remnants approaches that of a Kerr black hole in the large-compactness limit, and the subsequent emissions contain periodically appearing bursts akin to so-called gravitational wave echoes. However, these bursts occur at high frequencies and are sourced by perturbations of the remnant's internal degrees of freedom. Furthermore, the emitted waveforms also contain a large-amplitude and long-lived component comparable in frequency to black hole quasinormal modes. We further characterize the emissions, obtain basic scaling relations of relevant timescales, and compute the energy emitted in gravitational waves.

Zero-Field Splitting Tensor of the Triplet Excited States of Aromatic Molecules: A Valence Full-π Complete Active Space Self-Consistent Field Study.

A method to predict the D tensor in the molecular frame with multiconfigurational wave functions in large active space was proposed, and the spin properties of the lowest triplets of aromatic molecules were examined with full-π active space; such calculations were challenging because the size of active space grows exponentially with the number of π electrons. In this method, the exponential growth of complexity is resolved by the density matrix renormalization group (DMRG) algorithm. From the D tensor, we can directly determine the direction of the magnetic axes and the ZFS parameters, D- and E-values, of the phenomenological spin Hamiltonian with their signs, which are not usually obtained in ESR experiments. The method using the DMRG-CASSCF wave function can give correct results even when the sign of D- and E-values is sensitive to the accuracy of the prediction of the D tensor and existing methods fail to predict the correct magnetic axes.

Theoretical Study of Raman Intensities of p-Nitroaniline in Different Solvent Conditions by Using a Reference Interaction Site Model Self-Consistent Field Explicitly Including Constrained Spatial Electron Density Distribution.

Raman spectroscopy is one of the most powerful tools to understand and characterize the states and structures of systems in several environments. To obtain highly accurate changes in Raman intensities of systems in solution, theoretical treatment, which can deal with not only the states and structures of systems but also the environment around molecules, proves to be significant. Hence, in this study, we developed the calculation of changes in Raman intensities of systems in different solvent conditions by using the reference interaction site model self-consistent field study explicitly including constrained spatial electron density distribution; this model is designed based on elements from both quantum mechanics and statistical mechanics. We showed that our calculation method could reproduce the changes in Raman intensities of p-nitroaniline (pNA) under different solvent conditions, including supercritical water, which has been observed in previous experimental studies. Based on the analysis of the calculation results, we observed that the ratio of the Raman intensity change of pNA in different solvent conditions is strongly correlated with the charge-transfer character of pNA.

Self-consistent study of tearing mode with finite current gradient in the resistive-inertial and viscous-resistive regimes

Via the two-field reduced magneto-hydrodynamics model, a self-consistent theory of tearing mode evolution is developed to study the stability of tearing mode in the resistive-inertial and viscous-resistive regimes. Based on the series expansion method, we obtain a closed system for tearing mode evolution with the finite current gradient (FCG) effect. Solving the closed system with correlated approximations, the dispersion relation of tearing mode with FCG in the resistive-inertial and resistive-viscous regimes is derived and discussed. Self-consistent calculations adopted in this work show that assumptions used in previous studies are not always appropriate. Furthermore, deviation from those assumptions provides a non-negligible effect to the stability of tearing mode.

Self-Consistent Calculation of Nuclear Charge Radii in K Isotopes

Fully self-consistent study of the charge radii in Ca region is exemplified by the calculation in the long chains of K isotopes. The neutron-deficient and neutron-rich nuclei with pairing in both neutron and proton sectors, as well as the (semi-) magic nuclei around the closed neutron shells at N = 20, 28, 32 are treated within the Energy Density Functional (EDF) approach with the Fayans functional DF3-a. The performance of the DF3-a is analysed in describing the odd-even staggering effects found both in previous and in more recent CERN-ISOLDE experiments for 36–52K isotopes.

Self-Consistent Study of the Ground State and β-Decay Properties in C, N, O Region

Self-Consistent Study of the Ground State and β-Decay Properties in C, N, O Region

Microstructure characterization and elastic-plastic self-consistent simulation studies of anisotropic deformation of [formula omitted]-tin

Uniaxial compression tests of 99.9% pure polycrystalline β-tin (Sn) were conducted at various strain rates (10−3/s, 10−1/s and 1/s) and temperatures (294 K and 193 K) to understand the effects of these variables on the stress–strain response, microstructure evolution, and stress relaxation behavior. Multiple Sn specimens were subjected to complex compressive loading/unloading/reloading paths at different strain rates. Specimens initially compressed at higher strain rates showed strain rate-dependent texture evolution and more pronounced relaxation upon reloading, as compared to those pre-strained at lower rates at room temperature (RT). Compression tests conducted at low temperature (193 K) revealed increased strength, similar to the enhanced strength observed when the strain rate was increased at RT. Neutron diffraction was employed to characterize the initial and final bulk textures of the RT specimens. Electron backscatter diffraction was utilized to examine the crystallographic grain orientation and morphology, thereby identifying the signatures of dislocation-mediated deformation, grain refinement, recrystallization, and twinning behaviors. Elastic-plastic self-consistent simulations were performed to investigate the deformation modes responsible for the strain rate-dependent macroscopic stress–strain response and texture evolution. Effects of crystallographic orientation on stress relaxation behavior was also examined. The model predictions are in reasonable agreement with experimental observations.

Reduced-order particle-in-cell simulations of a high-power magnetically shielded Hall thruster

High-power magnetically shielded Hall thrusters have emerged in recent years to meet the needs of the next-generation on-orbit servicing and exploration missions. Even though a few such thrusters are currently undergoing their late-stage development and qualification campaigns, many unanswered questions yet exist concerning the behavior and evolution of the plasma in these large-size thrusters that feature an unconventional magnetic field topology. Noting the complex, multi-dimensional nature of plasma processes in Hall thrusters, high-fidelity particle-in-cell (PIC) simulations are optimal tools to study the intricate plasma behavior. Nonetheless, the significant computational cost of traditional multi-dimensional PIC schemes renders simulating the high-power thrusters without any physics-altering speed-up factors unfeasible. The novel reduced-order ‘quasi-2D’ PIC scheme enables a significant reduction in the computational cost requirement of the PIC simulations. Thus, in this article, we demonstrate the applicability of the reduced-order PIC for a cost-efficient, self-consistent study of the physics in high-power Hall thrusters by performing simulations of a 20 kW-class magnetically shielded Hall thruster along the axial-azimuthal and radial-azimuthal coordinates. The axial-azimuthal quasi-2D simulations are performed for three operating conditions in a rather simplified representation of the thruster’s inherently 3D configuration. Nevertheless, we have resolved self-consistently an unprecedented 650 µs of the discharge evolution without any ad-hoc electron mobility model, capturing several breathing cycles and approximating the experimental performance parameters with an accuracy of 70%–80% across the operating conditions. The radial-azimuthal simulations, carried out at three cross-sections corresponding to different axial locations within the discharge channel, have casted further light on the evolution of the azimuthal instabilities and the resulting variations in the electrons’ cross-field mobility and the plasma-wall interactions. Particularly, we observed the development of a long-wavelength, relatively low-frequency wave mode near the exit plane of the thruster’s channel that induces a notable electron transport and a significant ion heating.

Chern insulator phases and spontaneous spin and valley order in a moiré lattice model for magic-angle twisted bilayer graphene

At a certain ``magic'' relative twist angle of two graphene sheets it remains a challenge to obtain a detailed description of the proliferation of correlated topological electronic phases and their filling dependence. We perform a self-consistent real-space Hartree-Fock study of an effective moir\'e lattice model to map out the preferred ordered phases as a function of Coulomb interaction strength and moir\'e flat-band filling factor. It is found that a quantum valley Hall phase, previously discovered at charge neutrality, is present at all integer fillings for sufficiently large interactions. However, except for charge neutrality, additional spontaneous spin/valley polarization is present in the ground state at nonzero integer fillings, leading to Chern insulator phases and anomalous quantum Hall effects at odd filling factors, thus constituting an example of interaction-driven nontrivial topology. At weaker interactions, all nonzero integer fillings feature metallic inhomogeneous spin/valley ordered phases which may also break additional point group symmetries of the system. We discuss these findings in the light of previous theoretical studies on and recent experimental developments related to magic-angle twisted bilayer graphene.

Self-Consistent Study of the Superconducting Gap in the Strontium-doped Lanthanum Cuprate

This work is aimed at numerically investigating the behavior of the Fermi energy in Strontium-doped Lanthanum Cuprate, using a numerical zero temperature elastic scattering cross-section procedure in the unitary collision regime. The main task is to vary the zero temperature superconducting energy gap from its zero value in the normal state, to the highest value of 60 meV. We find that there are two different reduced phase space regimes for the first harmonic line node's order parameter. The first one, represented by a Fermi energy with a value of - 0.4 meV, where the rest of the material parameters, and the degrees of freedom of the normal to the superconducting phase transition are not sensitive to the self-consistent variation of the zero temperature superconducting energy gap. A different case is found when in the self-consistent numerical procedure, the Fermi energy takes a value of - 0.04 meV, indicating that the fermion-dressed quasiparticles have material parameters strongly sensitive to the numerical changes in the zero temperature gap, resulting in a reduced phase space, where the input and output zero superconducting energy values, and the degrees of freedom are separated by the self-consistent numerical analysis. The first scenario considers that when the Fermi energy and the nearest hopping terms have the same order of magnitude, the physics can be described by a picture given by nonequilibrium statistical mechanics. A second scenario indicates, that when the Fermi energy parameter and the hopping term have different order of magnitude; the physical picture tends to be related to the nonrelativistic quantum mechanical degrees of freedom coming from quasi-stationary quantum energy levels, with a damping term seen in the probability density distribution function, that is described in the configuration space. Henceforth, it is concluded that the use of the zero temperature elastic scattering cross-section links the phase and configuration spaces through the inverse scattering lifetime, and helps to clarify the role of the degrees of freedom in Strontium-doped Lanthanum Cuprate. Finally, we think that the self-consistent numerical procedure with the reduced phase space, induces nonlocality in the inverse scattering lifetime.

Self-Consistent Study of GaAs/AlGaAs Quantum Wells with Modulated Doping

In this work, the characterization and analysis of the physics of a GaAs quantum well with AlGaAs barriers were carried out, according to an interior doped layer. An analysis of the probability density, the energy spectrum, and the electronic density was performed using the self-consistent method to solve the Schrödinger, Poisson, and charge-neutrality equations. Based on the characterizations, the system response to geometric changes in the well width and to non-geometric changes, such as the position and with of the doped layer as well as the donor density, were reviewed. All second-order differential equations were solved using the finite difference method. Finally, with the obtained wave functions and energies, the optical absorption coefficient and the electromagnetically induced transparency between the first three confined states were calculated. The results showed the possibility of tuning the optical absorption coefficient and the electromagnetically induced transparency via changes to the system geometry and the doped-layer characteristics.

Does the Spin State and Oriented External Electric Field Boost the Efficiency of Fe(II) Pincer Catalyst toward CO2Hydrogenation Reaction?

In this study, we have explored the catalytic reactivities of four PNP-pincer supported Fe(II) complexes, namely, [(iPrPNMeP)FeH2(CO)] (1), [(iPrPNMeP)FeH(CO)(BH4)] (2), [(iPrPNHP)FeH2(CO)] (3), and [(iPrPNMeP)FeH(BH4)] (4) (iPrPNMeP = MeN{CH2CH2(PiPr2)}2 and iPrPNHP = HN{CH2CH2(PiPr2)}2) toward reductive CO2 hydrogenation for formate production. Our density functional theory and ab initio complete active space self-consistent field study have identified three fundamental steps in this catalytic transformation: (i) anchoring of the CO2 molecule in the vicinity of the metal using noncovalent interactions, (ii) catalyst regeneration via H2 cleavage, and (iii) formate rebound step leading to catalytic poisoning. The variations in the catalytic efficiency observed among these catalysts were attributed to either easing of steps (i) and (ii) or the hampering step (iii). This can be achieved in various chemical/non-chemical ways, for instance, (a) incorporation of strong-field ligands such as CO facilitating single-state reactivity and eliminating two-state reactivity that generally enhances the rate and (b) inclusion of Lewis acids such as LiOTf and strong bases found to either avoid catalytic poisoning or ease the H-H cleavages, to enhance the rate of reaction (c) evading mixing of excited open-shell singlet states to the ground closed-shell singlet state that hampers the catalytic regeneration. We have probed the role of oriented external electric fields (OEEFs) in the entire mechanistic profile for the best and worst catalyst, and our study suggests that imposing OEEFs opposite to the reaction axis (z-axis) fastens the catalytic regeneration step and, at the same time, hampers catalytic poisoning. The application of OEEFs is found to regulate the energetics of various spin states and can hamper two-state reactivity, therefore increasing the efficiency. Thus, this study provides insights into the CO2 hydrogenation mechanism where the role of bases/Lewis acid, ligand design, spin states, and electric field in a particular direction has been established and is, therefore, likely to pave the way forward for a new generation of catalysts.

One-dimensional Numerical Study on Ignition of the Helium Envelope in Dynamical Accretion during the Double-degenerate Merger

In order for a double-detonation model to be viable for normal type Ia supernovae, the adverse impact of helium-burning ash on early time observables has to be avoided, which requires that the helium envelope mass should be at most 0.02 M ⊙. Most of the previous studies introduced detonation by artificial hot spots, and therefore the robustness of the spontaneous helium detonation remains uncertain. In the present work, we conduct a self-consistent hydrodynamic study on the spontaneous ignition of the helium envelope in the context of the double-degenerate channel, by applying an idealized one-dimensional model and a simplified seven-isotope reaction network. We explore a wide range of the progenitor conditions and demonstrate that the chance of direct initiation of detonation is limited. Especially, the spontaneous detonation requires the primary envelope mass of ≳0.03 M ⊙. Ignition as deflagration is instead far more likely, which is feasible for the lower envelope mass down to ∼0.01 M ⊙, which might lead to subsequent detonation once the deflagration-to-detonation transition (DDT) is realized. High-resolution multidimensional simulations are required to further investigate the DDT possibility, as well as accurately derive the threshold between the spontaneous detonation and deflagration ignition regimes. Another interesting finding is the effect of the composition: while mixing with the core material enhances detonation as previously suggested, it rather narrows the chance for deflagration due to the slower rate of the 12C(α,γ)16O reaction at the lower temperature ∼108K, with the caveat that we presently neglect the proton-catalyzed reaction sequence of 12C(p,γ)13O(α,p)16O.

Quasiparticle Self-Consistent GW Study of Simple Metals.

The method is a standard method to calculate the electronic band structure from first principles. It has been applied to a large variety of semiconductors and insulators but less often to metallic systems, in particular, with respect to a self-consistent employment of the method. In this work, we take a look at all-electron quasiparticle self-consistent (QS) calculations for simple metals (alkali and alkaline earth metals) based on the full-potential linearized augmented-plane-wave approach and compare the results to single-shot (i.e., non-selfconsistent) calculations, density-functional theory (DFT) calculations in the local-density approximation, and experimental measurements. We show that, while DFT overestimates the bandwidth of most of the materials, the quasiparticle renormalization corrects the bandwidths in the right direction, but a full self-consistent calculation is needed to consistently achieve good agreement with photoemission data. The results mainly confirm the common belief that simple metals can be regarded as nearly free electron gases with weak electronic correlation. The finding is particularly important in light of a recent debate in which this seemingly established view has been contested.

First detection and analysis of an electronic spectrum of vanadium hydride: The D5Π-X5Δ (0,0) band.

The D5Π-X5Δ (0,0) band of vanadium hydride at 654nm has been recorded by laser excitation spectroscopy and represents the first analyzed spectrum of VH in the gas phase. The molecules were generated using a hollow cathode discharge source, with laser-induced fluorescence detected via the D5Π-A5Π (0,0) transition. All five main (ΔΩ = ΔΛ) subbands were observed as well as several satellite ones, which together create a rather complex and overlapped spectrum covering the region 15 180-15 500 cm-1. The D5Π state displays the effects of three strong local perturbations, which are likely caused by interactions with high vibrational levels of the B5Σ- and c3Σ- states, identified in a previous multiconfigurational self-consistent field study by Koseki et al. [J. Phys. Chem. A 108, 4707 (2004)]. Molecular constants describing the X5Δ, A5Π, and D5Π states were determined in three separate least-squares fits using effective Hamiltonians written in a Hund's case (a) basis. The fine structure of the ground state is found to be consistent with its assignment as a σπ2δ, 5Δ electronic state. The fitted values of its first-order spin-orbit and rotational constants in the ground state are A=36.537815cm-1 and B = 5.7579(13)cm-1, the latter of which yields a bond length of R0=1.72122 Å. This experimental value is in good agreement with previous computational studies of the molecule and fits well within the overall trend of decreasing bond length across the series of 3d transition metal monohydrides.

Self-Consistent Study of the Ground State and $$\beta$$-Decay Properties of Oxygen and Fluorine Isotopes

Self-Consistent Study of the Ground State and $$\beta$$-Decay Properties of Oxygen and Fluorine Isotopes

Electron-cyclotron resonance heating and current drive source for flux-driven gyrokinetic simulations of tokamaks

Electromagnetic waves that resonate with the cyclotron motion of electrons in a magnetized plasma can efficiently transfer their momentum and energy to the plasma. This is routinely used to heat or drive current in tokamak plasmas. The impact of this localized source of momentum and energy on turbulence and the retro-action of turbulence on the resonant interaction between the electromagnetic wave and the plasma has been scarcely studied due to the difficulty in self-consistently simulating the two physical mechanisms. In this paper, a realistic source representing electron-cyclotron resonance heating (ECRH) and electron-cyclotron current drive (ECCD) is derived and implemented in a gyrokinetic code. The implementation of this realistic source in any existing global gyrokinetic code would enable the self-consistent study of turbulence in the presence of ECRH/ECCD using this code. The analytical source derived in this paper is valid for a beam propagating in the equatorial plane of an axisymmetric tokamak plasma. The realistic ECRH/ECCD source is implemented in the global gyrokinetic code ORB5 and successfully benchmarked against analytical theory (Albajar et al 2006 Plasma Phys. Control. Fusion 49 15–29) and the C3PO/LUKE suite of codes (Peysson et al 2011 Plasma Phys. Control. Fusion 53 124028), which is routinely used to study ECRH/ECCD deposition.

Self-Consistent Study of Nuclear Charge Radii in Ar–Ti Region

Self-Consistent Study of Nuclear Charge Radii in Ar–Ti Region

Anatomy of Photoevaporation Base: Linking the Property of the Launched Wind to Irradiation Flux

Ultraviolet and X-rays from radiation sources disperse nearby gas clumps by driving winds due to heating associated with the photochemical processes. This dispersal process, photoevaporation, constrains the lifetimes of the parental bodies of stars and planets. To understand this process in a universal picture, we develop an analytical model that describes the fundamental physics in the vicinity of the wind-launching region. The model explicitly links the density and velocity of photoevaporative winds at the launch points to the radiation flux reaching the wind-launching base, using a jump condition. The model gives a natural boundary condition for the wind-emanating points. We compare the analytical model with the results of radiation hydrodynamic simulations, where a protoplanetary disk is irradiated by the stellar extreme-ultraviolet, and confirm good agreement of the base density and velocity, and radial profiles of mass-loss rates. We expect that our analytical model is applicable to other objects subject to photoevaporation not only by extreme-ultraviolet but by far-ultraviolet/X-rays with suitable modifications. Future self-consistent numerical studies can test the applicability.