Body Perturbation Research Articles

Band gap, effective masses, and energy level alignment of 2D and 3D halide perovskites and heterostructures using DFT-1/2

We revisit the Slater half-occupation technique within the DFT-1/2 method to provide improved accuracy of 2D and 3D halide perovskites band gaps at a moderate computational cost. We propose an electron removal scheme from the halide states that drastically improve the predicted band gaps of 2D compounds. Concurrently, we compute the effective masses of the considered structures and show that DFT-1/2 describes them with a nice degree of accuracy when compared to available experimental data. Moreover, we assess the suitability of DFT-1/2 to compute the energy level alignments of this family of compounds. We compare the results in light of those we predict using the hybrid functional HSE06 and the many body perturbation theory within the $G0W0$ approximation. We discuss the limitations of our refined DFT-1/2 scheme, which tends to overestimate the downshift of the absolute valence energy levels of the layered perovskite systems. We anticipate that our results would be useful to initiate benchmark studies and investigate large systems such as heterostructures for which other approaches may be out of reach.

The Role of Predictability of Perturbation in Control of Posture: A Scoping Review.

Efficient maintenance of posture depends on the ability of humans to predict consequences of a perturbation applied to their body. The purpose of this scoping review was to map the literature on the role of predictability of a body perturbation in control of posture. A comprehensive search of MEDLINE, EMBASE, and CINAHL databases was conducted. Inclusion criteria were studies of adults participating in experiments involving body perturbations, reported outcomes of posture and balance control, and studies published in English. Sixty-three studies were selected. The reviewed information resources included the availability of sensory information and the exposure to perturbations in different sequences of perturbation magnitudes or directions. This review revealed that people use explicit and implicit information resources for the prediction of perturbations. Explicit information consists of sensory information related to perturbation properties and timing, whereas implicit information involves learning from repetitive exposures to perturbations of the same properties.

Apparent Motion of the Circumstellar Envelope of CQ Tau in Scattered Light

Abstract The study of spiral structures in protoplanetary disks is of great importance for understanding the processes in the disks, including planet formation. Bright spiral arms were detected in the disk of young star CQ Tau by Uyama et al. in the H and L bands. The spiral arms are located inside the gap in millimeter-sized dust, discovered earlier using Atacama Large Millimeter/submillimeter Array observations. To explain the gap, Ubeira Gabellini et al. proposed the existence of a planet with the semimajor axis of 20 au. We obtained multi-epoch observations of a spiral feature in the circumstellar envelope of CQ Tau in the I c band using a novel technique of differential speckle polarimetry. The observations covering a period from 2015 to 2021 allow us to estimate the pattern speed of the spiral: −0.°2 ± 1.°1 yr−1 (68% credible interval; positive value indicates counterclockwise rotation), assuming a face-on orientation of the disk. This speed is significantly smaller than expected for a companion-induced spiral, if the perturbing body has a semimajor axis of 20 au. We emphasize that the morphology of the spiral structure is likely to be strongly affected by shadows of a misaligned inner disk detected by Eisner et al.

On the Dominant Lunisolar Perturbations for Long-Term Eccentricity Variation: The Case of Molniya Satellite Orbits

The aim of this work is to investigate the main dominant terms of lunisolar perturbations that affect the orbital eccentricity of a Molniya satellite in the long term. From a practical point of view, these variations are important in the context of space situational awareness—for instance, to model the long-term evolution of artificial debris in a highly elliptical orbit or to design a reentry end-of-life strategy for a satellite in a highly elliptical orbit. The study assumes a doubly averaged model including the Earth’s oblateness effect and the lunisolar perturbations up to the third-order expansion. The work presents three important novelties with respect to the literature. First, the perturbing terms are ranked according to their amplitudes and periods. Second, the perturbing bodies are not assumed to move on circular orbits. Third, the lunisolar effect on the precession of the argument of pericenter is analyzed and discussed. As an example of theoretical a application, we depict the phase space description associated with each dominant term, taken as isolated, and we show which terms can apply to the relevant dynamics in the same region.

Enhanced Kozai–Lidov Eccentricity Oscillations in Nuclear Star Clusters

Abstract Stellar motions in the innermost parts of galactic nuclei, where the gravity of a supermassive black hole dominates, follow Keplerian ellipses to the first order of approximation. These orbits may be subject to periodic (Kozai–Lidov) oscillations of their orbital elements if some nonspherically distributed matter (e.g., a secondary massive black hole, coherent stellar subsystem, or large-scale gaseous structure) perturbs the gravity of the central supermassive black hole. These oscillations are, however, affected by the overall potential of the host nuclear star cluster. In this paper, we show that its influence strongly depends on the properties of the particular system, as well as the considered timescale. We demonstrate that for systems with astrophysically relevant parameters, the Kozai–Lidov oscillations of eccentricity can be enhanced by the extended potential of the cluster in terms of reaching significantly higher maximal values. In a more general statistical sense, the oscillations of eccentricity are typically damped. The efficiency of the damping, however, may be small to negligible for the suitable parameters of the system. This applies, in particular, in the case when the perturbing body is on an eccentric orbit.

First-principles correction scheme for linear-response time-dependent density functional theory calculations of core electronic states.

Linear-response time-dependent density functional theory (LR-TDDFT) for core level spectroscopy using standard local functionals suffers from self-interaction error and a lack of orbital relaxation upon creation of the core hole. As a result, LR-TDDFT calculated x-ray absorption near edge structure spectra needed to be shifted along the energy axis to match experimental data. We propose a correction scheme based on many-body perturbation theory to calculate the shift from first-principles. The ionization potential of the core donor state is first computed and then substituted for the corresponding Kohn-Sham orbital energy, thus emulating Koopmans's condition. Both self-interaction error and orbital relaxation are taken into account. The method exploits the localized nature of core states for efficiency and integrates seamlessly in our previous implementation of core level LR-TDDFT, yielding corrected spectra in a single calculation. We benchmark the correction scheme on molecules at the K- and L-edges as well as for core binding energies and report accuracies comparable to higher order methods. We also demonstrate applicability in large and extended systems and discuss efficient approximations.

Exploring Exciton and Polaron Dominated Photophysical Phenomena in Ruddlesden-Popper Phases of Ban+1ZrnS3n+1 (n = 1-3) from Many Body Perturbation Theory.

Ruddlesden-Popper (RP) phases of Ban+1ZrnS3n+1 are an evolving class of chalcogenide perovskites in the field of optoelectronics, especially in solar cells. However, detailed studies regarding its optical, excitonic, polaronic, and transport properties are hitherto unknown. Here, we have explored the excitonic and polaronic effect using several first-principles based methodologies under the framework of Many Body Perturbation Theory. Unlike its bulk counterpart, the optical and excitonic anisotropy are observed in Ban+1ZrnS3n+1 (n = 1-3) RP phases. As per the Wannier-Mott approach, the ionic contribution to the dielectric constant is important, but it gets decreased on increasing n in Ban+1ZrnS3n+1. The exciton binding energy is found to be dependent on the presence of large electron-phonon coupling. We further observed maximum charge carrier mobility in the Ba2ZrS4 phase. As per our analysis, the optical phonon modes are observed to dominate the acoustic phonon modes, leading to a decrease in polaron mobility on increasing n in Ban+1ZrnS3n+1 (n = 1-3).

The cosmology dependence of galaxy clustering and lensing from a hybrid N-body–perturbation theory model

ABSTRACT We implement a model for the two-point statistics of biased tracers that combines dark matter dynamics from N-body simulations with an analytic Lagrangian bias expansion. Using Aemulus, a suite of N-body simulations built for emulation of cosmological observables, we emulate the cosmology dependence of these non-linear spectra from redshifts z = 0 to z = 2. We quantify the accuracy of our emulation procedure, which is sub-per cent at $k=1\, h \,{\rm Mpc}^{-1}$ for the redshifts probed by upcoming surveys and improves at higher redshifts. We demonstrate its ability to describe the statistics of complex tracer samples, including those with assembly bias and baryonic effects, reliably fitting the clustering and lensing statistics of such samples at redshift z ≃ 0.4 to scales of $k_{\rm max} \approx 0.6\, h\,\mathrm{Mpc}^{-1}$. We show that the emulator can be used for unbiased cosmological parameter inference in simulated joint clustering and galaxy–galaxy lensing analyses with data drawn from an independent N-body simulation. These results indicate that our emulator is a promising tool that can be readily applied to the analysis of current and upcoming data sets from galaxy surveys.

Analysis of Celestial Gravity Influence on Heliocentric Formation Flying of Gravitational Wave Observatory

A mathematical model of celestial gravity influence on heliocentric formation flying of gravitational wave observatory is established for Taiji in this paper. Influences of planets, the Moon, dwarf planets and asteroids in the solar system on heliocentric formation flying of gravitational wave observatory are analyzed by simulation. To analyze the influence of asteroids on the stability of constellation, a double screening method is proposed, which takes the orbit distance and magnitude of asteroids into consideration comprehensively. The method avoids a large number of calculations on asteroids and is able to quickly estimate the influence of the relative acceleration of asteroids on constellation. The influences of initial phase angles on heliocentric formation-flying satellites are also analyzed. Simulation results show that the Earth, the Venus and the Jupiter have great influences on heliocentric formation flying of gravitational wave observatory, and their cumulated relative acceleration is -2.78×10^-11 km·s^-2. The relative acceleration caused by dwarf is 1.25×10^-17 km·s^-2. The relative acceleration caused by asteroids is 1.1180×10^-15 km·s^-2. Moreover, influences of gravity perturbations of solar system bodies on formation-flying satellites are insensitive to initial phase angles.

Multiconfiguration Dirac–Hartree–Fock energy levels, weighted oscillator strengths, transitions probabilities, lifetimes, hyperfine interaction constants, Landé g-factors and isotope shifts of O VII

Energy levels, weighted oscillator strengths and transition probabilities, lifetimes, hyperfine interaction constants, Landé gJ factors and isotope shifts have been calculated for all levels of 1s2 and 1snl (n=2-8,l⩽7) configurations of He-like oxygen ion (O VII). The calculations were performed using the Multiconfigurational Dirac-Hartree–Fock (MCDHF) and the Relativistic Configuration Interaction (RCI) methods. A second set of calculations was obtained with the Many Body Perturbation Theory (MBPT) method. Transition probabilities are reported for all E1,E2,M1 and M2 transitions. Breit interactions and quantum electrodynamics effects were included in the RCI calculations. Comparisons have been made with the compiled data from the NIST ASD and other calculations and a good agreement was found which confirms the reliability of our results. The accuracy of the present calculations is high enough to facilitate identification of many observed spectral lines. For the first time, we present some missing data for the He-like oxygen ion.

Phasing Maneuver Analysis from a Low Lunar Orbit to a Near Rectilinear Halo Orbit

The paper describes the preliminary design of a phasing trajectory in a cislunar environment, where the third body perturbation is considered non-negligible. The working framework is the one proposed by the ESA’s Heracles mission in which a passive target station is in a Near Rectilinear Halo Orbit and an active vehicle must reach that orbit to start a rendezvous procedure. In this scenario the authors examine three different ways to design such phasing maneuver under the circular restricted three-body problem hypotheses: Lambert/differential correction, Hohmann/differential correction and optimization. The three approaches are compared in terms of ΔV consumption, accuracy and time of flight. The selected solution is also validated under the more accurate restricted elliptic three-body problem hypothesis.

Energy levels, transition rates, lifetimes of He-like-ions with [formula omitted] deduced from relativistic multiconfiguration Dirac–Hartree–Fock and many body perturbation theory calculations

We disclose relativistic multiconfiguration Dirac–Hartree–Fock (MCDHF) spectrum calculations for He-like-ions with Z=72–76. The excitation energy and the oscillator strength values have been computed for the 127 odd- and even-parity states as well as lifetimes and transition rates between different states. To study the accuracy of our results, we have implemented parallel calculations using a Flexible Atomic Code (FAC) by introducing the many body perturbation theory (MBPT). Additionally, the Breit interaction and leading quantum electrodynamics effects (QED) are included as perturbations in the present calculations.

Numerical-Analytical Study of Linked Orbits in the Restricted Elliptic Doubly Averaged Three-Body Problem

The restricted elliptic doubly averaged three-body problem is considered. The terms up to the second order inclusive with respect to the orbital eccentricity of the perturbing body are retained in the expansion of the perturbing function. The elements of the elliptical orbit for the perturbed body are deemed arbitrary. The special, so-called linked orbits of a negligible-mass body are investigated by numerically integrating the averaged equations in Keplerian elements. For such orbits the points of their intersection with the orbital plane of the perturbing body are on different sides of this orbit. The evolution of hypothetical and some real cometary orbits is described in the simplest Sun-Jupiter-comet model; their differences from the corresponding orbits in the circular problem have been revealed.

Determining the Structure-Property Relationships of Quasi-Two-Dimensional Semiconductor Nanoplatelets.

We report a theoretical study of CdSe nanoplatelets aimed at identifying the main factors determining their photophysical properties. Using atomic configurations optimized with density functional theory calculations, we computed quasiparticle and exciton binding energies of nanoplatelets with two to seven monolayers. We employed many body perturbation theory at the GW level and solved the Bethe-Salpeter equation to obtain absorption spectra and excitonic properties. Our results, which agree well with recent experiments, were then used to design a model that allows us to disentangle the effects of quantum confinement, strain induced by passivating ligands, and dielectric environment on the electronic properties of nanoplatelets. We found that, for the model to accurately reproduce our first principle results, it is critical to account for surface stress and consider a finite potential barrier and energy-dependent effective masses when describing quantum confinement. Our findings call into question previous assumptions on the validity of an infinite barrier to describe carrier confinement in nanoplatelets, suggesting that it may be possible to optimize interfacial charge transfer and extraction by appropriately choosing passivating ligands. The model developed here is generalizable to core-shell platelets and enables the description of system sizes not yet directly treatable by first-principles calculations.

Sublattice mixing in Cs2AgInCl6 for enhanced optical properties from first-principles

Lead-free double perovskite materials (viz., Cs2AgInCl6) are being explored as stable and nontoxic alternatives of lead halide perovskites. In order to expand the optical response of Cs2AgInCl6 in the visible region, we report here on the stability, electronic structure, and optical properties of Cs2AgInCl6 by sublattice mixing of various elements. We have employed a hierarchical first-principles-based approach starting from density functional theory (DFT) with appropriate exchange-correlation functionals to beyond DFT methods under the framework of many body perturbation theory (viz., G0W0@HSE06). We have started with 32 primary set of combinations of metals M(I), M(II), M(III), and halogen X at Ag/In and Cl sites, respectively, where the concentration of each set is varied to build a database of nearly 140 combinations. The most suitable mixed sublattices are identified to engineer the bandgap of Cs2AgInCl6 to have its application in optoelectronic devices under visible light.

Long-term evolution of orbital inclination due to third-body inclination

The effects of third-body perturbations on natural and artificial satellite orbits have been studied extensively. However, much less attention has been given to the case considering the orbital inclination of the third body. In this paper, it is shown that a perturbed orbit, even with a small initial inclination—much less than the critical Kozai inclination of 39.23 degrees—may significantly increase its inclination due to the inclination of the third-body’s orbit. To study this phenomenon, a new method for finding the inclination of the perturbed body is proposed based on a coordinate transformation. This enables the derivation of an analytical solution for the orbital inclination, predicting the long-term evolution thereof when the third body’s orbit is inclined. It is found that the amplitude of the inclination depends on the inclination of the third body, and on the relative angle between the orbital planes of the perturbed orbiter and the perturbing body. Numerical simulations illustrate the accuracy of the proposed methodology for predicting the long-term evolution of the orbital inclination.

MoS2 and Janus (MoSSe) based 2D van der Waals heterostructures: emerging direct Z-scheme photocatalysts.

Two-dimensional (2D) materials, viz. transition metal dichalcogenides (TMD) and transition metal oxides (TMO), offer a platform that allows the creation of heterostructures with a variety of properties. The optoelectronic industry has observed an upheaval in the research arena of MoS2 based van der Waals (vdW) heterostructures (HTSs) and Janus structures. Therefore, interest towards these structures is backed by the ability to select their electronic and optical properties. The present study investigates the photocatalytic abilites of bilayer, MoS2 and Janus (MoSSe) based vdW HTSs, viz. MoS2/TMO, MoS2/TMD, MoSSe/TMO and MoSSe/TMD, by a first-principles based approach under the framework of (hybrid) density functional theory (DFT) and many body perturbation theory (GW approximation). We have considered HfS2, ZrS2, TiS2 and WS2, and HfO2, T-SnO2 and T-PtO2 from the families of TMDs and TMOs, respectively. The photocatalytic properties of these vdW HTSs are thoroughly investigated and compared with their respective individual monolayers by visualizing their band edge alignments, electron–hole recombination and optical properties. Strikingly, we observe that, despite most of the individual monolayers not performing optimally as photocatalysts, type II band edge alignment is noticed in vdW HTSs and they appear to be efficient photocatalysts via the Z-scheme. Moreover, these vdW HTSs have also shown promising optical responses in the visible region. Finally, electron–hole recombination, H2O adsorption and hydrogen evolution reaction (HER) results establish that MoSSe/HfS2, MoSSe/TiS2, MoS2/T-SnO2 and MoSSe/ZrS2 are probable highly efficient Z-scheme photocatalysts.

Physically inspired deep learning of molecular excitations and photoemission spectra.

Modern functional materials consist of large molecular building blocks with significant chemical complexity which limits spectroscopic property prediction with accurate first-principles methods. Consequently, a targeted design of materials with tailored optoelectronic properties by high-throughput screening is bound to fail without efficient methods to predict molecular excited-state properties across chemical space. In this work, we present a deep neural network that predicts charged quasiparticle excitations for large and complex organic molecules with a rich elemental diversity and a size well out of reach of accurate many body perturbation theory calculations. The model exploits the fundamental underlying physics of molecular resonances as eigenvalues of a latent Hamiltonian matrix and is thus able to accurately describe multiple resonances simultaneously. The performance of this model is demonstrated for a range of organic molecules across chemical composition space and configuration space. We further showcase the model capabilities by predicting photoemission spectra at the level of the GW approximation for previously unseen conjugated molecules.

An automatic tree search algorithm for the Tisserand graph

The Tisserand graph (TG) is a graphical tool commonly employed in the preliminary design of gravity-assisted trajectories. The TG is a two-dimensional map showing essential orbital information regarding the Keplerian orbits resulting from the close passage by one or more massive bodies, given the magnitude of the hyperbolic excess speed (v∞) and the minimum allowed pericenter height for each passage. Contours of constant v∞ populate the TG. Intersections between contours allow to link consecutive flybys and build sequences of encounters en route to a selected destination. When the number of perturbing bodies is large and many v∞ levels are considered, the identification of all the possible sequences of encounters through visual inspection of the TG becomes a laborious task. Besides, if the sequences are used as input for a numerical code for trajectory design and optimization, an automated examination of the TG is desirable. This contribution describes an automatic technique to explore the TG and find all the encounter paths. The technique is based on a tree search method, and the intersections between contours are computed using the regula-falsi scheme. The method is validated through comparisons with solutions available in the open literature. Examples are given of application to interplanetary mission scenarios, including the coupling with a trajectory optimizer.

Analysis of Physiological Signals of Individuals with Eyes Closed Subjected to Unexpected Direction-Specific Stimuli Causing Instability

Research regarding the cerebral cortex and muscle activity patterns of the body used for postural balance control when sudden instability stimuli occur is lacking. This study analyzed individuals' physiological signals when direction-specific instability stimuli were applied while their eyes were closed. Healthy adults in their 20s maintained their postural balance while looking at the center of gravity provided by a monitor with a three-dimensional dynamic postural balance training system. We performed electroencephalography (EEG) and measured trunk and lower extremity muscle activity of participants with their eyes closed when subjected to four direction-specific instability stimuli (anterior, posterior, left, and right). EEG results showed that gamma waves increased significantly with an unbalanced stimulus when the participant's eyes were open and closed. The increased gamma wave rate with eyes closed was low in the exercise planning area, where information is relatively integrated and exercise is planned without visual information. EMG results showed fewer gamma waves on EEG due to the low focus on postural control because participants could not observe the center of gravity, which is the basis for balance. The trunk and lower extremity muscles tended to be used more due to the larger body perturbation angle. These outcomes can be used as basic data regarding how the human brain and muscles maintain postural balance when an unexpected external instability stimulus occurs. Quantitative postural balance rehabilitation training protocols for the elderly and those with disabilities can be created based on these outcomes.