Cutoff Energy Research Articles

Lifetime mapping using femtosecond time-resolved photoemission electron microscopy.

Time-resolved photoemission electron microscopy (PEEM) has established itself as a versatile experimental technique to unravel the ultrafast electron dynamics of materials with nanometer-scale resolution. However, the approach of performing PEEM-based, pixel-by-pixel lifetime mapping has not been reported thus far. Herein, we describe in detail the data pre-processing procedure and an algorithm to perform time-trace fittings of each pixel. We impose an energy cutoff for each pixel prior to spectral integration to enhance the robustness of our approach. With the energy cutoff, the energy-integrated time traces show improved statistics and lower fitting errors, thus resulting in a more accurate determination of the fit parameters, e.g., decay time constants. Our work allows us to reliably construct PEEM-based lifetime maps, which potentially shed light on the effects of local microenvironment on the ultrafast processes of the material and allow spatial distributions of lifetimes to be correlated with observables obtained from complementary microscopic techniques, hence enabling a more comprehensive characterization of the material.

All-optical method for generating transient microstructured targets in laser ion acceleration

We demonstrate an all-optical method that online produces “microstructured” targets by manipulating a Laguerre-Gaussian (LG) prepulse. Besides the enhancement of the proton number, the cutoff energy is nearly doubled. Such transient “microstructured” targets are characterized using both offline and online approaches. Based on probe experiments and hydrodynamic simulations, we develop a simple model to describe the electron density distribution upon the arrival of the main pulse. Two-dimensional particle-in-cell simulations reveal that the annular plasma acts as an oscillating cavity for hot electrons and results in a cascaded acceleration effect. The combination of low-intensity LG prepulses and ultraintense Gaussian pulses opens another avenue for fine-tuning laser-plasma interactions spatiotemporally in interdisciplinary applications. Published by the American Physical Society 2024

High-pressure phase transitions of series of catenated nitrogen energetic crystals Nx (x = 4, 8, 10): A comparative DFT-D study.

High-pressure chemistry has advantages in exploring novel energetic materials and is the key to the development of new high-energy materials. The complexity and danger of experimental processes require a deeper understanding by advanced simulation techniques. Therefore, a high-precision comparative DFT-D study was performed to investigate the effect of pressure on series of catenated nitrogen energetic crystals. The results show that there exist phase transitions for N4, N8, and N10 at 4 GPa, 3 GPa, and 2 GPa respectively, which are embodied in various properties of these crystals. Studies on band gap and DOS indicate pressure-induced improvement on the ability for electrons transition from occupied orbitals to empty ones. Hirshfeld surface analysis qualitatively suggests that hydrogen bonding interactions are becoming dominant inter-molecular interactions. The topological analysis quantitatively reveals that pressure is beneficial to enhancing the inter-molecular hydrogen bonding energy, thereby playing an important role in the stability of high-pressure phases. The discussions on mechanical properties imply that pressure can improve the rigidity of these energetic systems and enhance their mechanical properties. Our findings evidence the high-pressure phase transitions for catenated nitrogen energetic crystals, which lay the theoretical foundation for the development of novel energetic materials. Series of catenated nitrogen energetic crystals N4, N8 and N10 were obtained from experiments. Optimizations were performed by GGA/PBE functional and G06 dispersion correction within the framework of CASTEP code, and the cutoff energies of the plane waves were set to 700 eV. The particular moiety in the crystals was extracted by Multiwfn 3.6 and subsequent analysis was conducted by Gaussian 09W package.

CALCULATION OF ELECTRONIC PROPERTIES OF LiBX3 (B = Pb AND Sn; X = Br, Cl AND I) CUBIC PHASE BY DENSITY FUNCTIONAL THEORY

Perovskite solar cells utilize perovskite as the active material to convert sunlight into electrical energy. Perovskite is a compound with a crystal structure of ABX₃, where A and B are cations, and X is an anion, usually a halide. Research continues to find perovskites with high efficiency. This efficiency is related to the electronic structure, which can be analyzed using Density Functional Theory (DFT). In this study, the electronic structure of cubic phase LiBX₃ perovskites (B = Pb and Sn; X = Br, Cl, and I) is investigated using Quantum ESPRESSO software. Various parameters such as cut-off energy, k-points, and lattice constants were modified to obtain optimal values. From the optimization results, the band gap, DOS, and PDOS values for the six perovskites were obtained. The resulting band gap energy (Eg) are LiPbBr₃ at 1,71 eV, LiPbCl₃ at 1,87 eV, LiPbI₃ at 1,43 eV, LiSnBr₃ at 0,51 eV, LiSnCl₃ at 0,65 eV, and LiSnI₃ at 0,28 eV. These results show that the band gap energy values increase with the change in atomic radius from Sn to Pb and decrease with the change in atomic radius from Cl, Br to I. The electronic structure calculations of LiBX₃ (B = Pb and Sn; X = Br, Cl, and I) show semiconductor properties that have the potential to be used as light-absorbing materials in perovskite solar cells. This study states that LiBX₃ has great potential in solar cell applications and offers a deep understanding of the relationship between crystal structure and its electronic properties.

Fast neutron generation with few-cycle, relativistic laser pulses at 1 Hz repetition rate

Laser-driven deuterons generate neutrons with a mean energy of 2.5 MeV, through the 2H(d,n) fusion reaction in a deuterated polyethylene (dPE) tablet. The deuterium ions are accelerated by 12 fs, 21 mJ laser pulses interacting with a 0.2 µm thin dPE foil at a peak intensity of 1018 W/cm2. The laser was operated at 1 Hz repetition rate in bursts of 75 shots. The interaction was characterized and recorded for each laser shot. The ion spectra were measured in the forward and backward directions by Thomson ion spectrometers. Neutron events were detected by a time-of-flight (ToF) system consisting of four plastic scintillators positioned at various angles around the experimental chamber. The maximum cut-off energy of the forward accelerated protons and deuterons was close to 1.4 MeV and 1 MeV, while the mean values are 428 ± 63 keV and 433 ± 80 keV, respectively. Analysis of ToF distributions from 3128 shots resulted in an average yield of 1142 ± 59 neutrons per shot in the energy range of 1.5–4 MeV. The energy distribution of forward-directed neutrons peaks between 3 and 3.5 MeV. Angular dependence analysis showed a perpendicular minimum and a maximum along the deuteron beam, consistent with the expected distribution from the literature and our simulation results.

Proof-of-principle experiment on quasi-phase matching of high-order harmonic generation via the selected-zoning method with a transverse disruptive pulse

We demonstrate the proof-of-principle experiment on all-optical quasi-phase matching (QPM) of high-order harmonic generation (HHG) via the transverse selective-zoning method. The dephasing length and the out-of-phase region in the interacting medium are identified in advance by applying a tomographic diagnosis of the generation process. Then a transverse disruptive pulse is employed to suppress the harmonic emission in the out-of-phase region to achieve QPM. The final output is enhanced by 35% with just one QPM zone. This proof-of-principle result provides the feasibility of ion-based HHG for higher cut-off energies, where phase matching is difficult to achieve.

Characterization of the Western Pictor A Hotspot in Hard X-Rays with NuSTAR

The origin of X-ray emission from the resolved kiloparsec-scale jets and hotspots of many active galactic nuclei remains uncertain, particularly where the X-ray emission is separate from the radio-optical synchrotron component. Possible explanations include synchrotron emission from a second electron population and external Compton or synchrotron self-Compton processes—alternatives which imply very different physical conditions within the jet. Until recently, X-ray studies of resolved jets and hotspots have been restricted to below ∼10 keV, often showing a hard spectral index indicating a spectral peak beyond this energy range. Here we present NuSTAR observations of the nearby powerful radio galaxy Pictor A, in which we clearly detect the western hotspot at approximately 4′ from the host galaxy, the most significant detection of hotspot emission above 10 keV to date. The NuSTAR spectrum is best fit by a single power law of index Γ = 2.03 ± 0.04; an exponential cutoff gives a 1σ lower limit on the cutoff energy of 40.7 keV. We confirm previous findings of variations in the soft X-ray flux detected by Chandra over the 2000 to 2015 period, at a significance of 6.5σ. This rises to >8σ in the common 3–8 keV band using the combined 22 yr span of Chandra and NuSTAR observations. The variability of the western Pictor A hotspot strongly confirms the previously argued synchrotron nature of the X-ray emission for the hotspot, while the lower bound to the spectral cutoff energy implies electron energies in the hotspot reach up to at least a few TeV.

NuSTAR Observation of the TeV-detected Radio Galaxy 3C 264: Core Emission and the Hot Accretion Flow Contribution

3C 264 is one of the few FRI radio galaxies with detected TeV emission. It is a low-luminosity active galactic nucleus (LLAGN) and is generally associated with a radiatively inefficient accretion flow (RIAF). Earlier multiwavelength studies suggest that the X-ray emission originates from a jet. However, the possibility that the RIAF can significantly contribute to the X-rays cannot be ruled out. In particular, hard X-ray emission ≳10 keV has never been detected, making it challenging to distinguish between X-ray models. Here we report a NuSTAR detection up to 25 keV from 3C 264. We also present subpixel deconvolved Chandra images to resolve jet emission down to ∼0.″2 from the center of the unresolved X-ray core. Together with a simultaneous Swift observation, we have constrained the dominant hard X-ray emission to be from its unresolved X-ray core, presumably in its quiescent state. We found evidence of a cutoff in the energy around 20 keV, indicating that at least some of the X-rays from the core can be attributed to the RIAF. The Comptonization model suggests an electron temperature of about 15 keV and an optical depth ranging between 4 and 7, following the universality of coronal properties of black hole accretion. The cutoff energy or electron temperature of 3C 264 is the lowest among those of other LLAGNs. The detected hard X-ray emission is at least an order of magnitude higher than that predicted by synchrotron self-Compton models introduced to explain γ-ray and TeV emission, suggesting that the synchrotron electrons might be accelerated to higher energies than previously thought.

Proton Predominance At UHE Cosmic Rays Through Analysis Of Different Mass Composition Models

Recently, detection of giant (1017 to 1020eV ) and super giant ( Ep >1020 eV ) air showers is gaining importance as the investigation of EAS in these energy ranges is expected to give necessary information on characteristics of high energy nuclear interactions in one hand and for solving the astrophysical problem of Cosmic Ray origin , beyond the Greisen-Zatsepin-Kuzmin cut-off energy near 1020 eV. Due to the very low Cosmic Ray flux in the UHE range ( > 1017 eV ) direct measurement by balloons or satellites are not possible. The experimental approach realized conventionally uses extended ground-based installations catching data of the induced air showers . An alternative approach is to use a low cost particle detector array called mini-array for detecting UHE cosmic rays by Linsley’s method of arrival time measurement. The miniarray consist of eight plastic scintillation counters covering an area of 2m2 operating for detecting EAS particles of primary energy 1017 -1018 eV based on Linsley’s method of arrival time measurement. An optical detector (5 inch diameter PMT) has been installed at the centre of the miniarray to record the associated optical Cerenkov pulse produced by the ultra-relativistic shower particles in the atmosphere with an aim to derive primary mass composition above 1017 eV. Optical pulses are recorded in one channel of the DSO and the stored data in the wave form memory are transferred to the computer via GPIB interface. The particle detector pulses are triggered with the help of trigger circuit and recorded through other channel of the DSO and transferred to the same DSO. However, the data are subjected to large fluctuation both in particle detection and optical photon detection. Primary energy is estimated through the parameter shower size which is also indirectly measured from a small sample of shower front using miniarray data. Mass composition estimated indirectly relies on simulation model. On the basis of pulse height distribution measurement, the inferred mass composition is predominantly protons, with a tendency of mass composition becoming lighter at the highest energies.

Excited-State Forces with the Gaussian and Augmented Plane Wave Method for the Tamm-Dancoff Approximation of Time-Dependent Density Functional Theory.

Augmented plane wave methods enable an efficient description of atom-centered or localized features of the electronic density, circumventing high energy cutoffs and thus prohibitive computational costs of pure plane wave formulations. To complement existing implementations for ground-state properties and excitation energies, we present the extension of the Gaussian and augmented plane wave method to excited-state nuclear gradients within the Tamm-Dancoff approximation of time-dependent density functional theory and its implementation in the CP2K program package. Benchmarks for a test set of 35 small molecules demonstrate that maximum errors in the nuclear forces for excited states of singlet and triplet spin multiplicity are smaller than 0.1 eV/Å. The method is furthermore applied to the calculation of the zero-phonon line of defective hexagonal boron nitride. This spectral feature is reproduced with an error of 0.6 eV in comparison to GW-Bethe-Salpeter reference computations and 0.4 eV in comparison to experimental measurements. Accuracy assessments and applications thus demonstrate the potential use of the outlined developments for large-scale applications on excited-state properties of extended systems.

Reducing the Cost of TD-CI Simulations of Strong Field Ionization.

Strong field ionization of molecules by intense laser pulses can be simulated by time-dependent configuration interaction (TD-CI) with a complex absorbing potential (CAP). Standard molecular basis sets need to be augmented with several sets of diffuse functions for effective interaction with the CAP. This dramatically increases the number of configurations and the cost of the TD-CI simulations as the size of the molecules increases. The cost can be reduced by making use of spin symmetry and by employing an orbital energy cutoff to limit the number of virtual orbitals used to construct the excited configurations. Greater reductions in the number of virtual orbitals can be obtained by examining their interaction with the absorbing potential during simulations and their contributions to the strong field ionization rate. This can be determined from the matrix elements of the absorbing potential and the TD-CI coefficients from test simulations. Compared to a simple 3 hartree cutoff in the orbital energies, these approaches reduce the number of virtual orbitals by 20-35% for neutral molecules and 5-10% for cations. As a result, the cost of simulations is reduced by 35-60% for neutral molecules. The number of virtual orbitals needed can also be estimated by second-order perturbation theory without the need for test simulations. The number of virtual orbitals can be reduced further by adapting orbitals to the laser field using natural orbitals derived from test simulations. This is particularly effective for cations, yielding reductions of more than 20%.

Theoretical study of adsorption of gas (CO, CO2, NH3) by metal (Au, Ag, Cu)-doped single-layer WS2.

The adsorptions of gas (CO, CO2, NH3) by metal (Au, Ag, Cu)-doped single layer WS2 are studied by density functional theory. The doping of metal atoms makes WS2 behave as n-type semiconductors. The final adsorption sites for CO, CO2, and NH3 are close to the atomic sites of the doped metal. The adsorptions of CO and NH3 gases on Cu/WS2, Ag/WS2, and Au/WS2 are dominated by chemisorption. The doped metal atoms enhance the hybridization of the substrate with the gas molecular orbitals, which contributes to the charge transfer and enhances the adsorption of the gas with the material surface. The adsorptions of CO and NH3 on Cu/WS2 and Ag/WS2 allow favorable desorption in a short time after heating. The single-layer Cu/WS2 is proved to have the potential to be used as a reliable recyclable sensor for CO. This work provides a theoretical basis for developing high-performance WS2-based gas sensors. In this paper, the adsorption energy, electronic structure, charge transfer, and recovery time of CO, CO2, and NH3 in the doped system have been investigated based on the CASTEP code of density functional theory. The exchange correlation function used is the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA). The TS (Tkatchenko-Scheffler) dispersion correction method was used to involve the effects of van der Waals interaction on the adsorption energies for all adsorption system. The ultrasoft pseudopotentials are chosen and the plane-wave cut-off energies are set to 500eV. The k-point mesh generated by the Monkhorst package scheme is used to perform the numerical integration of the Brillouin zone and 5 × 5 × 1k-point grid is used. The tolerances of total energy convergence, maximum ionic force, ionic displacement, and stress component are 1.0 × 10-5eV/atom, 0.03eV/Å, 0.001Å, and 0.05 GPa, respectively.

The incident photons cut-off energy, the optical linear equations and the electron phonon interactions in ZnO thin films annealed at different temperatures

The using RF-magnetron sputtering, the ZnO thin films were deposited on glass substrates at room temperature. Then using an electrical furnace in the presence of argon gas, they were annealed at different temperatures (400–600 °C). It was found that with taking Nc = 4, Za = 2, Ne = 8 for ZnO films for covalently bonded crystalline and amorphous chalcogenides, the constant β has values of about 0.37 ± 0.04 and for halides and most oxides that have ionic structure the constant β has values of about 0.26 ± 0.04 eV. It can be seen that with increasing annealing temperature absorption edge these films have a shifting behavior towards larger wavelength. Due to shifting behavior of defects distribution of atoms into films, the values of the cut-off energy, E cut-off and the λ cut-off of these films were about 3.48 eV and 355 nm, respectively. The ZnO films annealed at 500 °C specially above 3 eV have maximum value of optical density. The different linears fitting of ln (⍺) for films were obtained as y = Ex + F where 10<E < 12.5 and 14<F < 16. The ZnO films annealed at 600 °C have minimum value of electron phonon interaction (Ee-p) in a bout of 0.858 eV. The optical band gap and disordering energy plots of these films can be fitted by linear relationship EU and Eg = 0.0989–0.148 EU. We found that as deposited ZnO films have minimum value of steepness parameter σ in about of 30.93 × 10 −2eV.

The effect of strain effect on WS2 monolayer as a potential delivery carrier for anti-myocardial infarction drug: First-principles study.

Myocardial infarction is one of the major health challenges. It is of great significance to develop potential delivery carriers for new anti-myocardial infarction drugs. In this paper, based on first-principles calculations, monolayer WS2 with excellent photoelectric properties was verified as a carrier for the anti-myocardial infarction drug amiodarone (AMD). Studies have shown that the WS2-adsorbed AMD system (WS2@AMD) maintains structural stability and produces an adsorption energy of-2.12 eV. Mulliken charge analysis shows that electrons are transferred from WS2 atoms to AMD atoms. Among them, C, N and O obtained the maximum values of 0.51,0.37 and 0.56 e electrons, respectively, while H and I lost the maximum values of 0.32 and 0.24 e electrons, respectively. The optical response of WS2 adsorbed AMD system is similar to that of WS2. The light absorption coefficients of the two materials in the near ultraviolet region and the visible region can reach the order of 105 cm-1 and 104 cm-1, and the strain makes the light absorption peak red-shifted. The feasibility of temperature-controlled release mechanism of WS2 as AMD carrier was discussed. This theoretical work helps to improve the performance of two-dimensional nanomaterials and make them better as drug delivery carriers to improve the therapeutic effect of myocardial infarction. These results indicate that the WS2 monolayer has potential applications in the development of drug delivery carriers. In this study, based on first-principles calculations, the CASTEP simulation software package was used to study the structure and properties of materials. The interaction between electrons and ions is considered by using Ultrasoft pseudopotentials. In order to eliminate the spurious interaction between adjacent structures caused by periodic calculations, a vacuum space no less than 18 Å is placed in the vertical direction if necessary. Different functions may produce different density functional calculation results. Due to the low sensitivity of the crystal structure to the calculation details, the PBE functional under the generalized gradient approximation (GGA) was initially used for structural optimization, and the energy cutoff value was set to 500 eV. Grimme 's dispersion correction was used to make the results more accurate. The Brillouin zone (BZ) is sampled by a 7 × 7 × 1 K-point grid to ensure the reliability of the original lattice calculation. The lattice vector and atomic coordinates are relaxed, and the tolerance of each atom is less than 0.01 eV/Å. The energy tolerance at the atomic position is less than 10-7 eV/atom. When calculating the band gap, the HSE06 hybrid functional is used to modify the optimized structure of the PBE functional to obtain more accurate results. Spin-polarized DFT calculations were performed to calculate the electronic structure.

First-principle calculations of the electronic, vibrational, and thermodynamic properties of nitrogen-rich salt of 3,6-dinitramino-1,2,4,5-tetrazine [(NH4)2(DNAT)

Energy-containing materials such as explosives have attracted considerable interest recently. In the field of high-energy materials, tetrazine and its derivatives can largely meet the requirements of high nitrogen content and oxygen balance. Nitrogen-rich energetic salts are important research subjects. Nitrogen-rich salt of 3,6-dinitramino-1,2,4,5-tetrazine is a high-energy nitrogen-rich material, but there are few related studies. This paper systematically studies the crystal structure and electronic, vibrational, and thermodynamic properties of (NH4)2(DNAT). The lattice parameters of (NH4)2(DNAT) are observed to align well with the experimental values. The properties of electrons are analyzed by band structure and density of states (DOS). The phonon dispersion curves indicate that the compound is dynamically stable. The vibrational modes of bonds and chemical groups are described in detail, and the peaks in the Raman and infrared spectra are assigned to different vibration modes. Based on the vibration characteristics, thermodynamic properties such as enthalpy (H), Helmholtz free energy (F), entropy (S), Gibbs free energy (G), constant volume heat capacity (CV), and Debye temperature (Θ) are analyzed. This article can pave the way for subsequent work or provide data support to other researchers, promoting further research. In this study, we utilized the density functional theory (DFT) for our calculations. The exchange-correlation potential and van der Waals interactions were characterized based on the GGA-PBE + G function calculation. We obtained Brillouin zone integrals using Monkhorst-Pack k-point grids, with the k-point of the Brillouin zone set to a 2 × 2 × 2 grid. During the self-consistent field operation, we set the total energy convergence tolerance to 5 × 10-6eV per atom. The cut-off energy for the calculation was established at 830eV. Additionally, the states of H (1s1), C (2s2 2p2), N (2s2 2p3), and O (2s2 2p4) were treated as valence electrons in our study.

Cu+X @ amorphous carbon hydrogenic films (X = 0, 5, 10 and 15 nm Ni layer): The photons cut-off energy, the optical linear equations and the electron phonon interactions

The using RF-magnetron sputtering, the Cu + X @ amorphous carbon hydrogenic films (X = 0, 5, 10 and 15 nm Ni layer) thin films that is; CuNiCH films, were deposited on glass substrates at room temperature. Considering that the sputtering process in the films accumulation stage is a completely random process, the configuration and number and diversity of the atoms and ions forming the films were also somewhat affected by this process. Therefor with consideration Nc = 4, Za = 2, Ne = 8, it can be seen that maximum value of coordination number β in these CuNiCH films to be was about 0.279. We found that CuCH films/or CuNiCH films with zero Ni layer, had maximum value of the penetration depths/or the skin depths in about of 380 nm. It can be seen that with increasing Ni layer thickness of films, the absorption edge in these films have a shifting behavior towards lower wavelength (blue-shift). The total range shifting of the absorption edge in these films was as a blue-shift from 2.05 to 2.015 eV. The CuNiCH films with 5 nm Ni have maximum value of optical density. Different linear fitting of ln (⍺) for films were obtained as y = Ax + B where 0.5<A<2 and 10<B < 12. The CuNiCH films with 5 nm Ni have minimum value of electron-phonon interaction at about of 34.3 eV. The empirical equation of CuNiCH films from this linear fitting was presented as Eg = 2.58–2.25Eu. Steepness parameters of CuNiCH films with 5 nm Ni have minimum value of 1.94 eV. Dispersion energy Ed for CuNiCH films with pure Cu content has maximum value of 17.87 eV.

Theoretical study of optoelectronic, elastic and mechanical properties of gallium modified barium titanate (Ba1-xGaxTiO3) perovskite ceramics by DFT

In this report, we study the gallium modified Barium titanate (Ga-BTO) Ba1-xGaxTiO3 with (x = 50 %) perovskite ceramics, which have not been synthesized experimentally to date. The density functional theory-based full potential linear augmented plane wave has been employed to determine the optoelectronic, elastic, and mechanical properties of pure and modified BaTiO3. Completely relaxed 2 × 2× 2 of primitive five atoms’ cells has been used for calculations. A large cut-off energy of 120 Ry has been used to eliminate the basics of plane wave-indicating wave functions. The influence of substitution of Ga on electronic structure and optical parameters such as reflectivity, refractivity, dielectric function, optical conductivity, extinction, and absorption coefficients are analyzed and elucidated with TDOS and PDOS. The Ga modified BTO manifests a forbidden energy gap of 1.84 eV. The static dielectric constant Ɛ1(o) has values of 8.8 and 100 for pure and modified compounds respectively. Ga dopant improved the polarizing power of BTO and for the doped BTO imaginary part, Ɛ2(ω)showed a prominent peak located at 3.9 eV. The optical properties show that perovskite compound substituted with Ga is a good absorber in the ultraviolet region and the modified material has a small value of reflectivity and static refractive index 12.2. The general profiles of optical spectra of modified BaTiO3 display highly desirable features like the prominent peaks of optical conductivity obtained at 4.2 and 5.8 eV for modified BTO that make it a promising candidate for optoelectronic and spintronics. Ga-modified BTO has higher ductility, modulus (169.96 GPa), and anisotropy (2.949) than pure BTO found by analyzing their elastic and mechanical properties.

The role of outflows in black-hole X-ray binaries

The hot inner flow in black-hole X-ray binaries is not just a static corona rotating around the black hole: it must be partially outflowing. It is therefore a mildly relativistic ``outflowing corona.'' We have developed a model in which Comptonization takes place in this outflowing corona. In all of our previous work, we assumed a rather high outflow speed of $0.8c$. Here, we investigate whether an outflow with a significantly lower speed can also reproduce the observations. Thus, in this work we consider an outflow speed of $0.1c$ or less. As in all of our previous work, we used a Monte Carlo code to compute not only the emergent X-ray spectra, but also the time lags that are introduced to the higher-energy photons with respect to the lower-energy ones via multiple scatterings. We also record the angle (with respect to the symmetry axis of the outflow) and the height at which photons escape. Our results are very similar to those of our previous work, with some small quantitative differences that can be easily explained. We are again able to quantitatively reproduce five observed correlations: (a) the time lag as a function of Fourier frequency, (b) the time lag as a function of photon energy, (c) the time lag as a function of Gamma , (d) the time lag as a function of the cutoff energy in the spectrum, and (e) the long-standing radio--X-ray correlation -- and all of them with only two parameters, which vary in the same ranges for all the correlations. Our model does not require a compact, narrow relativistic jet, although its presence does not affect the results. The essential ingredient of our model is the parabolic shape of the Comptonizing corona. The outflow speed plays a minor role. Furthermore, the bottom of the outflow, in the hard state, looks like a ``slab'' to the incoming soft photons from the disk, and this can explain the observed X-ray polarization, which is along the outflow. In the hard-intermediate state, we predict that the polarization of GX 339-4 will be perpendicular to the outflow.

First-principles calculation of structural, electronic, optical, and mechanical properties of SrVO3.

CONTEXT AND RESULTS: In this paper, the crystal structure, electronic, optical, and mechanical properties of SrVO3 have been systematically studied by first-principles calculation. The results show that the calculated lattice parameters are in good agreement with the experimental values of X-ray diffraction. The density of states is described in detail in this paper. By analyzing the crystal structure and electronic properties of SrVO3, the magnetic properties of SrVO3 are obtained from the one unpaired electrons of V and the exchange interaction between two V ions. At the same time, a detailed analysis of the optical properties of SrVO3 was conducted, and it was found that it is transparent in the visible light range. Finally, the mechanical properties of SrVO3 are calculated, which can provide some references for future research. COMPUTATIONAL METHOD: In this paper, a first-principles method based on density functional theory (DFT) is reported for PBE-GGA analysis using the plane wave-pseudo potential method in a quantum concentrate packet, U value of 7 eV to V-d and a U value of 2 eV to O-p, Grimme correction by DFT-D method. The k points in the Brillouin region are set to 4 × 4 × 4. The energy convergence criterion for self-consistent field calculation is set at 5.0 × 10-6 eV/atom, and the cutoff energy is 1170eV. In this paper, the force acting on each atom is not more than 0.01 eV/Å, the maximum stress is not more than 0.02GPa, and the maximum atomic displacement is 5 × 10-4Å.

Lattice Dynamics of Quasi-2D Perovskites from First Principles.

We present the vibrational properties and phonon dispersion for quasi-2D hybrid organic-inorganic perovskites (BA)2CsPb2I7, (HA)2CsPb2I7, (BA)2(MA)Pb2I7, and (HA)2(MA)Pb2I7 calculated from first principles. Given the highly complex nature of these compounds, we first perform careful benchmarking and convergence testing to identify suitable parameters to describe their structural features and vibrational properties. We find that the inclusion of van der Waals corrections on top of generalized gradient approximation (GGA) exchange-correlation functionals provides the best agreement for the equilibrium structure relative to experimental data. We also investigate the impact of the molecular orientation on the equilibrium structure of these layered perovskite systems. Our results suggest ground state ferroelectric alignment of molecular dipoles in the out-of-plane direction is unlikely and support the assignment of the centrosymmetric space group for the low-temperature phase of (HA)2(MA)Pb2I7. Finally, we compute vibrational properties under the harmonic approximation. We find that stringent energy cut-offs are required to obtain well-converged phonon properties, and once converged, the harmonic approximation can capture key physics for such a large, hybrid inorganic-organic system with vastly different atom types, masses, and interatomic interactions. We discuss the obtained phonon modes and dispersion behavior in the context of known properties for bulk 3D perovskites and ligand molecular crystals. While many vibrational properties are inherited from the parent systems, we also observe unique coupled vibrations that cannot be associated with vibrations of the pure constituent perovskite and ligand subphases. Energy dispersion of the low energy phonon branches primarily occurs in the in-plane direction and within the perovskite subphase and arises from bending and breathing modes of the equatorial Pb-I network within the perovskite octahedral plane. The analysis herein provides the foundation for future investigations on this class of materials, such as exciton-phonon coupling, phase transitions, and general temperature-dependent properties.