bluuebunny/crossref_metadata_2025 huggingface dataset:
Terahertz emission enhancement of GaAs-based photoconductive antennas via the nanodecoration of their surface by means of pulsed-laser-deposition of gold nanoparticles
Authors: Isgandarov E. , Pichon L. , Ropagnol X. , El Khakani M. A. , Ozaki T.
Published: April 2023

We report a systematic study of free-space terahertz (THz) emission from photoconductive antennas (PCAs) nanodecorated with gold nanoparticles (Au-NPs) deposited by using the pulsed laser deposition (PLD) technique. H-shaped dipole micro-structured PCAs fabricated on semi-insulating GaAs substrates were decorated under various PLD conditions. Thus, by increasing the number of laser ablation pulses (NLP) of the Au target, both the average size of Au-NPs and the surface loading of PCAs increase. Compared with non-decorated PCAs, those decorated with Au-NPs exhibit significant enhancement in the radiated THz pulse amplitude. A maximum enhancement of ∼2.3 was achieved at NLP = 1250. Under this optimal NLP condition, not only is the average Au-NP size (of ∼15 nm) favorable for light absorption via localized surface plasmons, but also the inter-distance between NPs, the light reflectance, and facilitated transport of photocarriers, all combine to yield a stronger THz field emission. For higher NLP (≥2000), NPs coalesce and tend to form continuous film NPs, which not only significantly limits the light scattering toward the GaAs underlying substrate, but also electrically shorts the PCA. Finally, the Au-NP decoration of GaAs PCAs was also found to improve their overall thermal conductivity, making them much more thermally stable than their non-decorated counterparts.
Network topology of interlocked chiral particles
Authors: Monderkamp Paul A. , Windisch Rika S. , Wittmann René , Löwen Hartmut
Published: April 2023

Self-assembly of chiral particles with an L-shape is explored by Monte-Carlo computer simulations in two spatial dimensions. For sufficiently high packing densities in confinement, a carpet-like texture emerges due to the interlocking of L-shaped particles, resembling a distorted smectic liquid crystalline layer pattern. From the positions of either of the two axes of the particles, two different types of layers can be extracted, which form distinct but complementary entangled networks. These coarse-grained network structures are then analyzed from a topological point of view. We propose a global charge conservation law by using an analogy to uniaxial smectics and show that the individual network topology can be steered by both confinement and particle geometry. Our topological analysis provides a general classification framework for applications to other intertwined dual networks.
An efficient decoherence scheme for fewest switches surface hopping method
Authors: Sindhu Aarti , Jain Amber
Published: April 2023

The fewest switches surface hopping method, in its original form, is known to be over-coherent. An accurate and efficient decoherence scheme is still a question of concern in the community. We propose a modification of the augmented fewest switches surface hopping (A-FSSH) scheme to make it efficient without compromising on its accuracy. We compare our proposed decoherence scheme with a recently proposed parameter-free decoherence scheme by Wang and co-workers. We show that for all model systems investigated here, our scheme is as accurate as the original A-FSSH method while at least 30 times more efficient. The decoherence scheme of Wang is more than ten times more efficient than our scheme although it does not give accurate results in the limit of large diabatic coupling.
Nitrogen-related point defects in homoepitaxial diamond (001) freestanding single crystals
Authors: Teraji Tokuyuki , Shinei Chikara
Published: April 2023

Controllability of nitrogen doping, types of nitrogen-related defects, and their charge states in homoepitaxial diamond (001) crystals were investigated. For these purposes, 15N-doped 12C-enriched free-standing chemical vapor deposited diamond (001) crystals were grown through long-time growth using 12C-enriched methane as the carbon source gas and 15N-enriched molecular nitrogen as the nitrogen source gas. The formation of non-epitaxial crystallites and growth hillocks was suppressed by the application of the oxygen-adding growth condition. Nitrogen was incorporated uniformly into the crystals, with a concentration variation of less than 10%. About 70% of the total nitrogen was substitutional nitrogen in a neutral charge state Ns0. Hydrogen was incorporated at approximately the same concentration as nitrogen. Both NV and NVH centers were predominantly negatively charged defect structures, i.e., NV− and NHV− centers. The concentrations of NHV− centers were less than 5% of the total nitrogen concentration. Nitrogen concentration in diamond crystals was controlled by changing the N/C gas ratio over a wide doping range from 10 ppb to 10 ppm. Nitrogen incorporation efficiency was found to be (1.5 ± 0.5) × 10−4 in this study.
An alternative approach to the osmotic second virial coefficient of protein solutions and its application to liquid–liquid phase separation
Authors: Surfaro Furio , Maier Ralph , Pastryk Kai-Florian , Zhang Fajun , Schreiber Frank , Roth Roland
Published: April 2023

The osmotic second virial coefficient B2 is an important parameter to describe the interactions and phase behavior of protein solutions, including colloidal systems and macromolecular solutions. Another key parameter to describe the driving force of the nucleation of a new phase is the supersaturation, which is used in the classical nucleation theory framework and is connected with the favorable contribution in the Gibbs free energy in the bulk solution. In this article, we establish a connection between B2 calculated from small angle x-ray scattering (SAXS) data and the values of B2 obtained from supersaturation measurements using thermodynamics considerations. The values of the second virial coefficient calculated employing this method agree with those determined via SAXS in the region near the liquid–liquid phase separation border for human serum albumin and bovine serum albumin. The general relations adopted are shown to be useful for the estimation of the second virial coefficient B2 for globular proteins, in the proximity of the binodal biphasic coexistent region.
Tunability of silicon clathrate film properties by controlled guest-occupation of their cages
Authors: Vollondat Romain , Stoeffler Daniel , Preziosi Daniele , Roques Stéphane , Slaoui Abdelilah , Fix Thomas
Published: April 2023

Type I and type II silicon clathrates are guest–host structures made of silicon polyhedral cages large enough to contain atoms that can be either inserted or evacuated with only a slight volume change of the structure. This feature is of interest not only for batteries or storage applications but also for tuning the properties of the silicon clathrate films. The thermal decomposition process can be tuned to obtain Na8Si46 and Na2<x<10Si136 silicon clathrate films on intrinsic and p-type c-Si (001) wafer. Here, from a unique synthesized NaxSi136 film, a range of resistivity of minimum four order of magnitude is possible by using post-synthesis treatments, switching from metallic to semiconductor behavior as the Na content is lowered. Extended exposition to sodium vapor allows us to obtain fully occupied Na24Si136 metallic films, and annealing under iodine vapor is a way to reach the guest-free Si136, a semiconducting metastable form of silicon with a 1.9 eV direct bandgap. Electrical measurements and resistance vs temperature measurements of the silicon clathrate films further discriminate the behavior of the various materials as the Na concentration is changing, additionally shouldered by density functional theory calculations for various guest occupations, further motivating the urge of an innovative pathway toward true guest-free type I and type II silicon clathrates.
Oscillatory Marangoni flow in a deep layer of a Carreau fluid
Authors: Baños R. , Arcos J. , Bautista O. , Méndez F. , Martínez-Suástegui L.
Published: April 2023

We study the spreading dynamics of an insoluble and non-diffusive surfactant on the free surface of a deep layer of a Carreau fluid. When a non-uniform distribution of surfactant is imposed on the free surface of an initially motionless fluid, variations in surface tension are induced, causing the fluid motion from regions of lower surface tension to those of higher tension. Such movement redistributes the surfactant concentration until a uniform condition is reached. The two-dimensional momentum and convection–diffusion equations are employed to determine the hydrodynamics in the deep fluid layer and the evolution of the surfactant on the fluid surface. The modified vorticity-stream function formulation is used to solve numerically the hydrodynamic field, where the non-Newtonian dependent variables of the problem are decomposed into a Newtonian part and a non-Newtonian contribution. One of the most critical variables in practical applications regarding this phenomenon concerns the time required for the surfactant to reach a uniform distribution over the interface. The results show that the dimensionless parameters that control the decay of the variations in surfactant concentration in time are the Reynolds number Re, the fluid behavior index n, and ε, reflecting the influence of the inertia of the fluid. The results show that the temporal decay of the surfactant concentration on the fluid surface increases significantly for high values of the Reynolds number, it is more attenuated in pseudoplastic fluids than in Newtonian fluids, and the surfactant concentration decay exhibits asymmetric oscillations when inertial effects increase.
Balance between thermal stability and operation speed realized by Ti gradient doping in Sb2Te3 phase-change memory
Authors: Zeng Yuntao , Liu Xiangjun , Xu Ming , Cheng Xiaomin , Miao Xiangshui
Published: April 2023

Phase-change memory (PCM) is one of the leading candidates for the next generation nonvolatile memory. As a growth-dominated crystalline material, Sb2Te3 is of rapid crystallization speed while its poor thermal stability limits its application. Doping Ti can significantly enhance its amorphous stability but inevitably slows down its crystallization speed. How to balance the contradiction between thermal stability and operation speed remains challenging. In this work, we proposed a gradient Ti-doped Sb2Te3 phase-change material and device. This gradient doping strategy compensates for the negative effect of Ti doping on the crystallization rate of Sb2Te3 via the template effect of the lower doping concentration layer. Very small lattice mismatch between the Sb2Te3 layers with different Ti doping concentrations is verified by x-ray diffraction characterization. The crystallization temperature of a gradient Ti-doped Sb2Te3 thin film is raised up to 172.6 °C and the same 50 ns operation speed as a pure Sb2Te3 device is achieved in the corresponding PCM device. Furthermore, the gradient distribution of Ti elements and the corresponding progressive crystallization phenomenon are verified by transmission electron microscopy revealing the microscopic origin of rapid crystallization speed. Therefore, with our gradient doping strategy, the amorphous stability is improved without sacrificing the crystallization speed in PCM.
Sparse tensor based nuclear gradients for periodic Hartree–Fock and low-scaling correlated wave function methods in the CP2K software package: A massively parallel and GPU accelerated implementation
Authors: Bussy Augustin , Schütt Ole , Hutter Jürg
Published: April 2023

The development of novel double-hybrid density functionals offers new levels of accuracy and is leading to fresh insights into the fundamental properties of matter. Hartree–Fock exact exchange and correlated wave function methods, such as second-order Møller–Plesset (MP2) and direct random phase approximation (dRPA), are usually required to build such functionals. Their high computational cost is a concern, and their application to large and periodic systems is, therefore, limited. In this work, low-scaling methods for Hartree–Fock exchange (HFX), SOS-MP2, and direct RPA energy gradients are developed and implemented in the CP2K software package. The use of the resolution-of-the-identity approximation with a short range metric and atom-centered basis functions leads to sparsity, allowing for sparse tensor contractions to take place. These operations are efficiently performed with the newly developed Distributed Block-sparse Tensors (DBT) and Distributed Block-sparse Matrices (DBM) libraries, which scale to hundreds of graphics processing unit (GPU) nodes. The resulting methods, resolution-of-the-identity (RI)-HFX, SOS-MP2, and dRPA, were benchmarked on large supercomputers. They exhibit favorable sub-cubic scaling with system size, good strong scaling performance, and GPU acceleration up to a factor of 3. These developments will allow for double-hybrid level calculations of large and periodic condensed phase systems to take place on a more regular basis.
Time and temperature dependent magnetic viscosity experiments on Sr/Co nanoferrite particles
Authors: Maltoni Pierfrancesco , Varvaro Gaspare , Abdolrahimi Maryam , Peddis Davide , Mathieu Roland
Published: April 2023

Magnetic viscosity experiments have been performed in order to investigate the magnetization reversal in Sr nanoferrite particles (nanoscale SrFe12O19) and interacting Sr/Co nanoferrite particles (SrFe12O19–CoFe2O4 nanocomposites). The magnetic viscosity S = d M ( t ) / d l n ( t ), where M ( t ) is the magnetization as a function of time, has been collected. For Sr nanoferrite S shows a maximum close to the coercive field, reflecting the relation between S and the energy barrier distribution. We evidence that magnetic viscosity experiments on Sr nanoferrite and interacting Sr/Co nanoferrite particles provide reliable qualitative results for the different magnetic field sweep rate and saturating field H s a t considered. In addition, the activation volumes extracted from the magnetic viscosity experiments performed at different temperatures on Sr nanoferrite are quantitatively correlated to anisotropy changes.
Including vibrational effects in magnetic circular dichroism spectrum calculations in the framework of excited state dynamics
Authors: Foglia Nicolás , De Souza Bernardo , Maganas Dimitrios , Neese Frank
Published: April 2023

In this work, we present a computational approach that is able to incorporate vibrational effects in the computations of magnetic circular dichroism (MCD) spectra. The method combines our previous implementations to model absorption as well as fluorescence and phosphorescence spectra in the framework of excited state dynamics with a new technique to calculate MCD intensities, where molecular orientational averages are treated via semi-numerical quadrature. The implementation relies on a path integral approach that is employed to compute nuclear dynamics under the harmonic oscillator approximation (accounting for the nuclear potential energy surface) together with quasi-degenerate perturbative theory (to include the perturbation of an external magnetic field). We evaluate our implementation with a selected molecular set consisting of five aromatic organic molecules, namely, 1,4-benzoquinone, naphthalene, 2-naphthylamine, 2-naphthaldehyde, and benzene; we also included the MnO4− and the [Co(NH3)6]3+ transition metal complexes. This set is used to validate the ability of the approach to compute MCD A- and B-terms in conjunction with time-dependent density functional theory. The computed intensities are discussed in terms of the overall quality of the electronic structure treatments, vibrational modes, and the quality of the nuclear Hessians. It is shown that in the cases in which the potential energy surface is accurately represented, electric dipole-forbidden transitions are vibrationally activated, producing intensities relative to the dipole-allowed transitions in the same order of magnitude as the experimental measurements.
Influence of the load conditions on the acoustic signature of a tip-loaded propeller with winglets
Authors: Posa A. , Broglia R.
Published: April 2023

The Ffowcs-Williams and Hawkings acoustic analogy was exploited to reconstruct the acoustic signature of a tip-loaded propeller with winglets across a range of working conditions, from design toward higher loads. Results of Large-Eddy Simulations, conducted on a computational grid consisting of about 5 × 109 points, were utilized. For decreasing values of the advance coefficient, that is for increasing rotational speeds of the propeller, the rise of the values of acoustic pressure was found faster than linear, approximating a logarithmic growth. This result was verified in line with the behavior by the turbulent fluctuations on the surface of the propeller and in its wake system, which were the major sources of the loading and quadrupole components of sound, respectively. The former was the leading one on the propeller plane and at radial coordinates away from the wake system, while the latter was higher at smaller radial coordinates in the vicinity of the wake system. In addition, increasing loads on the propeller blades resulted in an outward shift of the boundary of the computational domain where the lead of the acoustic signature switched from the non-linear sources within the wake to the linear ones on the propeller surface.
First-principles study for the electric field influence on electronic and optical properties of AlN/g-C3N4 heterostructure
Authors: Liu Chenxi , Dai Zhonghua , Hou Jie , Zhang Lili , Gu Shuitao
Published: April 2023

Constructing a heterostructure and applying an external electric field are effective methods for enhancing photocatalytic efficiency. In this study, we systematically investigate the electronic and optical properties of an AlN/g-C3N4 heterostructure under varying electric fields using first principles. Our findings indicate that the AlN/g-C3N4 heterostructure demonstrates high stability, and van der Waals (vdW) interactions exist between the interfaces. Compared with monolayers AlN and g-C3N4, the reduced bandgap of AlN/g-C3N4 enhances electron escape ability. Furthermore, we observe that the bandgap of AlN/g-C3N4 reduces when an electric field is applied and the band alignment changes. Importantly, −0.4 V/Å AlN/g-C3N4 is not only a type-II heterostructure, forming a built-in electric field, but it also has a band alignment that spans the redox reaction of water. Consequently, the compound rate of electron–hole pairs substantially reduces, enhancing the possibility of AlN/g-C3N4 photocatalytic water splitting. Our findings provide a theoretical foundation for related experimental preparations.
Communication: Non-adiabatic derivative coupling elements for the coupled cluster singles and doubles model
Authors: Kjønstad Eirik F. , Koch Henrik
Published: April 2023

We present an efficient implementation of analytical non-adiabatic derivative coupling elements for the coupled cluster singles and doubles model. The derivative coupling elements are evaluated in a biorthonormal formulation in which the nuclear derivative acts on the right electronic state, where this state is biorthonormal with respect to the set of left states. This stands in contrast to earlier implementations based on normalized states and a gradient formula for the derivative coupling. As an illustration of the implementation, we determine a minimum energy conical intersection between the nπ* and ππ* states in the nucleobase thymine.
Experimental observation of diffractive retroreflection from a dielectric metasurface
Authors: Kupriianov Anton S. , Khardikov Vyacheslav V. , Domina Kateryna , Prosvirnin Sergey L. , Han Wei , Tuz Vladimir R.
Published: April 2023

The non-specular reflection scenario is considered important for many practical applications of gratings because this regime corresponds to the maximum efficiency of diffraction. Retroreflection is a particular case of a non-specular scenario when a grating returns a large portion of the incident light back to its source. We propose a detailed quasi-optic (microwave) experimental study of the retroreflection phenomenon in dielectric metasurfaces. Our study is supplemented by an analytical description and full-wave numerical simulation. The experimental sample of the metasurface is constructed as an array of disk-shaped low-loss ceramic resonators inserted in a host with air-like material properties. To ensure efficient reflection, the metasurface is coated on one side with a metallic foil. The conditions of retroreflection for any direction and polarization of an incident wave are demonstrated in both far-field and near-field experiments. The main contribution to the non-specular reflection of the Mie-type (HE 11) mode of the disk-shaped resonators forming the metasurface is revealed. The high efficiency of retroreflection in both TE (transverse electric) and TM (transverse magnetic) polarizations allows us to consider our metasurface as a prototype of planar grating rulers for high-precision displacement measurements.
On the allosteric puzzle and pocket crosstalk through computational means
Authors: Aguti Riccardo , Bernetti Mattia , Bosio Stefano , Decherchi Sergio , Cavalli Andrea
Published: April 2023

Allostery is a constitutive, albeit often elusive, feature of biomolecular systems, which heavily determines their functioning. Its mechanical, entropic, long-range, ligand, and environment-dependent nature creates far from trivial interplays between residues and, in general, the secondary structure of proteins. This intricate scenario is mirrored in computational terms as different notions of “correlation” among residues and pockets can lead to different conclusions and outcomes. In this article, we put on a common ground and challenge three computational approaches for the correlation estimation task and apply them to three diverse targets of pharmaceutical interest: the androgen A2A receptor, the androgen receptor, and the EGFR kinase domain. Results show that partial results consensus can be attained, yet different notions lead to pointing the attention to different pockets and communications.
Fabrication of an atomically smooth Ge(111) surface by Au-induced crystallization at 170 °C
Authors: Sunthornpan Narin , Hirose Ken , Kyuno Kentaro
Published: April 2023

Crystalline Ge layer fabricated via layer-exchange metal-induced crystallization is a promising candidate as a seed layer for the epitaxial growth of III–V semiconductor thin films for multijunction solar cells. However, small crystalline islands that grow on top of the crystalline Ge layer are a problem, which roughens the surface and hinders subsequent epitaxial growth. Considering the effect of heating rate on the Au-induced crystallization behavior of Ge, it is found that the temperature required for the island growth in the top Ge layer was higher than that for the bottom layer. By carefully choosing the annealing conditions, the growth of the top Ge layer can be avoided resulting in an atomically smooth Ge(111) surface.
The effects of the shape of a capsid on the ejection rate of a single polymer chain through a nanopore
Authors: Park Chung Bin , Sung Bong June
Published: April 2023

The shape of a viral capsid affects the equilibrium conformation of DNA inside the capsid: the equilibrium DNA conformation inside a spherical capsid is a concentric spool while the equilibrium conformation inside an elongated capsid is a twisted toroid. The conformation of DNA, jammed inside the capsid due to high internal pressure, influences the ejection kinetics of the DNA from the capsid. Therefore, one would expect that the DNA ejection kinetics would be subject to the shape of the viral capsid. The effects of the capsid shape on the ejection, however, remain elusive partly due to a plethora of viral capsid shapes. In this work, we perform Langevin dynamics simulations for the ejection of a polymer chain from three different types of viral capsids: (1) spherical, (2) cubic, and (3) cuboid capsids. We find that the ejection rate of the polymer chain from the spherical capsid is much faster than that from either cubic or cuboid capsids. The polymer chain in the spherical capsid may undergo collective rotational relaxation more readily such that the polymer chain becomes more mobile inside the spherical capsid, which enhances the ejection kinetics. On the other hand, a threading motion is dominant inside cubic and cuboid capsids. We also find that the effects of the collective rotational motion become more significant for a more rigid chain inside a capsid.
Robust temperature–strain coupling in phase and shape evolution of MoTe2 nanosheets
Authors: Lu Donglin , Luo Chaobo , Qi Xiang , Zhong Jianxin
Published: April 2023

Molybdenum ditelluride (MoTe2) has a stable semiconducting hexagonal (2H) phase and a metastable metallic distorted octahedral (1T′) phase at the same time, which attracts much attention due to its attractive properties. However, the mechanism of phase and shape evolution in the preparation of MoTe2 is still unclear, which limits the controllable preparation and the wider device application of MoTe2. Here, we prepare few-layer MoTe2 with controllable phase and shape by using MoO3 and Te powders as precursors. With this method, triangle and hexagon 2H MoTe2 can be prepared, and long-strip and irregular 1T′ MoTe2 can be obtained. The phase and shape of as-prepared MoTe2 are determined by the coupling effect in the growth temperature and the lattice strain between 2H and 1T′ MoTe2. Low growth temperature combined with low Te concentration could induce small growth strain potential, leading to the growth of triangle and hexagon 2H MoTe2. While high growth temperature combined with high Te concentration could induce large strain potential, which is conducive to the preparation of long-strip and irregular 1T′ MoTe2. This study deeply investigates the evolution mechanism of phase and shape in MoTe2 growth, which has important guiding significance for the controllable preparation of phase and shape of other two-dimensional materials.
Unified description for the temperature dependence of mobility in liquids
Authors: Yungbluth J. C. , Medvedev G. A. , Savoie B. M. , Caruthers J. M.
Published: April 2023

The physical mechanisms governing molecular mobility in liquids remain unresolved. Whether distinct mechanisms govern mobility in the Arrhenian and super-cooled regions, and whether the mobility in these regions can be unified remain open questions. Here, molecular dynamics simulations were used to search for a structural property with a temperature dependence related by a simple functional form to the temperature dependent translational diffusion coefficient, Dtrans. The logarithm of Dtrans was found to be a two-parameter function of F2, where F2 is the mean squared-force per molecule. The relationship is demonstrated for all systems investigated: a three-bead model of ortho-terphenyl, an 80:20 binary mixture of Lennard-Jones spheres, and a system of Lennard-Jones dumbbells. For each system, the relationship holds for the entire range of temperatures under both constant pressure and constant density conditions. The same F2-based expression describes the translational diffusion coefficient in the Arrhenian, crossover, and super-Arrhenian regions.
Spatial modulation of refractive index in a dense atomic ensemble using Laguerre–Gaussian beams
Authors: Peng Chen , Zheng Kang , Jin Rui-Bo , Ding Chunling , Hao Xiangying
Published: April 2023

We propose a scheme to investigate the spatial modulation of the refractive index in a dense atomic ensemble under the action of the Laguerre–Gaussian (LG) beams. Theoretical derivations based on a density-matrix approach associated with numerical simulations are utilized to study the behaviors of the index of refraction, showing that the azimuthal and radial mode indices (i.e., l 2 and p 2) of the LG beams significantly affect the real and imaginary parts of the refractive index. To be specific, the number of the dispersive peaks is determined by ( p 2 + 1 ) | l 2 |, and there are 2 | l 2 | lossless petals in conjunction with p 2 concentric absorption rings centered on the vortex center. Furthermore, by tuning the phase values of the electric and magnetic components of the electromagnetic field, the index of refraction can be drastically tuned from negative to zero to positive and accompanied by periodic absorption and amplification. This investigation provides a powerful tool for manipulating the index of refraction through a nonlinear interaction between atoms and the vortex beams and suggests potential applications in optical switching, logic gates, and optical storage with spatially varying refractive indices.
Crystal structure determination of a new monoclinic phase in NiMn system in a self-assembled chessboard-like microstructure
Authors: Lal Das Aman Kumar , Rout Gaurav Dilip , Pal Avnish Singh , Basu Joysurya
Published: April 2023

Vacuum induction melted equi-atomic NiMn alloy has been studied through x-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern of the as-solidified alloy may be matched with the tI2 η′-NiMn phase and the cF4 Ni3Mn phase simultaneously. In the TEM bright field image of the same alloy, alternating bright and dark contrast with chessboard-like appearance is observed. Electron diffraction patterns from the bright phase match with the tI2 NiMn phase. The electron diffraction patterns from the dark phase are related to the tetragonal phase with additional superlattice reflection along [110] and [112]. The crystal structure of the new phase has been found to be polymorphically related mP8 phase with space group P 2/m (a = 5.02 Å, b = 5.16 Å, c = 3.61 Å). The phase has not been reported so far in the Ni–Mn system. The chessboard-like morphology between a tetragonal and monoclinic phase is being reported for the first time.
Machine learning for shock compression of solids using scarce data
Authors: Balakrishnan Sangeeth , VanGessel Francis G. , Barnes Brian C. , Doherty Ruth M. , Wilson William H. , Boukouvalas Zois , Fuge Mark D. , Chung Peter W.
Published: April 2023

Data-driven machine learning techniques can be useful for the rapid evaluation of material properties in extreme environments, particularly in cases where direct access to the materials is not possible. Such problems occur in high-throughput material screening and material design approaches where many candidates may not be amenable to direct experimental examination. In this paper, we perform an exhaustive examination of the applicability of machine learning for the estimation of isothermal shock compression properties, specifically the shock Hugoniot, for diverse material systems. A comprehensive analysis is conducted where effects of scarce data, variances in source data, feature choices, and model choices are systematically explored. New modeling strategies are introduced based on feature engineering, including a feature augmentation approach, to mitigate the effects of scarce data. The findings show significant promise of machine learning techniques for design and discovery of materials suited for shock compression applications.
Interface traps, correlated mobility fluctuations, and low-frequency noise in metal–oxide–semiconductor transistors
Authors: Fleetwood D. M.
Published: April 2023

Interface traps generally are not considered to be likely sources of low-frequency (LF) noise and/or random telegraph noise (RTN) in metal–oxide–semiconductor (MOS) devices because the longer carrier exchange times of border traps are more consistent with experimental observations. In contrast, correlated mobility fluctuations due to remote Coulomb scattering from charged border traps cannot explain the unexpectedly large LF noise and/or RTN observed in some MOS devices. In this Letter it is proposed that equilibrium fluctuations in interface-trap concentrations caused by hydrogen-induced activation and passivation reactions can lead to enhanced LF noise and RTN. This mechanism adds to other noise sources, including border traps, random dopants, and bulk-Si defect clusters.
Vacuum ultraviolet photodissociation dynamics of OCS via the F Rydberg state: The O (3PJ=2,1,0) product channels
Authors: Luo Chang , Zhou Lin , Chen Wentao , Yuan Daofu , Yu Shengrui , Wang Siwen , Parker David H. , Yang Xueming , Wang Xingan
Published: April 2023

We study the vacuum ultraviolet (VUV) photodissociation dynamics of carbonyl sulfide (OCS) by using the time sliced velocity map ion imaging technique. Experimental images of the dissociative O (3PJ=0,1,2) products were acquired at five VUV photolysis wavelengths from 133.26 to 139.96 nm that correspond to the F Rydberg state of OCS. High vibrational states of the carbon monosulfide (CS) co-products are partially resolved in the images. The product total kinetic energy releases, angular distributions, and the product state branching ratios were derived from the experimental images. Notably, it is found that the anisotropic parameters change systematically with the photolysis wavelength. The anisotropic parameters and the product state branching ratios are significantly sensitive to the J quantum number of the O (3PJ) products. The phenomenon indicates that multiple nonadiabatic pathways are strongly involved in the photodissociation processes.
ænet-PyTorch: A GPU-supported implementation for machine learning atomic potentials training
Authors: López-Zorrilla Jon , Aretxabaleta Xabier M. , Yeu In Won , Etxebarria Iñigo , Manzano Hegoi , Artrith Nongnuch
Published: April 2023

In this work, we present ænet-PyTorch, a PyTorch-based implementation for training artificial neural network-based machine learning interatomic potentials. Developed as an extension of the atomic energy network (ænet), ænet-PyTorch provides access to all the tools included in ænet for the application and usage of the potentials. The package has been designed as an alternative to the internal training capabilities of ænet, leveraging the power of graphic processing units to facilitate direct training on forces in addition to energies. This leads to a substantial reduction of the training time by one to two orders of magnitude compared to the central processing unit implementation, enabling direct training on forces for systems beyond small molecules. Here, we demonstrate the main features of ænet-PyTorch and show its performance on open databases. Our results show that training on all the force information within a dataset is not necessary, and including between 10% and 20% of the force information is sufficient to achieve optimally accurate interatomic potentials with the least computational resources.
The effect of energy level degeneracy on symmetry-breaking charge transfer: Excited octupolar dyes
Authors: Siplivy Nikolay B. , Ivanov Anatoly I.
Published: April 2023

A three-level model of symmetry-breaking charge transfer (SBCT) in excited octupolar molecules is developed. The model describes the joint dynamics of the solvent and the dye in the excited state. For this, a distribution function in the space of two reaction coordinates is introduced. An evolution equation of this function is derived. A strict definition of the reaction coordinates is given, and its dynamic characteristics are determined. The free energy surface in the space of these coordinates is calculated. To quantify the symmetry-breaking degree, a two-dimensional dissymmetry vector is introduced. The model predicts the absence of SBCT in apolar solvents and an abrupt increase in its degree to half the maximum value in weakly polar solvents. The dye dipole moment is revealed to be directed along a molecular arm independently of the direction and the strength of the electric field of the solvent created by its orientational polarization. The conditions for the occurrence and nature of this effect are discussed. The effect of the degeneracy of excited states, which is inherent in octupolar dyes in the excited state, on SBCT is revealed. Degeneracy of energy levels is shown to lead to a significant increase in the symmetry-breaking degree. The effect of SBCT on the dependence of the Stokes on the solvent polarity is calculated and compared with the available experimental data.
Eutectic crystallization and melting in sharp concentration gradients
Authors: Gusak Andriy , Titova Anastasiia
Published: April 2023

The initial stages of contact melting and eutectic crystallization in sharp concentration gradients between two crystalline components are studied and simulated analytically and numerically. Contact melting is shown to become possible only after the formation of some critical width of solid solutions. Crystallization in the sharp concentration gradient may lead to the formation of periodic structures in the interface vicinity. In addition, at least for the eutectic systems of Ag–Cu type, the threshold temperature should exist, under which the “precipitation + growth” mechanism of crystallization may be changed to “polymorphic crystallization with eutectic composition + subsequent spinodal decomposition.”
Experimental synthesis of higher-order Poincaré sphere beam array with spatial coherence engineering
Authors: Liu Yonglei , Dong Zhen , Wang Fei , Cai Yangjian , Chen Yahong
Published: April 2023

We propose a compact method to experimentally synthesize a class of vector beam arrays with periodic higher-order Poincaré sphere (HOPS) polarization states by engineering the spatial coherence structure of a partially coherent light source. We demonstrate that the spatial coherence structure and polarization state of the partially coherent source can be simultaneously controlled using a phase-only spatial light modulator and a common-path interferometric arrangement with the aid of a complex-random-mode representation method. We show experimentally that the polarization state of a single HOPS beam in the source plane can be mapped into a beam array generated in the far field, and the degree of polarization of the beam array can be conveniently controlled with spatial coherence engineering. Our method provides an alternative way to synthesize beam arrays with structured coherence and polarization properties.
Small scale magnetic field source detection using recessed atomic vapor cell
Authors: Hu Min , Jiang Weiming , Ye Hangfei , Dong Haifeng , Liu Yuanxing
Published: April 2023

With the development of high spatial resolution spin image and magnetic field distribution measurement in atomic vapor cell, one can localize the position and calculate the magnetic moment of the field source around the cell. However, traditional cubic or spherical vapor cell can only measure the magnetic field distribution on one side of the field source, which limits the precision of the field inversion results. Here, we use a recessed atomic vapor cell to obtain field distribution around the source, which is positioned at the center of the cell. The magnetic field distributions around five sides of the field source are measured using movable stages and digital micro-mirror device. We combine the Levenberg–Marquardt algorithm with a genetic algorithm as the magnetic source localization algorithm to realize a quick global search as well as a precise local extreme point search. We obtain a spatial resolution of 219.2 × 387.0 × 451.5 μ m 3 and a magnetic field sensitivity of 0.06  nT / Hz 1 / 2 in a volume pixel of 0.0383  mm 3. The error in the localization of the magnetic source is 1.295 mm in the x direction, 185  μ m in the y direction, and 40  μ m in the z direction. The field distribution measurement method using recessed atomic vapor cell and related inversion algorithm demonstrated here have great potential applications in small scale field source detection of biology and materials science.
The effect of 1H offset and flip-angle on heteronuclear decoupling efficiency in ROSPAC pulsed sequence: A Floquet description
Authors: Simion Andrea , Ernst Matthias , Filip Claudiu
Published: April 2023

A new heteronuclear decoupling sequence for solid-state NMR and magic angle spinning faster than 60 kHz was recently introduced [Simion et al., J. Chem. Phys. 157, 014202 (2022)]. It was dubbed ROtor-Synchronized Phase-Alternated Cycles (ROSPAC), and it offers robustness for a large range of chemical shifts and low radio-frequency (RF) powers and is almost independent of the radio-frequency power. Here, we theoretically explore the robustness of the ROSPAC sequence toward 1H offset and RF field inhomogeneities, as well as the spacing effect of the π pulses on the decoupling efficiency. We use a generalized theoretical framework based on the Floquet theory to assess these parameters. The optimum decoupling conditions, where the magnitude of the second-order cross-terms and first-order resonance conditions are small, were identified.
A semilocal machine-learning correction to density functional approximations
Authors: Wang JingChun , Wang Yao , Xu Rui-Xue , Chen GuanHua , Zheng Xiao
Published: April 2023

Machine learning (ML) has demonstrated its potential usefulness for the development of density functional theory methods. In this work, we construct an ML model to correct the density functional approximations, which adopts semilocal descriptors of electron density and density derivative and is trained by accurate reference data of relative and absolute energies. The resulting ML-corrected functional is tested on a comprehensive dataset including various types of energetic properties. Particularly, the ML-corrected Becke’s three parameters and the Lee–Yang–Parr correlation (B3LYP) functional achieves a substantial improvement over the original B3LYP on the prediction of total energies of atoms and molecules and atomization energies, and a marginal improvement on the prediction of ionization potentials, electron affinities, and bond dissociation energies; whereas, it preserves the same level of accuracy for isomerization energies and reaction barrier heights. The ML-corrected functional allows for fully self-consistent-field calculation with similar efficiency to the parent functional. This study highlights the progress of building an ML correction toward achieving a functional that performs uniformly better than B3LYP.
Leveraging uncertainty estimates and derivative information in Gaussian process regression for efficient collection and use of molecular simulation data
Authors: Monroe Jacob I. , Krekelberg William P. , McDannald Austin , Shen Vincent K.
Published: April 2023

We introduce Gaussian Process Regression (GPR) as an enhanced method of thermodynamic extrapolation and interpolation. The heteroscedastic GPR models that we introduce automatically weight provided information by its estimated uncertainty, allowing for the incorporation of highly uncertain, high-order derivative information. By the linearity of the derivative operator, GPR models naturally handle derivative information and, with appropriate likelihood models that incorporate heterogeneous uncertainties, are able to identify estimates of functions for which the provided observations and derivatives are inconsistent due to the sampling bias that is common in molecular simulations. Since we utilize kernels that form complete bases on the function space to be learned, the estimated uncertainty in the model takes into account that of the functional form itself, in contrast to polynomial interpolation, which explicitly assumes the functional form to be fixed. We apply GPR models to a variety of data sources and assess various active learning strategies, identifying when specific options will be most useful. Our active-learning data collection based on GPR models incorporating derivative information is finally applied to tracing vapor–liquid equilibrium for a single-component Lennard-Jones fluid, which we show represents a powerful generalization to previous extrapolation strategies and Gibbs–Duhem integration. A suite of tools implementing these methods is provided at https://github.com/usnistgov/thermo-extrap.
From fiber Bragg gratings to coaxial cable Bragg gratings: One-dimensional microwave quasi-periodic photonic crystals
Authors: Zhu Chen , Alsalman Osamah , Huang Jie
Published: April 2023

Coaxial cables and optical fibers are two types of cylindrical waveguides used in telecommunications. Fiber Bragg gratings (FBGs) have found successful applications in various fields, such as optical communications, fiber lasers, and fiber-optic sensing. In this paper, we propose and numerically investigate the implementations of various fiber Bragg configurations, including uniform, chirped, apodized, and phase-shifted configurations, on coaxial cables to generate the corresponding special types of coaxial cable Bragg gratings (CCBGs). The simulation results of different CCBGs match well with the well-known FBG theories. It is demonstrated that the reflection spectrum of a CCBG can be flexibly tailored by introducing various quasi-periodic perturbations in the permittivity of the dielectric layer along the coaxial cable. The proposed special types of CCBGs with unique characteristics could find potential applications in radio frequency signal processing, communication, and sensing fields.
Removing the performance bottleneck of pressure–temperature flash calculations during both the online and offline stages by using physics-informed neural networks
Authors: Wu Yuanqing , Sun Shuyu
Published: April 2023

Pressure–temperature (PT) flash calculations are a performance bottleneck of compositional-flow simulations. With the sparse grid surrogate, the computing burden of PT flash calculations is shifted from the online stage to the offline stage of the compositional-flow simulations, and a great acceleration is achieved. It is known that the data-driven neural network can also be a surrogate of PT flash calculations. However, flash calculations are carried out in the training stage, i.e., the offline stage, which means the computing burden of PT flash calculations still exists in the offline stage. With physics-informed neural networks, the two heavy-burden routines of PT flash calculations, the successive substitution technique and stability analysis, are not carried out in the offline stage, and therefore, the computing burden in the offline stage is removed. After training, the phase condition and the compositions are the output of the neural network. The numerical experiments demonstrate the correctness and the applicability of the work. To the best of our knowledge, this is the first work to remove the performance bottleneck of PT flash calculations during both the online and offline stages of compositional-flow simulations.
Solid-state Li-ion batteries with carbon microfiber electrodes via 3D electrospinning
Authors: Arrese-Igor Mikel , Vong Michel , Orue Ander , Kassanos Panagiotis , George Chandramohan , Aguesse Frédéric , Mysyk Roman , Radacsi Norbert , López-Aranguren Pedro
Published: April 2023

Self-standing carbon fiber electrodes hold promise for solid-state battery technology owing to their networked structures improving interparticle connectivity, robustness contributing to mechanical integrity, and surface sites confining Li dendrites. We here evaluate carbonized 3D electrospun fibers filled with polymer electrolytes as anodes in solid-state lithium half cells. Microscopic analysis of the cells demonstrates the high wettability of carbon fibers with electrolytes, promoting an intimate contact between electrolytes and fibers. Solid-state cells delivered high initial capacities up to ∼300 mAh g−1, although the latter cycles were characterized by gradual capacity fade (∼100 mAh g−1 in the 100th cycle with nearly 100% coulombic efficiency), attributed to the onset of parasitic reactions increasing the cell resistance and polarization. When these were benchmarked against similar cells but with the liquid electrolyte, it was found that Li storage in these fiber electrodes is intermediate between graphite and hard carbon in terms of lithiation voltage (vs Li/Li+), corroborating with the nature of carbon assessed by XRD and Raman analysis. These observations can contribute to further development and optimization of solid-state batteries with 3D electrospun carbon fiber electrodes.