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Microscopic picture of paraelectric perovskites from structural prototypes

Physical Review Research 2022年第1期4卷 L012042-L012042页

作者： Michele Kotiuga Samed Halilov Boris Kozinsky Marco Fornari Nicola Marzari Giovanni Pizzi Theory and Simulation of Materials (THEOS) National Centre for Computational Design and Discovery of Novel Materials (MARVEL) École Polytechnique Fédérale de Lausanne CH-1015 Lausanne Switzerland Designed Material Technologies LLC P.O. Box 14548 Richmond Virginia 23221-9998 USA John A. Paulson School of Engineering and Applied Sciences Harvard University 29 Oxford Street Cambridge Massachusetts 02138 USA Robert Bosch LLC Research and Technology Center Cambridge Massachusetts 02139 USA Department of Physics and Science of Advanced Materials Program Central Michigan University Mt. Pleasant Michigan 48859 USA

We highlight with first-principles molecular dynamics the persistence of intrinsic 〈111〉 Ti off-centerings for BaTiO3 in its cubic paraelectric phase. Intriguingly, these are inconsistent with the Pm3¯m space group often used to atomistically model this phase using density-functional theory or similar methods. Therefore, we deploy a systematic symmetry analysis to construct representative structural models in the form of supercells that satisfy a desired point symmetry but are built from the combination of lower-symmetry primitive cells. We define as structural prototypes the smallest of these that are both energetically and dynamically stable. Remarkably, two 40-atom prototypes can be identified for paraelectric BaTiO3; these are also common to many other ABO3 perovskites. These prototypes can offer structural models of paraelectric phases that can be used for the computational engineering of functional materials. Last, we show that the emergence of B-cation off-centerings and the primitive-cell phonon instabilities is controlled by the equilibrium volume, in turn, dictated by the filler A cation.

关键词： Crystal symmetry Ferroelectricity Structural order parameter Paraelectrics

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Elemental analysis of tsunami soil collected from Aceh of Indonesia using scanning electron microscope-energy dispersive x-ray (SEM-EDX)

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AIP Conference Proceedings 2023年第1期2480卷

作者： Muliadi Ramli Rara Mitaphonna Kurnia Lahna Nasrullah Idris Department of Chemistry Faculty of Mathematics and Natural Sciences Universitas Syiah Kuala Jl. Syech Abdurrauf No. 3 Darussalam 23111 Banda Aceh Aceh Indonesia Doctoral Program of Mathematics and Applied Sciences Universitas Syiah Kuala 23111 Banda Aceh Indonesia Department of Physics Faculty of Mathematics and Natural Sciences Universitas Syiah Kuala Jl. Syech Abdurrauf No. 3 Darussalam 23111 Banda Aceh Aceh Indonesia

Characterization of soil impacted by 2004 Indian Ocean tsunami giant disaster was carried out using a Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX) for investigating its chemical composition. The soil sample was collected from several part of Aceh province of Indonesia. Aceh region is well known as a worst flood land by the 2004 Indian Ocean tsunami. In this preliminary report, results from SEM-EDX analysis for soil sample collected from West Aceh Regency, the closest region to the earthquake epicenter, are presented. SEM image of the tsunami impacted soil sample shows a characteristic morphology with smaller particles and inhomogenous distribution. This is assumed due to the precipitation of several dissolved chemical elements during inundation by the tsunami water. EDX analysis proved that the tsunami impacted soil sample contaminated by organic components such as C and O, alkali/alkaline earth metals (Ca, Mg, Na, and K) as well as transition metals components including Al, Ti, Fe, Si. On the other hand, this experiment also displayed that oxygen element is a dominant element in the tsunami impacted soil with concentration of 52,57%, followed by carbon of 23.37% and silica of 13.41% (wt). The chemical profile of the tsunami impacted soil observed in this work suggests that SEM-EDX technique is a prospective method for evaluation of chemical composition in any impacted soil samples collected from tsunami affected area of Aceh, Indonesia.

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Numerical investigation of Richtmyer–Meshkov instability in shock-driven light square bubble via magnetohydrodynamics

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Computers & Fluids 2025年 299卷

作者： Sheng-Bo Zhang Satyvir Singh Manuel Torrilhon Huan-Hao Zhang Zhi-Hua Chen Chun Zheng National Key Laboratory of Transient Physics Nanjing University of Science and Technology Xiaolingwei 200 210094 Nanjing China Applied and Computational Mathematics RWTH Aachen University Schinkelstrasse 2 52062 Aachen Germany Department of Mathematics Graphic Era Deemed to be University Dehradun Uttarakhand India National Graduate College for Engineers Southern University of Science and Technology Xueyuan Avenue 1008 518055 Shenzhen China School of Energy and Power Engineering Nanjing University of Science and Technology Xiaolingwei 200 210094 Nanjing China

This study presents a numerical investigation of magnetohydrodynamics (MHD) instability in a shock-driven light square bubble, examining the complex interactions at the interface between shocked fluids in the presence of a magnetic field. By incorporating magnetic fields, the dynamics of such instabilities become even more complex, leading to novel behavior in terms of vorticity deposition, mixing, and interface morphology. For numerical simulation, an unsteady compressible ideal magnetohydrodynamics equations in two-dimensional space is solved with the corner transport upwind ＋ constrained transport schemes while preserving the magnetic field’s divergence-free condition. The numerical results show good agreement with the available hydrodynamics experimental data and magnetohydrodynamics calculations. The research results demonstrate that the transverse magnetic field plays a crucial role in the development of MHD-RMI in a light square bubble driven by a planar shock wave. It significantly affects the flow field structure, leading to changes in interface morphology, shock wave structure, vortices and enstrophy. The baroclinic torque induced by magnetic tension at the interface counteracts the torque from velocity shear, thereby inhibiting the roll of Kelvin–Helmholtz vortex. A comprehensive analysis of some physical quantities, including magnetic energy, magnetic strength, and magnetic tension on the square bubble, is presented. MHD-RMI has been found to be a highly effective mechanism for enhancing the magnetic field, thereby improving the suppression of flow instability. Finally, a detailed analysis of the impact of the magnetic field on the time evolution of the interface features is conducted.

关键词： Richtmyer–Meshkov instability MHD Shock wave Light gas interface

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Preliminary report on feasibility of laser induced breakdown spectroscopy (LIBS) coupled with eco-friendly capping material for discriminating heavy metal contaminants in liquid milk

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AIP Conference Proceedings 2023年第1期2480卷

作者： Muliadi Ramli Rara Mitaphonna Febriani Saiful Kurnia Lahna Nasrullah Idris Department of Chemistry Faculty of Mathematics and Natural Sciences Universitas Syiah Kuala Jl. Syech Abdurrauf No. 3 Darussalam 23111 Banda Aceh Aceh Indonesia Doctoral Program of Mathematics and Applied Sciences Universitas Syiah Kuala 23111 Banda Aceh Indonesia Department of Physics Faculty of Mathematics and Natural Sciences Universitas Syiah Kuala Jl. Syech Abdurrauf No. 3 Darussalam 23111 Banda Aceh Aceh Indonesia

This work was carried out to examine the feasibility of LIBS technique coupled with chitosan adsorbent for heavy metal analysis in liquid sample, namely liquid milk products. Heavy metals contained in the liquid products were trapped on the chitosan surface before being irradiated by a focused laser beam using a LIBS technique. Preliminary results of the emission spectra of the heavy metal (Pb) capped on chitosan can clearly be detected using the LIBS technique. Thus, this proposed method of LIBS coupled with chitosan adsorbent could be a promising, efficient and eco-friendly techniques for analyzing heavy metal contaminants in milk liquid samples.

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Uniform local well-posedness and inviscid limit for the Benjamin-Ono-Burgers equation

arXiv

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arXiv 2019年

作者： Chen, Mingjuan Guo, Boling Han, Lijia Institute of Applied Physics and Computational Mathematics Beijing100088 China Department of Mathematics and Physics North China Electric Power University Beijing102206 China

In this paper, we study the Cauchy problem for the Benjamin-Ono-Burgers equation tu-o2 xu+H2 xu+uux = 0, where H denotes the Hilbert transform. We obtain that it is uniformly locally well-posed for small data in the refined Sobolev space eH (R)( > 0), whose low-frequency part is scaling critical and high-frequency part is equal to Sobolev space H( > 0). Furthermore, we also obtain its inviscid limit behavior in eH (R)( > 0).MSC Codes 35Q53, 35Q55, 35A01 Copyright © 2019, The Authors. All rights reserved.

关键词： Sobolev spaces

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Spin-Triplet Excitonic Insulator: The Case of Semihydrogenated Graphene

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Physical Review Letters 2020年第16期124卷 166401-166401页

作者： Zeyu Jiang Wenkai Lou Yu Liu Yuanchang Li Haifeng Song Kai Chang Wenhui Duan Shengbai Zhang State Key Laboratory of Low-Dimensional Quantum Physics and Collaborative Innovation Center of Quantum Matter Department of Physics Tsinghua University Beijing 100084 China SKLSM Institute of Semiconductors Chinese Academy of Sciences P.O. Box 912 Beijing 100083 China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing 100088 China Key Lab of advanced optoelectronic quantum architecture and measurement (MOE) and Advanced Research Institute of Multidisciplinary Science Beijing Institute of Technology Beijing 100081 China CAEP Software Center for High Performance Numerical Simulation Beijing 100088 China Beijing Academy of Quantum Information Sciences Beijing 100193 China Institute for Advanced Study Tsinghua University Beijing 100084 China Department of Physics Applied Physics and Astronomy Rensselaer Polytechnic Institute Troy New York 12180 USA

While various excitonic insulators have been studied in the literature, due to the perceived too-small spin splitting, spin-triplet excitonic insulator is rare. In two-dimensional systems such as a semihydrogenated graphene (known as graphone), however, it is possible, as revealed by first-principles calculations coupled with Bethe-Salpeter equation. The critical temperature, given by an effective Hamiltonian, is 11.5 K. While detecting excitonic insulators is still a daunting challenge, the condensation of triplet excitons will result in spin superfluidity, which can be directly measured by a transport experiment. Nonlocal dielectric screening also leads to an unexpected phenomenon, namely, an indirect-to-direct transition crossover between single-particle band and exciton dispersion in the semihydrogenated graphene, which offers yet another test by experiment.

关键词： Excitons Graphene First-principles calculations

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Warm dense matter simulation via electron temperature dependent deep potential molecular dynamics

arXiv

引用

arXiv 2019年

作者： Zhang, Yuzhi Gao, Chang Zhang, Linfeng Wang, Han Chen, Mohan Center for Applied Physics and Technology HEDPS College of Engineering Peking University Beijing100871 China Beijing Institute of Big Data Research Beijing100871 China Program in Applied and Computational Mathematics Princeton University PrincetonNJ United States Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Huayuan Road 6 Beijing100088 China

Simulating warm dense matter that undergoes a wide range of temperatures and densities is challenging. Predictive theoretical models, such as quantum-mechanics-based first-principles molecular dynamics (FPMD), require a huge amount of computational resources. Herein, we propose a deep learning based scheme, called electron temperature dependent deep potential molecular dynamics (TDDPMD), for efficiently simulating warm dense matter with the accuracy of FPMD. The TDDPMD simulation is several orders of magnitudes faster than FPMD, and, unlike FPMD, its efficiency is not affected by the electron temperature. We apply the TDDPMD scheme to beryllium (Be) in a wide range of temperatures (0.4 to 2500 eV) and densities (3.50 to 8.25 g/cm3). Our results demonstrate that the TDDPMD method not only accurately reproduces the structural properties of Be along the principal Hugoniot curve at the FPMD level, but also yields even more reliable diffusion coefficients than typical FPMD simulations due to its ability to simulate larger systems with longer time. Copyright © 2019, The Authors. All rights reserved.

关键词： Molecular dynamics

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Realization of ultrabroadband THz/IR photoresponse in a bias-tunable ratchet photodetector

arXiv

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arXiv 2021年

作者： Bai, Peng Li, Xiaohong Yang, Ning Chu, Weidong Bai, Xueqi Huang, Siheng Zhang, Yueheng Shen, Wenzhong Fu, Zhanglong Shao, Dixiang Tan, Zhiyong Li, Hua Cao, Juncheng Li, Lianhe Linfield, Edmund Harold Xie, Yan Zhao, Ziran Institute of Applied Physics and Computational Mathematics Beijing100088 China Key Laboratory of Artificial Structures and Quantum Control School of Physics and Astronomy Shanghai Jiao Tong University Shanghai200240 China Key Laboratory of Terahertz Solid-State Technology Shanghai Institute of Microsystem and Information Technology Chinese Academy of Sciences Shanghai200050 China School of Electronic and Electrical Engineering University of Leeds LeedsLS2 9JT United Kingdom Department of Engineering Physics Tsinghua University Beijing100084 China

High performance Terahertz (THz) photodetector has drawn wide attention and got great improvement due to its significant application in biomedical, astrophysics, nondestructive inspection, 6th generation communication system as well as national security application. Here we demonstrate a novel broadband photon-type THz/infrared (IR) photodetector based on the GaAs/AlxGa1-xAs ratchet structure. This kind of photodetector realizes a THz photon-response based on the electrically pumped hot hole injection and overcomes the internal workfunction related spectral response limit. An ultrabroadband photoresponse from 4 THz to 300 THz and a peak responsivity of 50.3 mA/W are realized at negative bias voltage of -1 V. The photodetector also presents a bias-tunable photon-response characteristic due to the asymmetric structure. The ratchet structure also induces an evident photocurrent even at zero bias voltage, which indicates the detector can be regard as a broadband photovoltaic-like detector. The rectification characteristic and high temperature operation possibility of the photodetector are also discussed. This work not only demonstrates a novel ultrabroadband THz/IR photodetector, but also provides a new method to study the light-responsive ratchet. Copyright © 2021, The Authors. All rights reserved.

关键词： Photons

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Superposition and mimicking theorems for conditional McKean-Vlasov equations

arXiv

引用

arXiv 2020年

作者： Lacker, Daniel Shkolnikov, Mykhaylo Zhang, Jiacheng IEOR Department Columbia University New YorkNY10027 United States ORFE Department Bendheim Center for Finance Program in Applied & Computational Mathematics Princeton University PrincetonNJ08544 United States ORFE Department Princeton University PrincetonNJ08544 United States

We consider conditional McKean-Vlasov stochastic differential equations (SDEs), such as the ones arising in the large-system limit of mean field games and particle systems with mean field interactions when common noise is present. The conditional time-marginals of the solutions to these SDEs satisfy non-linear stochastic partial differential equations (SPDEs) of the second order, whereas the laws of the conditional time-marginals follow Fokker-Planck equations on the space of probability measures. We prove two superposition principles: The first establishes that any solution of the SPDE can be lifted to a solution of the conditional McKean-Vlasov SDE, and the second guarantees that any solution of the Fokker-Planck equation on the space of probability measures can be lifted to a solution of the SPDE. We use these results to obtain a mimicking theorem which shows that the conditional time-marginals of an Itô process can be emulated by those of a solution to a conditional McKean-Vlasov SDE with Markovian coefficients. This yields, in particular, a tool for converting open-loop controls into Markovian ones in the context of controlled McKean-Vlasov *** Codes 60H10, 60H15, 35Q84, 93E20 Copyright © 2020, The Authors. All rights reserved.

关键词： Fokker Planck equation

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Unified gas-kinetic wave-particle methods VI: Disperse dilute gas-particle multiphase flow

arXiv

引用

arXiv 2021年

作者： Yang, Xiaojian Liu, Chang Ji, Xing Shyy, Wei Xu, Kun Department of Mechanical and Aerospace Engineering Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong Institute of Applied Physics and Computational Mathematics Beijing China Department of Mathematics Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong Guangdong-Hong Kong-Macao Joint Laboratory for Data-Driven Fluid Mechanics and Engineering Applications Hong Kong University of Science and Technology Hong Kong Shenzhen Research Institute Hong Kong University of Science and Technology Shenzhen Hong Kong

In this paper, a unified gas-kinetic wave-particle scheme (UGKWP) for the disperse dilute gas-particle multiphase flow is proposed. In this study, the gas phase is always in the hydrodynamic regime. However, the particle phase covers different flow regimes from particle trajectory crossing to the hydrodynamic wave interaction with the variation of local particle phase Knudsen number. The UGKWP is an appropriate method for the capturing of the multiscale transport mechanism in the particle phase through its coupled wave-particle formulation. In the regime with intensive particle collision, the evolution of solid particle will be followed by the analytic wave with quasi-equilibrium distribution;while in the rarefied regime the non-equilibrium particle phase will be captured through particle tracking and collision, which plays a decisive role in recovering particle trajectory crossing behavior. The gas phase in the multiphase system is assumed to be stay in the continuum flow regime, and its evolution is mainly controlled by the Navier-Stokes equations with the interaction with particle phase. The gas-kinetic scheme (GKS) is employed for the simulation of gas flow. In the highly collision regime for the particles, no particles will be sampled in UGKWP and the wave formulation for solid particle with the hydrodynamic gas phase will reduce the system to the two-fluid Eulerian model. On the other hand, in the collisionless regime for the solid particle, the free transport of solid particle will be followed in UGKWP, and coupled system will return to the Eulerian-Lagrangian formulation for the gas and particle. The scheme will be tested for in all flow regimes, which include the non-equilibrium particle trajectory crossing, the particle concentration under different Knudsen number, and the dispersion of particle flow with the variation of Stokes number. A experiment of shock-induced particle bed fluidization is simulated and the results are compared with experimental measu

关键词： Gases

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