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Dynamics of antipolar distortions

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npj Computational Materials 2017年第1期3卷 171-178页

作者： Kinnary Patel Sergey Prosandeev laurent bellaiche Physics Department and Institute for Nanoscience and Engineering University of ArkansasFayettevilleAR 72701USA Institute of Physics and Physics Department of Southern Federal University Rostov-na-Donu 344090Russia

Materials possessing antipolar cation motions are currently receiving a lot of attention because they are fundamentally intriguing while being technologically *** studies devoted to these complex materials have focused on their static properties or on their zone-center *** a result,some important dynamics of antipolar cation distortions,such as the temperature behavior of their phonon frequencies,have been much less investigated,despite the possibility to exhibit unusual ***,we report the results and analysis of atomistic simulations revealing and explaining such dynamics for BiFeO3 bulks being subject to hydrostatic *** is first predicted that cooling such material yields the following phase transition sequence:the cubic paraelectric Pm3m state at high temperature,followed by an intermediate phase possessing long-range-ordered in-phase oxygen octahedral tiltings,and then the Pnma state that is known to possess antipolar cation motions in addition to in-phase and antiphase oxygen octahedral *** cation modes are found to all have high phonon frequencies that are independent of temperature in the paraelectric *** the other hand and in addition to antipolar cation modes increasing in number,some phonons possessing antipolar cation character are rather soft in the intermediate and Pnma *** of our data combined with the development of a simple model reveals that such features originate from a dynamical mixing between pure antipolar cation phonons and fluctuations of oxygen octahedral tiltings,as a result of a specific trilinear energetic *** developed model can also be easily applied to predict dynamics of antipolar cation motions for other possible structural paths bringing Pm3m to Pnma states.

关键词： polar distortion phonon

Strain engineering of electro-optic constants in ferroelectric materials

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npj Computational Materials 2019年第1期5卷 1092-1096页

作者： Charles Paillard Sergei Prokhorenko laurent bellaiche Department of Physics and Institute for Nanoscience and Engineering University of ArkansasFayettevilleAR 72701USA

Electro-optic effects allow control of the ow of light using electric fields,and are of utmost importance for today’s information and communication technologies,such as TV displays and fiber *** search for large electro-optic constants in films is essential to the miniaturization and increased efficiency of electro-optic *** this work,we demonstrate that strain-engineering in PbTiO_(3) films allows to selectively choose which electro-optic constant to *** electro-optic constants larger than 100 pm V^(−1) are predicted,either by driving the softening of an optical phonon mode at a phase transition boundary under tensile strain,or by generating the equivalent of a negative pressure via compressive strain to obtain large piezoelectric *** particular,a r_(13) electro-optic coefficient twice as large as the one of the commonly used LiNbO_(3) electro-optic material is found here when growing PbTiO_(3) on the technologicallyimportant Si substrate.

关键词： softening constants ferroelectric

Interplay between Kitaev interaction and single ion anisotropy in ferromagnetic CrI_(3) and CrGeTe_(3) monolayers

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npj Computational Materials 2018年第1期4卷 185-190页

作者： Changsong Xu Junsheng Feng Hongjun Xiang laurent bellaiche Physics Department and Institute for Nanoscience and Engineering University of ArkansasFayettevilleAR 72701USA Key Laboratory of Computational Physical Sciences(Ministry of Education) State Key Laboratory of Surface Physicsand Department of PhysicsFudan University200433 ShanghaiChina School of Physics and Materials Engineering Hefei Normal University230601 HefeiChina Collaborative Innovation Center of Advanced Microstructures 210093 NanjingChina

Magnetic anisotropy is crucially important for the stabilization of two-dimensional(2D)magnetism,which is rare in nature but highly desirable in spintronics and for advancing fundamental *** works on CrI3 and CrGeTe_(3) monolayers not only led to observations of the long-time-sought 2D ferromagnetism,but also revealed distinct magnetic anisotropy in the two systems,namely Ising behavior for CrI3 versus Heisenberg behavior for CrGeTe_(3).Such magnetic difference strongly contrasts with structural and electronic similarities of these two materials,and understanding it at a microscopic scale should be of large ***,firstprinciples calculations are performed and analyzed to develop a simple Hamiltonian,to investigate magnetic anisotropy of CrI3 and CrGeTe_(3) *** anisotropic exchange coupling in both systems is surprisingly determined to be of ***,the interplay between this Kitaev interaction and single ion anisotropy(SIA)is found to naturally explain the different magnetic behaviors of CrI3 and CrGeTe_(3).Finally,both the Kitaev interaction and SIA are further found to be induced by spin–orbit coupling of the heavy ligands(I of CrI3 or Te of CrGeTe_(3))rather than the commonly believed 3d magnetic Cr ions.

关键词： anisotropy interaction coupling

Large scale hybrid Monte Carlo simulations for structure and property prediction

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npj Computational Materials 2018年第1期4卷 1-7页

作者： Sergei Prokhorenko Kruz Kalke Yousra Nahas laurent bellaiche Physics Department and Institute for Nanoscience and Engineering University of ArkansasFayettevilleAR 72701USA

The Monte Carlo method is one of the first and most widely used algorithms in modern computational *** condensed matter physics,the particularly popular flavor of this technique is the Metropolis Monte Carlo *** being incredibly robust and easy to implement,the Metropolis sampling is not well-suited for situations where energy and force evaluations are computationally *** search for a more efficient technique,we here explore the performance of Hybrid Monte Carlo sampling,an algorithm widely used in quantum electrodynamics,as a structure prediction scheme for systems with long-range *** results show that the Hybrid Monte Carlo algorithm stands out as an excellent computational scheme that can not only significantly outperform the Metropolis sampling but also complement molecular dynamics in materials science applications,while allowing ultra-large-scale simulations of systems containing millions of particles.

关键词： prediction property scheme

Strain-induced resonances in the dynamical quadratic magnetoelectric response of multiferroics

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npj Computational Materials 2020年第1期6卷 1156-1161页

作者： S.Omid Sayedaghaee Charles Paillard Sergey Prosandeev Bin Xu laurent bellaiche Physics Department and Institute for Nanoscience and Engineering University of ArkansasFayettevilleArkansas 72701USA Microelectronics-Photonics Program University of ArkansasFayettevilleArkansas 72701USA Laboratoire Structures Propriétés et Modélisation des SolidesCentraleSupélecCNRS UMR 8580UniversitéParis-Saclay91190 Gifsur-YvetteFrance Institute of Physics and Physics Department of Southern Federal University Rostov-na-Donu 344090Russia School of Physical Science and Technology Soochow UniversitySuzhouJiangsu 215006China

For the last few years,the research interest in magnetoelectric(ME)effect,which is the cross-coupling between ferroelectric and magnetic ordering in multiferroic materials,has experienced a significant *** extensive recent studies are not only conducted towards the design of sensors,actuators,transducers,and memory devices by taking advantage of the cross-control of polarization(or magnetization)by magnetic(or electric)fields,but also aim to create a clearer picture in understanding the sources of ME responses and the novel effects associated with *** we derive analytical models allowing to understand the striking and novel dynamics of ME effects in multiferroics and further confirm it with atomistic ***,the role of strain is revealed to lead to the existence of electroacoustic magnons,a new quasiparticle that mixes acoustic and optical phonons with magnons,which results in resonances and thus a dramatic enhancement of magnetoelectric ***,a unique aspect of the dynamical quadratic ME response under a magnetic field with varying frequencies,which is the second harmonic generation(SHG),has not been discussed prior to the present *** SHGs put emphasis on the fact that nonlinearities should be considered while dealing with such systems.

关键词： quadratic dynamical resonance

Tailoring properties of hybrid perovskites by domain-width engineering with charged walls

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npj Computational Materials 2018年第1期4卷 26-31页

作者： Lan Chen Charles Paillard Hong Jian Zhao JorgeÍñiguez Yurong Yang laurent bellaiche Physics Department and Institute for Nanoscience and Engineering University of ArkansasFayettevilleArkansas 72701USA Materials Research and Technology Department Luxembourg Institute of Science and Technology(LIST)5 Avenue des Hauts-FourneauxL-4362 Esch/AlzetteLuxembourg National Laboratory of Solid State Microstructures Jiangsu Key Laboratory of Artificial Functional Materials and Collaborative Innovation Center of Advanced MicrostructuresNanjing UniversityNanjing 210093China

Charged ferroelectric domain walls are fascinating electrical topological defects that can exhibit unusual ***,in the search for novel phenomena,we perform and analyze first-principles calculations to investigate the effect of domain width on properties of domains with charged walls in the photovoltaic material consisting of methylammonium lead iodide hybrid *** report that such domains are stable and have rather low domain wall energy for any investigated width(that is,up to 13 lattice constants).Increasing the domain width first linearly decreases the electronic band gap from≃1.4 eV to about zero(which therefore provides an efficient band-gap engineering),before the system undergoes an insulator-to-metal transition and then remains metallic(with both the tail-to-tail and head-to-head domain walls being conductive)for the largest *** these results can be understood in terms of:(i)components of polarization along the normal of the domain walls being small in magnitude;(ii)an internal electric field that is basically independent of the domain width;and(iii)rather negligible charge transfer between *** findings deepen the knowledge of charged ferroelectric domain walls and can further broaden their potential for applications,particularly in the context of halide perovskites for photovoltaics.

关键词： properties walls perovskite

Prediction of room-temperature half-metallicity in layered halide double perovskites

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npj Computational Materials 2019年第1期5卷 132-139页

作者： Jian Xu Changsong Xu Jian-Bo Liu laurent bellaiche Hongjun Xiang Bai-Xin Liu Bing Huang Key Laboratory of Advanced Materials(MOE) School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China Beijing Computational Science Research Center Beijing 100193China Physics Department and Institute for Nanoscience and Engineering University of ArkansasFayettevilleAR 72701USA Key Laboratory of Computational Physical Sciences(Ministry of Education) State Key Laboratory of Surface Physicsand Department of PhysicsFudan UniversityShanghai 200433China

Half-metallic ferromagnets(HMFs)that possess intriguing physical properties with completely spin-polarized current are key candidates for high-efficiency spintronic ***,HMFs that could simultaneously have high Curie temperature(Tc),wide half-metallic gap(ΔHM),and large bulk magnetocrystalline anisotropy energy(MAE)are very rare,which significantly restrict their room-temperature(RT)*** this article,through materials screening in layered halide double perovskites(LHDPs).

关键词： metallic perovskite halide

Author Correction:Strain engineering of electro-optic constants in ferroelectric materials

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npj Computational Materials 2019年第1期5卷 254-255页

作者： Charles Paillard Sergei Prokhorenko laurent bellaiche Department of Physics and Institute for Nanoscience and Engineering University of ArkansasFayettevilleAR 72701USA

After publishing this article,we realized that the calculation of the piezoelectric constants dij by Density Functional Perturbation Theory(DFPT),as explained in the methods described in the original version of the Supplementary Information,are incorrect in the case of a partially clamped *** correct methodology is to inverse the subspace matrix of elastic constants.

关键词： constants ferroelectric piezoelectric