Track D
Computer Modelling and Simulation of Material Properties
ABSTRACTS
Session D-1 Materials for electronics, opto-electronics and photonics (including organic and inorganic semiconductors, halide perovskites, layered materials, soft and bio materials)
D-1:IL01 Role of the Trap-assisted Auger-Meitner Effect in Nonradiative Recombination
F. Zhao, M. Turiansky, C.G. Van de Walle, Materials Department, University of California, Santa Barbara, CA, USA
Defect-assisted nonradiative recombination limits the efficiency of optoelectronic devices. First-principles calculations have elucidated the fundamental processes in solid-state light emitters emitting at green and longer wavelengths. However, the traditional mechanism based on multiphonon emission fails to account for sources of loss in wider-band-gap materials emitting in the blue or ultraviolet. This puzzle can be resolved by taking into account trap-assisted Auger-Meitner recombination, which enables capture by exciting a carrier to a higher-energy state. We have developed a practical first-principles methodology to determine the trap-assisted Auger-Meitner recombination rate for defects and impurities in semiconductors [1]. As a test case, we focused on a calcium substitutional impurity in InGaN, where inclusion of trap-assisted Auger results in recombination rates orders of magnitude larger than the recombination rate governed by multiphonon emission alone. Our computational formalism is general and can be applied to any defect or impurity in any semiconducting or insulating material. We acknowledge the late Audrius Alkauskas for his invaluable contributions.
[1] F. Zhao, M. E. Turiansky, A. Alkauskas, and C. G. Van de Walle, Phys. Rev. Lett. 131, 056402 (2023).
D-1:IL02 Van der Waals Interactions in Materials Modelling
A. TKATCHENKO, Department of Physics and Materials Science, University of Luxembourg, Luxembourg
Noncovalent van der Waals (vdW) or dispersion forces are ubiquitous in nature and influence the structure, stability, dynamics, and function of molecules and materials throughout chemistry, biology, physics, and materials science. These forces are quantum mechanical in origin and arise from electrostatic interactions between fluctuations in the electronic charge density. This lecture will discuss the mathematical and physical concepts, methodology, and practice for treating the ubiquitous vdW interactions in materials modeling. We will discuss a common framework [Adv. Funct. Mater. 25, 2054 (2015); Chem. Rev. 117, 4714 (2017); Science 351, 1171 (2016)] for understanding all existing vdW-enabled density functionals, show their strengths and limits, and conclude with many challenges that remain towards the development of a universal vdW methodology, which will be able to deliver accurate and robust insights into physical, chemical, and biological systems.
D-1:IL03 Controlling Spin by Materials Design in Light-emitting Applications: A Computational Perspective
Y. OLIVIER, University of Namur, Namur Institute of Structured Matter, Namur, Belgium
Organic light-emitting diodes (OLEDs) efficiencies are tightly bound with the spin statistics of charge recombination which for conventional fluorescent materials results in a balance of one emissive singlet to three lost to heat triplets. Therefore, the internal quantum efficiency (IQE) is limited to 25% in this class of materials. Different strategies to design fully organic light-emitting materials including thermally activated delayed fluorescence (TADF), inverted singlet-triplet gap materials (INVEST) as well as doublet radical emitters were proposed allowing in theory to reach 100% IQE. In this communication, we will discuss the optoelectronic properties of these different classes of materials based on computational considerations. Especially: - We will discuss how doped triangle-shaped molecules lead to (i) concomitant narrow emission, high quantum yield of emission and small singlet-triplet gap EST resulting in multi-resonant TADF emitters and to (ii) INVEST materials leading potentially to a downwards energy reverse intersystem crossing (RISC). - We will show how the optoelectronic properties of organic radical materials are tuned to lead to either red emitters for OLEDs or materials with optically accessible high spin state for quantum information applications.
D-1:IL04 MOMAP: A Computational Software for Molecular Materials for Optoelectronic Property
ZHIGANG SHUAI, School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, China
We will first present a home-built software MOMAP, which can be used to computing organic light-emitting efficiency and linewidth and carrier mobility from first principles. Localization and scattering relaxation dominate the transport processes. We will discuss the role of localization, quantum nuclear tunneling, and off-diagonal disorder. We further discuss the spin-phonon interaction on the spin current for chiral molecular wires via the time-dependent density matrix renormalization group theory.
D-1:L05 On the Nature of Oxygen Vacancies in Amorphous Alumina
A. SHLUGER1, 2, J. Strand1, 3, 1Department of Physics and Astronomy, University College London, London, UK; 2WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai, Japan; 3Nanolayers Research Computing Ltd., London, UK
The nature and properties of oxygen vacancies in amorphous (a)-Al2O3 and other amorphous oxides is a fundamental issue for many applications. Modeling defects in amorphous solids has been often carried out by analogy with their crystalline counterparts. To overcome some of the limitations of previous simulations, we have used ab-initio Molecular Dynamics (AIMD) with a non-local density functional to model the electronic properties of oxygen-deficient amorphous alumina. The melt-and-quench simulations of periodic models and high-temperature anneal simulations of amorphous models with pre-existing oxygen vacancies both demonstrate the existence of stable deep defect states associated with oxygen deficiency. Apart from point defects structurally similar to oxygen vacancies in the crystal phase, we show the formation of more stable defect states characterized by the bond formation between under-coordinated Al ions. Thus, a point defect, is still a meaningful concept in disordered systems, but some configurations do not have the same meaning as a crystallographic defect. Our results illustrate the sensitivity of these predictions to the choice of computational parameters mainly caused by the polaronic character of the electron localization accompanying this defect formation.
D-1:IL07 Novel Electronic, Excitonic, and Optical Features in 2D and 1D Lead-halide Hybrid Perovskites via Tuning of the Electronic Couplings between Organic Spacers and Inorganic Layers
HONG LI, The University of Arizona, Tucson, AZ, USA
Two-dimensional (2D) lead-halide perovskites have drawn great interest due to their improved photo-stability and chemical stability in comparison to their three-dimensional (3D) counterpart. In the past few years, increasing efforts have been made in tuning the chemical nature of the organic spacers in the 2D perovskites for their applications as light-emitting or photovoltaic materials. However, most of these efforts have focused on investigating the inorganic-inorganic or organic-organic interactions while overlooking an interesting feature that could be induced by generating significant electronic couplings between the frontier molecular orbitals of the organic cations and the band edge states of the inorganic framework. Such a strong coupling between the organic and inorganic components may lead to novel electronic, excitonic, and optical properties that can further broaden the perovskite materials applications. In this talk, I will discuss our recent work investigating the novel electronic and excitonic behaviors induced by the electronic couplings between the inorganic perovskite layers and π-conjugated organic spacer layers in 2D and 1D halide perovskites.
D-1:IL08 Unveiling the Optical and Electronic Properties of Dimensionally Confined Halide Perovskites with Ab-initio Simulations
C. QUARTI, University of Mons, Mons, Belgium
Metal halide perovskites are swiftly emerging as ideal candidates for opto-electronic applications. Their dimensionally confined analogues in particular present a broad range of functionalities, thanks to a unique set of features, like quantum confinement, enhanced many body interactions, formation of stable excitons, etc. Along with their unparalleled compositional flexibility, as related to the huge library of organic spacers available, these materials are becoming more and more interesting for technologic applications. Here, we show how ab-initio simulations can contribute to build a sounded knowledge of the electronic and optical properties of these hybrid materials. We combine the ab-initio solution of the Bethe-Salpeter equation with symmetry analysis to characterise the optical properties of these materials. Namely, we assign the excitonic progression of these compounds, including the exciton fine structure and spin-properties, fully accounting for relativistic spin-orbit-coupling. Furthermore, we discuss the electronic properties of these materials, with special focus on the interactions in the out-of-plane direction, setting a sounded understanding based on simplified, symmetric models, then extending to a series of compounds reported experimentally.
D-1:L09 A Feedback Model for Relaxor Ferroelectrics
H. KLIEM, A. Leschhorn, Saarland University, Saarbruecken, Germany
Relaxor ferroelectric ceramics and also relaxor organic materials exhibit unusually high dielectric permittivities in a broad temperature T range. The relaxation times display in an Arrhenius plot a nonlinear curve, i.e. a Vogel-Fulcher law, instead of a straight line. By cooling down from high T, relaxors don't show a spontaneous polarization P, unless they are subjected to high electrical fields. The hysteresis loop of P can turn into double loops in restricted T ranges. The model developed is based on interacting charges or polar nanoregions fluctuating thermally activated in asymmetric double well potentials. The intrinsic asymmetries are caused by disorder in the material and evoke the relaxor behaviour. For ordered systems with symmetrical double wells a ferroelectric behaviour is found. The electrostatic interaction is considered by a mean field approach according to Weiss. The local fields at the double wells are given by the applied field and a feedback field proportional to P. The transition rates in the double wells are altered by P and a feedback loop appears. We compute high permittivities in a broad T range and a Vogel-Fulcher law. At low T a hysteresis of P arises, which turns into a double loop for high T and finally degrades. No spontaneous polarization appears.
D-1:L10 The Topological Design of Exceptional Points for Multi-optical-parameter Control based on Deep Learning
CHANGZHI GU, PENG FU, Institute of Physics, Chinese Academy of Sciences, Beijng, China
The structure design is the core of micro-nanophotonic devices and optical systems. Many artificially designed photonic structures, such as metamaterials, photonic crystals, and plasmonic nanostructures, have been widely used in high-speed visible communication, high-sensitivity sensing, and efficient energy harvesting and conversion. The deep learning (DL) has been developed rapidly in fields such as language recognition, machine vision, and natural language processing in the past few years. The unique advantage of DL lies in its data-driven algorithm, which allows models for discovering useful information from massive amounts of data automatically and provides a new route to solve the aforementioned design problems of photonic structures. Leveraging deep learning, we observe topological charge conservation and utilize the topologically protected optical parameter distribution around scattered Exceptional points (EPs). Based on these, we introduce amplitude-phase multiplexing and wavelength division multiplexing devices. Our work allows rapid and precise discovery of EPs topology, offers a powerful tool for digging related physics, and provides a paradigm for multi-optical parametric manipulation with high performance and less crosstalk.
D-1:IL11 Large-scale Nonadiabatic Dynamics Methods and Applications to Quantum Dots
LINJUN WANG, Department of Chemistry, Zhejiang University, Hangzhou, China
In chemistry, physics, biology, and material sciences, many important processes belong to non-adiabatic dynamics. In particular, electron and exciton long-range dynamics involve a large number of electronic states and vibrational degrees of freedom, and thus quantum decoherence and complex surface crossings should be properly described. In the past years, we have proposed a series of methods for large-scale nonadiabatic dynamics. The trajectory branching methods systematically improve the accuracy, while the surface hopping methods without explicitly using nonadiabatic couplings significantly enhance the efficiency. Based on Wannier analysis and machine learning, a divide-and-conquer approach realizes efficient electronic structure calculations. We studied quantum-dot/polymer interfaces and found anomalous charge transfer across a large energy barrier of 0.5 eV, which is dominated by energetic disorder, polaron, and entropy effects. We reveal that electron leakage is key for green and blue quantum dot light-emitting diodes and achieve the theoretical limit of efficiency by material design. The absorption and emission spectra of quantum dots were obtained and compared with experiment. Simulation of the oxidation dynamics in large quantum dots was also realized.
D-1:IL13 Progress in Multiphysics Modelling of Nano-photonics Components based on Phase Change Materials
D.N. CHIGRIN, DWI Leibniz Institute for Interactive Materials, Aachen, Germany, I. Physikalisches Institut (1A), RWTH Aachen University, Aachen, Germany
Phase change materials undergo rapid and reversible phase transition, resulting in significant changes of their physical properties. These materials have enormous technological potential, with applications ranging from neuromorphic devices and efficient high-frequency electronics to (re)programmable optical metamaterials and integrated photonics. However, it is a long and iterative empirical process to systematically analyse and optimise material properties. The incorporation of computational methods into materials design offers an encouraging prospect for simplifying and optimising the design process, which in turn could reduce the time and cost associated with achieving desired material properties. The implementation of computational techniques for materials design significantly reduces the resource and time requirements, thereby promoting advanced product development in a wide range of fields. Progress towards a unified description of complex nanophotonic devices based on phase change materials is presented. This description requires a self-consistent analysis of electromagnetic, heat transfer, carrier transport and phase transition models. The potential applications of such a multiphysics approach in the realms of metamaterials and nanophotonics are explored and discussed.
D-1:L14 Charge and Exciton Dynamics in the Transient Delocalization Regime
S. GIANNINI, G. Prampolini, F. Santoro, Institute of Chemistry of OrganoMetallic Compounds, National Research Council (ICCOM-CNR), Pisa, Italy; J. Blumberger, University College London, Department of Physics and Astronomy, Gower Street, London, UK; D. Beljonne, Laboratory for Chemistry of Novel Materials, University of Mons, Mons, Belgium
The transport of charges and excitons in molecular systems is crucial for the operation of flexible optoelectronic devices like organic solar cells and field-effect transistors. However, it is remarkable that the nature of charges and excitons, along with the related transport mechanisms in these soft materials, has puzzled the community for many years. Even in seemingly simple systems, e.g., organic single crystals, some experiments seem to favor a localized particle picture, while others support a coherent wave-like interpretation. Our atomistic non-adiabatic molecular dynamics simulations reveal that charge and energy carriers in molecular and polymeric semiconductors are neither waves nor particles. By solving the coupled nuclear-electronic motion, we observe that charges [1] and excitons [2] undergo a transient quantum delocalization mechanism by thermally and momentarily accessing vibrationally dressed extended states. This leads to spatial displacements of the wavefunction in these materials and underlines their temperature-dependent mobility [3]. Designs rules and directions to improve diffusivity will be discussed.
[1] Giannini et al. Nat. Commun. 10, 3843 (2019)
[2] Giannini et al. Nat. Commun. 13, 2755 (2022)
[3] Giannini et al. Nat. Mat (2023), just accepted
Session D-2 Energy generation and storage (including materials for supercapacitors, photovoltaics, thermoelectrics, ferroelectrics, piezoelectrics, batteries, osmosis, fuel cells, thermal energy)
D-2:IL01 Interfacing Doped Graphene with Metal Surfaces or Molecular Layers
C. DI VALENTIN, D. Perilli, Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Milano, Italy
Interesting structural and electronic effect are observed when electronically or chemically doped graphene is interfaced to metal surfaces or molecular layers. In this talk we review some examples that have been simulated in our group by means of density functional theory (DFT) calculations and compared to experimental results: N-doped graphene is interfaced with Ni(111) [1], B-doped graphene is interfaced with Ir(111) [2] and Ni(111) [3], p-type doped graphene is interfaced with a nickel-phthalocyanine (NiPc) monolayer [4] or functionalized with tetrazine [5].
[1] “Inside out” growth method for high-quality nitrogen-doped Graphene. Carbon 171 (2021) 704-710
[2] “Spatial segregation of substitutional B atoms in graphene patterned by the moiré superlattice on Ir(111)” Carbon 201 (2023) 881–890
[3] in preparation
[4] “π-Orbital mediated charge transfer channels in a monolayer Gr–NiPc heterointerface unveiled by soft X-ray electron spectroscopies and DFT calculations” Nanoscale 14 (2022) 13166
[5] “Pushing Down the Limit of NH3 Detection of Graphene-Based Chemiresistive Sensors through Functionalization by Thermally Activated Tetrazoles Dimerization” ACS Nano 16 (2022) 10456−10469
D-2:IL02 Property Analysis and Simulation Package for Materials (PASP) and its Applications to Ferroic Materials
HONGJUN XIANG, Department of Physics, Fudan university, Shanghai, China
We have developed a software package, namely, PASP (Property Analysis and Simulation Package for materials), to analyze the structural, electronic, magnetic, and thermodynamic properties of complex condensed matter systems. Our package integrates several functionalities including group theory analysis, global structure searching methods, tight-binding approach, machine learning algorithms, effective Hamiltonian methods, Monte Carlo simulation, and spin-lattice dynamic simulation methods. In conjunction with first-principles calculations, PASP has been successfully applied to diverse physical systems. For example, we predict that a Pb-free hybrid organic-inorganic perovskite N(CH3)4SnI3 with non-polar molecular cation has strong ferroelectricity, find that there may exist high-order spin interactions in 2D materials, propose a general theory for bilayer stacking ferroelectricity, propose the concept of unconventional ferroelectricity in violation of Neumann's principle.
D-2:L03 Predicting Solar Cell Efficiency from First Principles
XINWEI WANG1, S.R. Kavanagh1, A. WALSH1, 2, 1Thomas Young Centre and Department of Materials, Imperial College London, London, UK; 2Department of Physics, Ewha Womans University, Seoul, South Korea
Theoretical prediction of conversion efficiency accelerates the screening of promising candidates and avoids trial-and-error experiments. So far, most theoretical approaches of efficiency prediction have focused on optoelectronic properties of perfect materials (radiative limit). However, nonradiative recombination of electrons and holes mediated by defects often greatly degrades the performance and thus is an important factor to consider for accurate prediction. In this talk, I will present a computational method which includes both radiative and nonradiative processes to predict the maximum conversion efficiency of imperfect crystals from first principles calculations. I will first introduce the theory and workflow of this method, as well as a comparison of other prediction approaches. Then I will illustrate the method by a class of emerging light absorbers, antimony chalcogenides (Sb2X3, X=S, Se). Sb2X3 have promising electronic and optical properties, but the record conversion efficiency is far from optimal (~10%) and the origin of the bottleneck remains unclear. I will show the extent to which thickness-dependent optical absorption and intrinsic point defects limit the efficiency in Sb2X3. Potential strategies to improve the efficiency in Sb2X3 will also be discussed.
D-2:L04 Capturing the Lone Pair Interactions in BaSnF4 using Machine Learning Potential
XILIANG LIAN1, M. Salanne1, 2, 3, 1Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, France; 2Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459, Amiens Cedex, France; 3Institut Universitaire de France (IUF), Paris, France
Machine learning potential (MLP) has emerged as a promising method to approach the potential energy surface with high accuracy and efficiency. However, the versatility and efficiency of such a method compared with classical interaction potential are rarely investigated. Using BaSnF4, a prospective solid electrolyte for fluoride ion batteries, and an auxiliary simpler system NaF, which holds a rock salt structure, we show how an MLP can capture the subtle interactions of Sn lone pairs while a polarizable force field fails. The accuracy of our MLP is validated by comparing vibrational properties such as phonon dispersion and equation of states with the results obtained from density functional theory and it demonstrates excellent agreement with density functional theory. The MLP also exhibits significantly boosted computational efficiency compared with the reference ab initio molecular dynamics method. Furthermore, from large-scale machine learning molecular dynamics simulation with BaSnF4, we investigated the two-dimensional fluoride ion motion between Ba-Sn and Sn-Sn layers and showed how Sn atoms modulate the fluoride ion diffusivity.
D-2:IL07 Modeling Organic Semiconductors from Low Doping to Ultra-high Charge Densities
G. D'AVINO, Institut Néel, CNRS, Grenoble, France
Molecular doping is arguably the main technique to control charge carriers’ density and transport properties in organic conjugated materials, enabling a variety of technological applications from optoelectronics to thermoelectricity. This talk reports on our multiscale modelling research efforts towards a comprehensive understanding of the mechanism of molecular doping from infinite dilution to high densities. Our message is threefold: (i)We shed light onto the factors controlling the energetics of the ionization of dopant impurities, putting emphasis on the relationship between nanostructure and electronic properties.[1] (ii)We unveil the effect of collective screening phenomena that play a crucial role in the release of Coulombically bound carriers and in the establishment of conducting states upon increasing dopants density.[2] (iii)We finally address the high-doping regime in conjugated polymers. Here, our simulations predict charge transport to be independent on the Coulomb fields of dopant ions, but rather controlled by structural disorder and carriers’ interactions,[3] possibly resulting in emergent non-equilibrium transport phenomena.
[1] Mater.Horiz. 6, 107 (2019); J.Mater.Chem. C 10, 13815 (2022)
[2] Adv.Mater. 34, 2105376 (2022)
[3] J.Am.Chem.Soc. 144, 3005 (2022)
D-2:IL08 Modelling of Energy Storage and Optoelectronic Properties in Organic Molecular Materials
F. NEGRI, Department of Chemistry "Giacomo Ciamician", University of Bologna, Italy and INSTM, UdR Bologna, Italy
Modeling is fundamental to understand and harness the potential of organic molecules for developing novel materials for sustainable energy storage and optoelectronic technologies . In this presentation I will summarize our most recent results in the following major areas. First, I will discuss key aspects of the optoelectronic properties of conjugated chromophores displaying diradical character, which are building blocks for promising functional materials. On one hand we have shown that full absence of emission can lead to highly efficient light to- heat conversion of the absorbed radiation with outstanding photo-thermal conversion. On the other hand, we have demonstrated unexpected luminescence properties for paraquinodimethane derivatives. I will then summarize our recent results on charged species derived from conjugated diradicals. The charged forms of π-conjugated molecules are the microscopic particles transported in the semiconductor component in electrical devices, in energy storage substrates and in organic batteries. However, the number of molecules able to stabilize anions and cations on identical π-conjugated molecular skeletons is small. I will show how conjugated diradicals can overcome this limit.
D-2:IL09 Electrochemical Energy Storage Material Design through Regulating Local Structure Properties
JIANJUN LIU, Integrated Computational Materials Scientific Research Center, Shanghai institute of Ceramics, Chinese Academy of Sciences, Shanghai, China
The relationship for material composition-structure effect on property is a fundamental base for designing new materials and optimizing material performance. In this talk, taking electrochemical storage material as an example, the comprehensive methods including first-principles calculations, machine-learning methods, and electrochemical experimental characterizations were used to study the relationship between local structure property and electroactivity, and reveal local structure electronegativity/electron affinity as screening and design rule of electrocatalyst and electrodes. Putting it in hydrogen evolution electrocatalyst in fuel cell, we computationally predict three-atom doped two-dimension catalyst 3Co-V-MoS2 which can effectively reduce overpotential. The local structure property is also applied in design charge reaction catalyst of Li-O2 battery. Electrochemical experiments show that computational predicting spinel MnCo2O4 has high catalytic activity with 0.3 V overpotential and 400 cycles. The local structure electronegativity is also used to screen Li-S cathode materials for suppressing LiPSs shutting effect from cathode to anode. Not limited for these, the local structure properties are used to design organic electrodes and Li-rich cathodes with experiment.
Session D-3 Quantum information science (including defective solids, superconducting systems, trapped ions, magnets, molecular systems, topological defects)
D-3:IL01 Modelling Adatom Defects in Van der Waals Material Flakes: Interfacing Quantum Optics with Material Science
D. Dams, C. Rockstuhl, Karlsruhe Institute of Technology, Karlsruhe, Germany; G.W. Bryant, Joint Quantum Institute, University of Maryland and National Institute of Standards and Technology, Gaithersburg, MD, USA; A. Ayuela, Centro de Fısica de Materiales and Donostia International Physics Center, San Sebastian, Spain; A. Ghosh, J. Szczuczko, M. Pelc, K. Slowik, Nicolaus Copernicus University in Torun, Torun, Poland
2D material nanoflakes have unique electronic, optical, and material properties determined by their chemical composition and geometry. They can be used as elementary building blocks in heterostructures realising nanoscaled optoelectronics. They may support topological properties or plasmonic optical responses. The latter can be tuned by electronic or optical means or in the presence of atomic defects (adatoms) [1]. In reverse, a flake can be exploited to modulate the dynamics of adatoms positioned in its vicinity [2]. To study these properties, we have developed a theoretical framework and a related toolbox in Python called GRANAD (Graphene Nanoflakes with ADatoms). The framework combines a tight-binding approach to model the electronic properties of nanoflakes with the master equation approach to capture electron dynamics. Originally developed to model graphene, the code has recently been extended to include different 2D materials and their stacks. In the talk, I will discuss the capabilities of the GRANAD toolbox and the selected results we have obtained in the context of quantum information processing. In particular, coupling multiple defects to the flakes allows one to tune their interaction strength, e.g., by modulating the electric carrier density with electric voltage.
D-3:L02 Cluster Dynamics Modeling Study of Irradiation-induced Microstructural Evolution in Tungsten
S. MOHAMED, Q. Yuan, E. Gaganidze, J. Aktaa, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany; J. GAO, Fudan University, Yangpu District, Shanghai, China
The hostile conditions in a fusion tokamak reactor poses the main challenge in the development and design of in-vessel components such as divertor and breeding blanket due to fusion relevant irradiation conditions (14 MeV) and large thermal loads. Neutron irradiation leads to the degradation of the mechanical and thermo-physical properties due to the formation of irradiation-induced microstructural defects such as transmutation products, dislocation loops, and vacancy clusters. In the current study, integrated computational-experimental approach is employed to study the microstructure evolution of dislocation loops and voids in tungsten. Cluster dynamics model is employed and simulations are performed on the irradiated tungsten specimen used in the experimental test. The dpa rate and cascade overlap rate are obtained from the experiments and neutronics simulation, respectively and are implemented in the cluster dynamics model. Based on the comparison between experimental and computational results, the cluster dynamics model provides insights on the evolution of dislocation loops and voids at various temperatures (400oC – 1000oC) and could aid in understanding the evolution of microstructural defect features in fusion relevant conditions.
D-3:IL04 Ab Initio Theory of Solid State Defect Qubits
A. GALI, HUN-REN Wigner Research Centre for Physics & Budapest University of Technology and Economics, Budapest, Hungary
Solid-state defects acting as single photon sources and quantum bits are leading contenders in quantum technologies. Despite great efforts, not all the properties and behaviours of the presently known solid-state defect quantum bits are understood. Furthermore, various quantum technologies require novel solutions, thus new solid-state defect quantum bits should be explored to this end. These issues call to develop ab initio methods which accurately yield the key parameters of solid-state defect quantum bits and vastly accelerate the identification of novel ones for a target quantum technology application. In this paper, we describe recent developments in the field with focusing on the improvement of the accuracy or the predictive power of the methods. We highlight breakthroughs including the description of strong electron-phonon coupling and effective-mass like excited states of deep defects and understanding the leading microscopic effect in the spin-relaxation of isolated nitrogen-vacancy centre in diamond.
D-3:IL05 Theoretical Design Ge/Si Quantum Wells towards Si-based Spin Qubits
JUN-WEI LUO, State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China
In this talk, I will first present our recent theoretical design of Si/Ge heterostructures for large valley splitting towards Si electron spin qubit. I will then report that, contrary to conventional wisdom, we had uncovered a strong and tunable k-linear Rashba SOC in 2DHGs of semiconductor QWs by performing atomistic pseudopotential calculations in conjunction with theoretical analysis based on the effective model Hamiltonian approach. We illustrate that this emergent k-linear Rashba SOC is a first-order direct Rashba effect, originating from a combination of heavy-hole-light-hole mixing and direct dipolar coupling to the external electric field. We then demonstrated that our discovered finite k-linear Rashba SOC of 2D holes offers fast hole-spin control via EDSR with Rabi frequencies in excellent agreement with experimental results over a wide range of driving fields. We also find that the sharp interface is necessary, otherwise random alloy will remarkably suppress this linear Rashba SOC. We further demonstrate a factor of 5 times enhancement on the linear Rashba SOC through engineering the interface potential by varying Si/Ge stacking. These findings bring a deeper understanding of hole-spin qubit manipulation and offer design principles to boost the gate speed.