arXiv subjects

Lin-Wang Wang

Publications and source records attributed to Lin-Wang Wang.

At least 19 recordsLinked to original sources

arXiv2026

Trillion-atom molecular dynamics simulations with ab initio accuracy

Material properties are fundamentally dictated by multiscale phenomena, which often reach mesoscale in size. The {\mu}m mesoscale is also the size which can be observed directly under an optical microscope, bridging the atomistic microscopic description with the continuous model macroscopic world. In this work, we report an unprecedented molecular dynamics (MD) simulation comprising 1.62 trillion atoms. Utilizing the neuroevolution potential (NEP) framework, we attained ab initio accuracy on China's New-generation Intelligent Supercomputer. Our implementation achieves a time-to-solution (s/step/atom) 100 times faster than previous state-of-the-art machine learning force field simulations, and 1,000 times faster than the Gordon Bell Prize-winning application from six years ago. Furthermore, we demonstrate an 86.9% weak scaling efficiency from a single GPGPU to 45,000 GPGPUs. These results redefine atomistic simulation boundaries, enabling direct mesoscopic modeling with quantum-level precision.

cond-mat.mtrl-sci↗

arXiv2026

A Route to Nonrelativistic Altermagnetic Spin Splitting via Ultrafast Light

We identify a nonequilibrium route for generating altermagnetic spin splitting in antiferromagnet by ultrafast light. Unlike existing strategies, this route does not require relativistic angular-momentum transfer, static symmetry breaking, or auxiliary external fields. Using real-time time-dependent density functional theory, we demonstrate in the antiferromagnetic perovskite KNiF3 that linearly polarized light can induce momentum-dependent altermagnetic spin splitting by breaking the effective time-reversal symmetry through photoexcited charge redistribution and the resulting lattice distortion. We provide a general symmetry selection rule for this route. These results establish a mechanism for ultrafast control of altermagnetism and extend its material realization into the nonequilibrium regime.

cond-mat.mtrl-sci↗

arXiv2025

Enhancing Cutoff Energy of Solid High-Harmonic Generation from Bonding Length Perspective

High-harmonic generation (HHG) from solid state offers promising potential for attosecond optics with enhanced efficiency and compact configurations. However, Current implementations face critical limitations imposed by material damage thresholds, directly restricting spectral cutoff energies in nonperturbative regime. In this study, we control the cutoff energy through tailoring the bond length of materials, which is available by experimental strain. Employing real-time time-dependent density theory (rt-TDDFT) simulations, we find that the cutoff energy increases by nearly one third under a bond length compression of 7.5%. Our results reveal that it originates the band gap widening inducing the enhancement of interband cutoff energy, which is material-independent. This work provides novel theoretical insights for optimizing extreme ultraviolet sources, advancing potential applications in attosecond physics.

physics.optics↗

arXiv2025

Occupation-Driven emission asynchronous as a Fundamental Constraint on Solid-State Attosecond Pulses

A newly analytic occupation-resolved theory capturing the temporal structure of attosecond pulses (APs) is derived. We validate it with real-time time-dependent density functional theory and show remarkable temporal confinement of APs with laser intensity in solid state. Using a simplified field-driven electron excitation together with a generalized pre-acceleration picture, the interband emission timing demonstrate intrinsically temporal mismatched with field-synchronous intraband radiation, leading to a nonmonotonic dependence of attosecond pulse width on laser intensity. Our findings not only shed light on the microscopic mechanisms behind solid-state high harmonic generation (HHG), but also establish the fundamental time-domain constraint on solid-state APs independent of material damage thresholds.

physics.optics↗

arXiv2025

Origin of Suppressed Ferroelectricity in k-Ga$_2$O$_3$: Interplay Between Polarization and Lattice Domain Walls

The large discrepancy between experimental and theoretical remanent polarization and coercive field limits the applications of wide-band-gap ferroelectric materials. Here, using a machine-learning potential trained on ab-initio molecular dynamics data, we identify a new mechanism of the interplay between polarization domain wall (PDW) and lattice domain wall (LDW) in ferroelectric k-phase gallium oxide (Ga2O3), which reconciles predictions with experimental observations. Our results reveal that the reversal of out-of-plane polarization is achieved through in-plane sliding and shear of the Ga-O sublayers. This pathway creates strong anisotropy in PDW propagation, and crucially leads to topologically forbidden PDW propagation across the 120 degree LDWs observed in synthesized samples. The resulting stable network of residual domain walls bypasses slow nucleation and suppresses the observable polarization and coercive field. These insights highlight the potential for tailoring the ferroelectric response in k-Ga2O3 from lattice-domain engineering.

cond-mat.mtrl-sci↗

arXiv2025

Revealing Material-Dependent Bicircular High-Order Harmonic Generation in 2D Semiconductors via Real-Space Trajectories

Solid-state high-order harmonic generation (HHG) presents unique features different from gases.Whereas the gaseous harmonics driven by counter-rotating bicircular (CRB) pulse universally peak at a "magic" field ratio approximately E_2{\omega}:E_{\omega}=1.5:1, crystals exhibit significant material-dependent responses. In monolayer MoS2, the harmonic yield experiences two maxima at the gas-like 1.5:1 ratio, and again in the single-color limit, whereas monolayer hBN shows a monotonic increase as the 2{\omega} component dominates. Combining time-dependent density-functional theory (TDDFT) and a minimal real-space trajectory analysis, we show that these differences arise from the interplay of Bloch velocity and anomalous Hall velocity. The trajectory model quantitatively reproduces the ab-initio results, and offers an intuitive prediction of the harmonics yield without further heavy computation. These insights provide practical guidance for tailoring solid-state HHG and for selecting 2D compounds with desirable responses.

physics.optics↗

arXiv2025

Ultrafast dynamics of atomic correlated disordering in photoinduced VO$_2$

Recent experiments suggest that atomic disordering dynamics are more universal than conventional coherent processes in photoinduced phase transitions (PIPTs), yet its mechanism remains unclear. Using real-time time-dependent density functional theory (rt-TDDFT), we find that, at lower photoexcitation, higher lattice temperature accelerates atomic disordering, which thereby lowers the threshold for phase transition, by thermally exciting more phonons to randomize the lattice vibrations in VO$_2$. Above this threshold, however, we observe that the transition timescale and atomic disordering become temperature-independent since thermally excited lattice vibrations induce a similar evolution of photoexcited holes. Additionally, we show that photoexcitation initially elongates the V-V dimers followed by a rotation with tangential displacements (along the z-axis) mediated by O atoms, resulting in strongly correlated motion along the z-axis. Consequently, atomic disordering is more dominant along the x direction, attributed to the relatively unrestricted motion of V-V dimers along this direction. The motion of V atoms along the z-axis is more constrained, leading to less disorder along the z-axis, which results in a "correlated disorder" phenomenon. This anisotropic disordering in VO$_2$ offers new insights into PIPTs mechanisms, guiding future studies on photoinduced disordered transitions.

cond-mat.mtrl-sci↗

arXiv2025

Raman Forbidden Layer-Breathing Modes in Layered Semiconductor Materials Activated by Phonon and Optical Cavity Effects

We report Raman forbidden layer-breathing modes (LBMs) in layered semiconductor materials (LSMs). The intensity distribution of all observed LBMs depends on layer number, incident light wavelength and refractive index mismatch between LSM and underlying substrate. These results are understood by a Raman scattering theory via the proposed spatial interference model, where the naturally occurring optical and phonon cavities in LSMs enable spatially coherent photon-phonon coupling mediated by the corresponding one-dimensional periodic electronic states. Our work reveals the spatial coherence of photon and phonon fields on the phonon excitation via photon/phonon cavity engineering.

cond-mat.mtrl-sci↗

arXiv2025

Unconventional bias-dependent tunneling magnetoresistance in van der Waals ferromagnetic/semiconductor heterojunctions

Two-dimensional van der Waals (vdW) ferromagnetic/semiconductor heterojunctions represent an ideal platform for studying and exploiting tunneling magnetoresistance (TMR) effects due to the versatile band structure of semiconductors and their high-quality interfaces. In the all-vdW magnetic tunnel junction (MTJ) devices, both the magnitude and sign of the TMR can be tuned by an applied voltage. Typically, as the bias voltage increases, first the amplitude of the TMR decreases, then the sign of the TMR reverses and/or oscillates. Here, we report on an unconventional bias-dependent TMR in the all-vdW Fe3GaTe2/GaSe/Fe3GaTe2 MTJs, where the TMR first increases, then decreases, and finally undergoes a sign reversal as the bias voltage increases. This dependence cannot be explained by traditional models of MTJs. We propose an in-plane electron momentum (k//) resolved tunneling model that considers both the coherent degree of k// and the decay of the electron wave function through the semiconductor spacer layer. This can explain well the conventional and unconventional bias-dependent TMR. Our results thus provide a deeper understanding of the bias-dependent spin-transport in semiconductor-based MTJs and offer new insights into semiconductor spintronics.

cond-mat.mtrl-sci↗

arXiv2024

FastCHGNet: Training one Universal Interatomic Potential to 1.5 Hours with 32 GPUs

Graph neural network universal interatomic potentials (GNN-UIPs) have demonstrated remarkable generalization and transfer capabilities in material discovery and property prediction. These models can accelerate molecular dynamics (MD) simulation by several orders of magnitude while maintaining \textit{ab initio} accuracy, making them a promising new paradigm in material simulations. One notable example is Crystal Hamiltonian Graph Neural Network (CHGNet), pretrained on the energies, forces, stresses, and magnetic moments from the MPtrj dataset, representing a state-of-the-art GNN-UIP model for charge-informed MD simulations. However, training the CHGNet model is time-consuming(8.3 days on one A100 GPU) for three reasons: (i) requiring multi-layer propagation to reach more distant atom information, (ii) requiring second-order derivatives calculation to finish weights updating and (iii) the implementation of reference CHGNet does not fully leverage the computational capabilities. This paper introduces FastCHGNet, an optimized CHGNet, with three contributions: Firstly, we design innovative Force/Stress Readout modules to decompose Force/Stress prediction. Secondly, we adopt massive optimizations such as kernel fusion, redundancy bypass, etc, to exploit GPU computation power sufficiently. Finally, we extend CHGNet to support multiple GPUs and propose a load-balancing technique to enhance GPU utilization. Numerical results show that FastCHGNet reduces memory footprint by a factor of 3.59. The final training time of FastCHGNet can be decreased to \textbf{1.53 hours} on 32 GPUs without sacrificing model accuracy.

cs.DC↗

arXiv2024

ALKPU: an active learning method for the DeePMD model with Kalman filter

Neural network force field models such as DeePMD have enabled highly efficient large-scale molecular dynamics simulations with ab initio accuracy. However, building such models heavily depends on the training data obtained by costly electronic structure calculations, thereby it is crucial to carefully select and label the most representative configurations during model training to improve both extrapolation capability and training efficiency. To address this challenge, based on the Kalman filter theory we propose the Kalman Prediction Uncertainty (KPU) to quantify uncertainty of the model's prediction. With KPU we design the Active Learning by KPU (ALKPU) method, which can efficiently select representative configurations that should be labelled during model training. We prove that ALKPU locally leads to the fastest reduction of model's uncertainty, which reveals its rationality as a general active learning method. We test the ALKPU method using various physical system simulations and demonstrate that it can efficiently coverage the system's configuration space. Our work demonstrates the benefits of ALKPU as a novel active learning method, enhancing training efficiency and reducing computational resource demands.

physics.comp-ph↗

arXiv2024

Realtime observation of a tungsten-promoted size regulation mechanism in a rhodium catalyst at atomic resolution

The static and genuine structure of small rhodium and rhodium/tungsten nanoparticles on an alumina support can be imaged with atomic resolution even if single digit atom clusters are investigated. Low dose rate electron microscopy is key to the achievement and can generally be applied to investigate any similar material. In such conditions it becomes feasible to identify the chemical composition of nanocrystals from quantitative contrast analyses alone by counting atoms. The ability to fully characterize an unaltered, initial state of the objects allows targeting structural excitations or conformational changes induced by the electron beam itself. For the specific case of catalytic Rh:W particles we stimulate a tungsten-promoted size regulation mechanism in real time that is driven by Oswald ripening and can be understood by a strong binding of tungsten atoms to the oxygen atoms of the support, which builds up strain as the cluster sizes increase.

cond-mat.mtrl-sci↗

arXiv2024

The photoinduced hidden metallic phase of monoclinic VO2 driven by local nucleation via a self-amplification process

The insulator-to-metal transition (IMT) in vanadium dioxide (VO2) has garnered extensive attention for its potential applications in ultrafast switches, neuronal network architectures, and storage technologies. However, a significant controversy persists regarding the formation of the IMT, specifically concerning whether a complete structural phase transition from monoclinic (M1) to rutile (R) phase is necessary. Here we employ the real-time time-dependent density functional theory (rt-TDDFT) to track the dynamic evolution of atomic and electronic structures in photoexcited VO2, revealing the emergence of a long-lived monoclinic metal phase (MM) under low electronic excitation. The emergence of the metal phase in the monoclinic structure originates from the dissociation of the local V-V dimer, driven by the self-trapped and self-amplified dynamics of photoexcited holes, rather than by a pure electron-electron correction. On the other hand, the M1-to-R phase transition does appear at higher electronic excitation. Our findings validate the existence of MM phase and provide a comprehensive picture of the IMT in photoexcited VO2.

cond-mat.mtrl-sci↗

arXiv2024

Atomic evolution of hydrogen intercalation wave dynamics in palladium nanocrystals

Solute-intercalation-induced phase separation creates spatial heterogeneities in host materials, a phenomenon ubiquitous in batteries, hydrogen storage, and other energy devices. Despite many efforts, probing intercalation processes at the atomic scale has been a significant challenge. We study hydrogen (de)intercalation in palladium nanocrystals as a model system and achieve atomic-resolution imaging of hydrogen intercalation wave dynamics by utilizing liquid-phase transmission electron microscopy. Our observations reveal that intercalation wave mechanisms, instead of shrinking-core mechanisms, prevail at ambient temperature for palladium nanocubes ranging from ~60 nm down to ~10 nm. We uncover the atomic evolution of hydrogen intercalation wave transitioning from non-planar and inclined boundaries to those closely aligned with {100} planes. Our kinetic Monte Carlo simulations demonstrate the observed intercalation wave dynamics correspond to sorption pathways minimizing the lattice mismatch strain at the phase boundary. Unveiling the atomic intercalation pathways holds profound implications for engineering intercalation-mediated devices and advancements in energy sciences.

cond-mat.stat-mech↗

arXiv2023

Observation of spin-momentum locked surface states in amorphous Bi$_{2}$Se$_{3}$

Crystalline symmetries have played a central role in the identification of topological materials. The use of symmetry indicators and band representations have enabled a classification scheme for crystalline topological materials, leading to large scale topological materials discovery. In this work we address whether amorphous topological materials, which lie beyond this classification due to the lack of long-range structural order, exist in the solid state. We study amorphous Bi$_2$Se$_3$ thin films, which show a metallic behavior and an increased bulk resistance. The observed low field magnetoresistance due to weak antilocalization demonstrates a significant number of two dimensional surface conduction channels. Our angle-resolved photoemission spectroscopy data is consistent with a dispersive two-dimensional surface state that crosses the bulk gap. Spin resolved photoemission spectroscopy shows this state has an anti-symmetric spin texture resembling that of the surface state of crystalline Bi$_2$Se$_3$. These experimental results are consistent with theoretical photoemission spectra obtained with an amorphous tight-binding model that utilizes a realistic amorphous structure. This discovery of amorphous materials with topological properties uncovers an overlooked subset of topological matter outside the current classification scheme, enabling a new route to discover materials that can enhance the development of scalable topological devices.

cond-mat.mtrl-sci↗

arXiv2022

RLEKF: An Optimizer for Deep Potential with Ab Initio Accuracy

It is imperative to accelerate the training of neural network force field such as Deep Potential, which usually requires thousands of images based on first-principles calculation and a couple of days to generate an accurate potential energy surface. To this end, we propose a novel optimizer named reorganized layer extended Kalman filtering (RLEKF), an optimized version of global extended Kalman filtering (GEKF) with a strategy of splitting big and gathering small layers to overcome the $O(N^2)$ computational cost of GEKF. This strategy provides an approximation of the dense weights error covariance matrix with a sparse diagonal block matrix for GEKF. We implement both RLEKF and the baseline Adam in our $α$Dynamics package and numerical experiments are performed on 13 unbiased datasets. Overall, RLEKF converges faster with slightly better accuracy. For example, a test on a typical system, bulk copper, shows that RLEKF converges faster by both the number of training epochs ($\times$11.67) and wall-clock time ($\times$1.19). Besides, we theoretically prove that the updates of weights converge and thus are against the gradient exploding problem. Experimental results verify that RLEKF is not sensitive to the initialization of weights. The RLEKF sheds light on other AI-for-science applications where training a large neural network (with tons of thousands parameters) is a bottleneck.

physics.comp-ph↗

arXiv2022

Origin of Immediate Damping of Coherent Oscillations in Photoinduced Charge Density Wave Transition

In stark contrast to the conventional charge density wave (CDW) materials, the one-dimensional CDW on the In/Si(111) surface exhibits immediate damping of the CDW oscillation during the photoinduced phase transition. Here, by successfully reproducing the experimentally observed photoinduced CDW transition on the In/Si(111) surface by performing real-time time-dependent density functional theory (rt-TDDFT) simulations, we demonstrate that photoexcitation promotes valence electrons from Si substrate to empty surface bands composed primarily of the covalent p-p bonding states of the long In-In bonds, generating interatomic forces to shorten the long bonds and in turn drives coherently the structural transition. We illustrate that after the structural transition, the component of these surface bands occurs a switch among different covalent In bonds, causing a rotation of the interatomic forces by about {\pi}/6 and thus quickly damping the oscillations in feature CDW modes. These findings provide a deeper understanding of photoinduced phase transitions.

cond-mat.mtrl-sci↗

arXiv2022

Strong structural and electronic coupling in metavalent PbS moire superlattices

Moire superlattices are twisted bilayer materials, in which the tunable interlayer quantum confinement offers access to new physics and novel device functionalities. Previously, moire superlattices were built exclusively using materials with weak van der Waals interactions and synthesizing moire superlattices with strong interlayer chemical bonding was considered to be impractical. Here using lead sulfide (PbS) as an example, we report a strategy for synthesizing of moire superlattices coupled by strong chemical bonding. We use water-soluble ligands as a removable template to obtain free-standing ultra-thin PbS nanosheets and assemble them into direct-contact bilayers with various twist angles. Atomic-resolution imaging shows the moire periodic structural reconstruction at superlattice interface, due to the strong metavalent coupling. Electron energy loss spectroscopy and theoretical calculations collectively reveal the twist angle26 dependent electronic structure, especially the emergent separation of flat bands at small twist angles. The localized states of flat bands are similar to well-arranged quantum dots, promising an application in devices. This study opens a new door to the exploration of deep energy modulations within moire superlattices alternative to van der Waals twistronics.

cond-mat.mtrl-sci↗