arXiv subjects

Jianyang Wu

Publications and source records attributed to Jianyang Wu.

14 recordsLinked to original sources

arXiv2025

Stimulating Imagination: Towards General-purpose "Something Something Placement"

General-purpose object placement is a fundamental capability of an intelligent generalist robot: being capable of rearranging objects following precise human instructions even in novel environments. This work is dedicated to achieving general-purpose object placement with ``something something'' instructions. Specifically, we break the entire process down into three parts, including object localization, goal imagination and robot control, and propose a method named SPORT. SPORT leverages a pre-trained large vision model for broad semantic reasoning about objects, and learns a diffusion-based pose estimator to ensure physically-realistic results in 3D space. Only object types (movable or reference) are communicated between these two parts, which brings two benefits. One is that we can fully leverage the powerful ability of open-set object recognition and localization since no specific fine-tuning is needed for the robotic scenario. Moreover, the diffusion-based estimator only need to ``imagine" the object poses after the placement, while no necessity for their semantic information. Thus the training burden is greatly reduced and no massive training is required. The training data for the goal pose estimation is collected in simulation and annotated by using GPT-4. Experimental results demonstrate the effectiveness of our approach. SPORT can not only generate promising 3D goal poses for unseen simulated objects, but also be seamlessly applied to real-world settings.

cs.RO↗

arXiv2023

Accurate prediction of heat conductivity of water by a neuroevolution potential

We propose an approach that can accurately predict the heat conductivity of liquid water. On the one hand, we develop an accurate machine-learned potential based on the neuroevolution-potential approach that can achieve quantum-mechanical accuracy at the cost of empirical force fields. On the other hand, we combine the Green-Kubo method and the spectral decomposition method within the homogeneous nonequilibrium molecular dynamics framework to account for the quantum-statistical effects of high-frequency vibrations. Excellent agreement with experiments under both isobaric and isochoric conditions within a wide range of temperatures is achieved using our approach.

physics.comp-ph↗

arXiv2022

GPUMD: A package for constructing accurate machine-learned potentials and performing highly efficient atomistic simulations

We present our latest advancements of machine-learned potentials (MLPs) based on the neuroevolution potential (NEP) framework introduced in [Fan et al., Phys. Rev. B 104, 104309 (2021)] and their implementation in the open-source package GPUMD. We increase the accuracy of NEP models both by improving the radial functions in the atomic-environment descriptor using a linear combination of Chebyshev basis functions and by extending the angular descriptor with some four-body and five-body contributions as in the atomic cluster expansion approach. We also detail our efficient implementation of the NEP approach in graphics processing units as well as our workflow for the construction of NEP models, and we demonstrate their application in large-scale atomistic simulations. By comparing to state-of-the-art MLPs, we show that the NEP approach not only achieves above-average accuracy but also is far more computationally efficient. These results demonstrate that the GPUMD package is a promising tool for solving challenging problems requiring highly accurate, large-scale atomistic simulations. To enable the construction of MLPs using a minimal training set, we propose an active-learning scheme based on the latent space of a pre-trained NEP model. Finally, we introduce three separate Python packages, GPYUMD, CALORINE, and PYNEP, which enable the integration of GPUMD into Python workflows.

physics.comp-ph↗

arXiv2022

Variable thermal transport in black, blue, and violet phosphorene from extensive atomistic simulations with a neuroevolution potential

Phosphorus has diverse chemical bonds and even in its two-dimensional form there are three stable allotropes: black phosphorene (Black-P), blue phosphorene (Blue-P), and violet phosphorene (Violet-P). Due to the complexity of these structures, no efficient and accurate classical interatomic potential has been developed for them. In this paper, we develop an efficient machine-learned neuroevolution potential model for these allotropes and apply it to study thermal transport in them via extensive molecular dynamics (MD) simulations. Based on the homogeneous nonequilibrium MD method, the thermal conductivities are predicted to be $12.5 \pm 0.2$ (Black-P in armchair direction), $78.4 \pm 0.4$ (Black-P in zigzag direction), $128 \pm 3$ (Blue-P), and $2.36 \pm 0.05$ (Violet-P) $\mathrm{Wm^{-1}K^{-1}}$. The underlying reasons for the significantly different thermal conductivity values in these allotropes are unraveled through spectral decomposition, phonon eigenmodes, and phonon participation ratio. Under external tensile strain, the thermal conductivity in black-P and violet-P are finite, while that in blue-P appears unbounded due to the linearization of the flexural phonon dispersion that increases the phonon mean free paths in the zero-frequency limit.

physics.comp-ph↗

arXiv2022

Abnormally High Thermal Conductivity in Fivefold Twinned Diamond Nanowires

Fivefold twins (5FTs), discovered nearly 200 years ago, are a common multiply twinned structure that usually dramatically deteriorate the thermal transport properties of nanomaterials. Here, we report the anomalous thermal conductivity ($κ$) in a novel fivefold twinned diamond nanowires (5FT-DNWs). The $κ$ of 5FT-DNWs is effectively enhanced by the defects of 5FT boundaries, and non-monotonically changes with the cross-sectional area ($\textit{S}$). Above the critical $\textit{S}$ = 7.1 nm$^{2}$, 5FT-DNWs show a constant value of $κ$, whereas below it, there appears a sharp increase in $κ$ with decreasing $\textit{S}$. More importantly, 5FT-DNWs with minimal $\textit{S}$ show a superior $κ$ over the bulk diamond. By confirming the Normal-process-dominated scattering event, it is demonstrated that the phonon hydrodynamic behavior plays a determinative role in abnormally high $κ$ of 5FT-DNWs with small $\textit{S}$. The super-transported phonon hydrodynamic phenomenon unveiled in the twinned diamond nanowires may provide a new route for pursuing highly thermally conductive nanomaterials.

physics.comp-ph↗

arXiv2021

Strengthening and Weakening by Dislocations in Monolayer MoS2

Dislocations govern the properties of any crystals. Yet, how dislocation of pentagonheptagon (5|7) in grain boundaries (GBs) affects the mechanical properties of two-dimensional MoS2 crystals remains poorly known. Using atomistic simulations and continuum disclination dipole model, we show that, depending on the tilt angle and 5|7 dislocation arrangement, MoS2 GB strength can be enhanced or reduced with tilt angle. For zigzag-tilt GBs primarily composed of Mo5|7+S5|7 dislocations, GB strength monotonically increases as the square of tilt angle. For armchair-tilt GBs with Mo5|7 or S5|7 dislocations, however, the trend of GB strength breaks down as 5|7 dislocations are non-evenly spaced. Moreover, mechanical failure initiates at the bond shared by 5|7 rings, in contrast to graphene where failure occurs at the bond shared by 6|7 rings. This work provides new insights into mechanical design of synthetic transition metal dichalcogenide crystals via dislocation engineering.

cond-mat.mtrl-sci↗

arXiv2021

Mechanical Ductile Detwinning in CH3NH3PbI3 Perovskite

Twin boundaries (TBs) were identified to show conflicting positive/negative effects on the physical properties of CH3NH3PbI3 perovskite, but their roles on the mechanical properties are pending. Herein, tensile characteristics of a variety of TB-dominated bicrystalline CH3NH3PbI3 perovskites are explored using molecular simulations. TB-contained CH3NH3PbI3 are classified into four types from their tensile ductile detwinning characteristics. Type I is characterized by smooth loading flow stressstrain responses, originating from relatively uniform stress distribution induced gradual amorphization at TB region. Types II and III are represented by sudden drop of loading stresses but then distinct ductile flow stress-strain curves, resulting from limited and large-area amorphizations of TB-involved structures, respectively. However, Type IV is highlighted by double apparent peaks in the loading curve followed by ductile flow response, coming from stress-concentration of localization-to-globalization at TB structure, as well as amorphization. This study provides critical insights into mechanics of CH3NH3PbI3 perovskites, and offers that TB engineering is a promising strategy to design mechanically robust hybrid organic-inorganic perovskites-based device systems

cond-mat.mtrl-sci↗

arXiv2021

Effect of Interfacial Dipole on Heterogeneous Ice Nucleation

In this letter, we performed molecular dynamics simulations of ice nucleation on a rigid surface model of cubic zinc blende structure with different surface dipole strength and orientation. It follows that, despite the excellent lattice match between cubic ice and substrates, the ice nucleation happened only when the interfacial water molecules (IWs) have the same or similar orientations as that of the water molecules in cubic ice. The free energy landscapes revealed that, for substrates with improper dipole strength/orientation, large free energy barriers arose to prevent the dipole of IWs rotating to the right orientation to trigger ice formation. Our results suggest that the traditional concept of lattice match, the similarity of lattice length between a substrate and the new-formed crystalline, should be extended to a broader match include the similarity between the molecular orientations of the interfacial component and the component in the specific new-formed crystalline face.

cond-mat.mtrl-sci↗

arXiv2021

Self-assembled Behaviors of Desulphurized $MoS_2$ Monolayer Sheets

Self-assembled topological structures of post-processed two-dimensional materials exhibit novel physical properties distinct from those of their parent materials. Herein, the critical role of desulphurization on self-assembled topological morphologies of molybdenum disulfide ($MoS_2$) monolayer sheets is explored using molecular dynamics (MD) simulations. MD results show that there are differences in atomic energetics of $MoS_2$ monolayer sheets with different desulphurization contents. Both free-standing and substrate-hosted $MoS_2$ monolayer sheets show diversity in topological structures such as flat surface, wrinkles, folds and scrolls, depending on the desulphurization contents, planar dimensions and ratios of length-to-width of $MoS_2$ monolayer sheets. Particularly, at the critical desulphurization contents, they roll up into nanotube morphology, consistent with previous experimental observations. Moreover, the observed differences in the molecular morphological diagrams between free-standing and substrate-hosted $MoS_2$ monolayer sheets can be attributed to unique interatomic interactions and van der Waals interactions in them. The study provides important insights into functionalizing structural morphological properties of two-dimensional materials, e.g., $MoS_2$, via defect engineering.

cond-mat.mtrl-sci↗

arXiv2020

Mechanical Creep Instability of Nanocrystalline Methane Hydrates

Mechanical creep behaviors of natural gas hydrates (NGHs) are of importance for understanding mechanical instability of gas hydrate-bearing sediments on Earth. Limited by the experimental challenges, intrinsic creep mechanisms of nanocrystalline methane hydrates remain largely unknown yet at molecular scale. Herein, using large-scale molecular dynamics (MD) simulations, mechanical creep behaviors of nanocrystalline methane hydrates are investigated. It is revealed that mechanical creep responses are greatly dictated by internal microstructures of crystalline grain size and external conditions of temperature and static stress. Interestingly, a long steady-state creep is observed in nanocrystalline methane hydrates, which can be described by a modified constitutive Bird-Dorn-Mukherjee model. Microstructural analysis show that deformations of crystalline grains, grain boundary (GB) diffusion and GB sliding collectively govern the mechanical creep behaviors of nanocrystalline methane hydrates. Furthermore, structural transformation also appears important in their mechanical creep mechanisms. This study sheds new insights into understanding the mechanical creep scenarios of gas hydrates.

cond-mat.mes-hall↗

arXiv2020

Classical nucleation theory of ice nucleation: second-order correction of thermodynamic parameters

Accurate estimate of nucleation rate is crucial for the study of ice nucleation and ice-promoting/anti-freeze strategies. Within the framework of Classical Nucleation Theory (CNT), the estimate of ice nucleation rate is very sensitive to thermodynamic parameters, such as chemical potential difference between water and ice $Δμ$ and ice-water interfacial free energy $γ$. However, even today, there are still many contradictions and approximations in the estimating of these thermodynamic parameters, introducing large uncertainty to the estimate of the ice nucleation rate. Herein, starting from the basic concepts, for a general solid-liquid crystallization system, we expand the Gibbs-Thomson (GT) equation to second order, and derive the second-order analytical formulas of $Δμ$, $γ$ and nucleation barrier $ΔG$ with combining molecular dynamics (MD) simulations. These formulas describe well the temperature dependence of these thermodynamic parameters. Our results can provide a method of estimating $Δμ$, $γ$ and $ΔG$.

cond-mat.soft↗

arXiv2020

Mechanical Metastructures of Triple Periodic Carbon Clathrates

Clathrates are lightweight, cage-like, fully-sp3 three dimensional (3D) structures that are experimentally-available for several host elements of the IV group. However, carbon clathrates are as yet hypothetical structures. Herein, the mechanical properties of Type-I-C46 Type-II-C34 and Type-H-C34 carbon clathrates are explored by first-principles calculations. It is revealed that those carbon clathrates show distinct anisotropic patterns in ideal tensile/shear strengths and critical tensile/shear strains, with maximum ideal tensile strength of Type-I carbon clathrate that is superior over that of diamond in <111> direction. However, it is identified isotropy in shear Youngs modulus, and in terms of tensile/shear Youngs moduli, they are sorted as Type-I > Type-II > Type-H carbon clathrates. There are distinct critical load-bearing bond configurations that explain their distinct mechanical behaviors. Moreover, those carbon clathrates are intrinsically indirect semiconductors, and their electronic properties can be greatly dictated by mechanical strain. Carbon clathrates can be potentially utilized as lightweight technically robust engineering metastructures and in electromechanical devices.

cond-mat.mtrl-sci↗

arXiv2020

The Effect of Dipole from $γ$-AgI Substrates on Heterogeneous Ice Nucleation

Heterogeneous ice nucleation is one of the most common and important process in the physical environment. AgI has been proved to be an effective ice nucleating agent in the process of ice nucleation. However, the microscopic mechanism of AgI in heterogeneous ice nucleation has not been fully understood. Molecular dynamics simulations are applied to investigate the ability of which kinds of $γ$-AgI substrate can promote ice nucleation by changing the dipole of $γ$-AgI on the substrate, we conclude that the dipole of $γ$-AgI on the substrate can affect the conformation of ice nucleation. The surface ions with positive charge on the substrate may promote ice nucleation, while there is no ice nucleation founded on the surface ions with negative charge. $γ$-AgI substrates affect ice nucleation through adjust the orientations of water molecules near the surfaces.

cond-mat.mtrl-sci↗

arXiv2020

Oxygen Functionalization-induced Crossover in the Tensile Properties of thinnest 2D Ti2C MXene

Transition metal carbides/nitrides (MXenes) are a newly developing class of two-dimensional (2D) materials with technically robust properties that can be finely tuned by planar surface functionalization. Herein, the critical role of oxygen (O-) functionalization on the tensile mechanical characteristics of thinnest 2D Ti2C MXene is explored by molecular dynamic (MD) simulation with first-principle based ReaxFF forcefield. It is demonstrated that Ti2C sheet shows unique tensile mechanical behaviors that pronouncedly vary with the content of O-functionalization and stretching direction. Upon both loading directions, there is an apparent crossover in the Young's modulus, failure strength and failure strain. Intriguingly, under armchair directional load, a structural transition of 1T to 1T' phase occurs in the Ti2C region, which has been observed in many transition metal dichalcogenides. Upon zigzag directional straining, however, two distinct structural transformations take place in pristine and fully O-functionalized Ti2C sheets, respectively. As the load is removed, those three structural transformations are reversible, and they are critically understood by analysis of the bond configurations. The study provides important insights into mechanical behaviors and structural transformations of functionalized MXenes.

cond-mat.mtrl-sci↗