arXiv subjects

Yuanhui Sun

Publications and source records attributed to Yuanhui Sun.

12 recordsLinked to original sources

arXiv2025

Monolayer Two-dimensional Materials Database (ML2DDB) and Applications

The discovery of two-dimensional (2D) materials with tailored properties is critical to meet the increasing demands of high-performance applications across flexible electronics, optoelectronics, catalysis, and energy storage. However, current 2D material databases are constrained by limited scale and compositional diversity. In this study, we introduce a scalable active learning workflow that integrates deep neural networks with density functional theory (DFT) calculations to efficiently explore a vast set of candidate structures. These structures are generated through physics-informed elemental substitution strategies, enabling broad and systematic discovery of stable 2D materials. Through six iterative screening cycles, we established the creation of the Monolayer 2D Materials Database (ML2DDB), which contains 242,546 DFT-validated stable structures-an order-of-magnitude increase over the largest known 2D materials databases. In particular, the number of ternary and quaternary compounds showed the most significant increase. Combining this database with a generative diffusion model, we demonstrated effective structure generation under specified chemistry and symmetry constraints. This work accomplished an organically interconnected loop of 2D material data expansion and application, which provides a new paradigm for the discovery of new materials.

cond-mat.mtrl-sci↗

arXiv2023

Batch Discovery of New Metal Superhydrides via Chemical Template Theory and Machine Learning

Metal superhydrides, known for their high hydrogen content and polyhedral hydrogen cages, are promising candidates for high-temperature superconductivity. Recent research has emphasized "chemical pre-compression," enabling hydrogen metallization at lower pressures and facilitating the discovery of superconductors with near-room temperature transitions. Despite extensive studies on binary metal superhydrides, there remains a vast, unexplored chemical space, particularly regarding non-integer hydrogen-to-metal ratios. By integrating the "chemical template effect" with machine learning algorithms, we developed a specialized structure discovery workflow that significantly enhances the efficiency of predicting stable superhydrides. Our method led to the identification of 13 new structural prototypes and 31 stable metal superhydrides, representing a 25% increase in discoveries. The 3D hydrogen clathrates in these compounds are strongly correlated with high superconducting transition temperatures, and our approach achieves a remarkable 70% increase. Most of these structures contain over 50 atoms per primitive cell, with the I4/m M10H84 prototype having the largest unit cell, containing 94 atoms. Additionally, 19 of the newly identified superhydrides exhibit superconducting transition temperatures (Tc) exceeding 100 K, highlighting the potential for higher Tc materials within the 3D hydrogen clathrate structures. The method also shows good potential to search for ternary superhydrides on a large scale.

cond-mat.supr-con↗

arXiv2022

Unified chemical theory of structure and bonding in elemental metals

Most elemental metals under ambient conditions adopt simple structures such as BCC, FCC and HCP in specific groupings across the Periodic Table, and on compression, many of these elements undergo transitions to surprisingly complex structures, including open and low-symmetry phases not expected from conventional free-electron based theories of metals. First-principles calculations have been able to reproduce many observed structures and transitions, but a unified, predictive theory of bonding that underlies this behavior is not yet in hand. We propose a remarkably simple theory based on large-scale high-throughput calculations of the elements over a broad range of thermodynamic conditions. The results broaden the conventional concept of metallic bonding with a new perspective that both explains the stability of different simple structures as well as lower symmetry phases arising from electron localization at interstitial sites in these structures. The success of this simple framework reveals the important role of chemical interactions in governing the structures and electronic properties of simple metals.

cond-mat.mtrl-sci↗

arXiv2021

Abnormal behavior of Cs polyoxides under high pressure

High-pressure can transform the structures and compositions of materials either by changing the relative strengths of bonds or by altering the oxidation states of atoms. Both effects cause unconventional compositions in novel compounds that have been synthesized or predicted in large numbers in the past decade. What naturally follows is a question: what if pressure imposes strong effects on both chemical bonds and atomic orbitals in the same material. A systematic DFT and crystal structure search study of Cs polyoxides under high pressure shows a striking transition of chemistry due to the activation of the Cs 5p core electrons. Opposing to the general trend of polyoxides, the O-O bonds disappear in Cs polyoxides and Cs and O atoms form molecules and monolayers with strong Cs-O covalent bonds. Especially, the abnormal transition of structure and chemical bonds happens to CsO, a solid peroxide that is stable under ambient pressure, at 221 GPa, which can be accessed by current high-pressure experiments.

cond-mat.mtrl-sci↗

arXiv2021

Chemical templates that assemble the metal superhydrides

The recent discoveries of many metal superhydrides provide a new route to room-temperature superconductors. However, their stability and structure trends and the large chemical driving force needed to dissociate H2 molecules and form H covalent network cannot be explained by direct metal-hydrogen bonds and volume effect. Here, we demonstrate that the understanding of superhydrides formation needs a perspective beyond traditional chemical bond theory. Using high-throughput calculations, we show that, after removing H atoms, the remaining metal lattices exhibit large electron localization at the interstitial regions, which matches excellently to the H lattice like a template. Furthermore, H lattices consist of 3D aromatic building units that are greatly stabilized by chemical templates of metals close to s-d border. The chemical template theory can naturally explain the stability and structure trends of superhydrides and help to predict new materials such as two-metal superhydrides.

cond-mat.mtrl-sci↗

arXiv2021

JAMIP: an artificial-intelligence aided data-driven infrastructure for computational materials informatics

Materials informatics has emerged as a promisingly new paradigm for accelerating materials discovery and design. It exploits the intelligent power of machine learning methods in massive materials data from experiments or simulations to seek for new materials, functionality, principles, etc. Developing specialized facility to generate, collect, manage, learn and mine large-scale materials data is crucial to materials informatics. We herein developed an artificial-intelligence-aided data-driven infrastructure named Jilin Artificial-intelligence aided Materials-design Integrated Package (JAMIP), which is an open-source Python framework to meet the research requirements of computational materials informatics. It is integrated by materials production factory, high-throughput first-principles calculations engine, automatic tasks submission and monitoring progress, data extraction, management and storage system, and artificial intelligence machine learning based data mining functions. We have integrated specific features such as inorganic crystal structure prototype database to facilitate high-throughput calculations and essential modules associated with machine learning studies of functional materials. We demonstrated how our developed code is useful in exploring materials informatics of optoelectronic semiconductors by taking halide perovskites as typical case. By obeying the principles of automation, extensibility, reliability and intelligence, the JAMIP code is a promisingly powerful tool contributing to the fast-growing field of computational materials informatics.

cond-mat.mtrl-sci↗

arXiv2020

New Polymorphs of Two-Dimensional Indium Selenide with Enhanced Electronic Properties

The two-dimensional (2D) semiconductor indium selenide (InSe) has attracted significant interest due its unique electronic band structure, high electron mobility and wide tunability of its band gap energy achieved by varying the layer thickness. All these features make 2D InSe a potential candidate for advanced electronic and optoelectronic applications. Here, we report on the discovery of new polymorphs of InSe with enhanced electronic properties. Using a global structure search that combines artificial swarm intelligence with first-principles energetic calculations, we identify polymorphs that consist of a centrosymmetric monolayer belonging to the point group D$_{3d}$, distinct from the well-known polymorphs based on the D$_{3h}$ monolayers that lack inversion symmetry. The new polymorphs are thermodynamically and kinetically stable, and exhibit a wider optical spectral response and larger electron mobilities compared to the known polymorphs. We discuss opportunities to synthesize these newly discovered polymorphs and viable routes to identify them by X-ray diffraction, Raman spectroscopy and second harmonic generation experiments.

cond-mat.mtrl-sci↗

arXiv2019

Switchable out-of-plane polarization in two-dimensional LiAlTe$_2$

Covalent-polar semiconductors that show intrinsic two-dimensional (2D) vertical polarization present new device opportunities. These materials differ from ordinary ferroelectrics in that they are able to maintain polarization normal to a surface even with an unscreened depolarization field. Identifying phases that exhibit intrinsic 2D vertical polarization is an ongoing challenge. Here we report via computational material design the discovery of a new promising phase, specifically 2D LiAlTe$_2$. The design idea is developed from the physical understanding of three-dimensional hyperferroelectric covalent polar semiconductors. We used the structure determination method combining swarm intelligence algorithm and first-principles calculations to identify energetically stable structures. In addition to the expected layered version of bulk LiAlTe$_2$, $β$-LiAlTe$_2$, we find a novel 2D structure, $γ$-LiAlTe$_2$. In this phase, the vertical dipole can be switched between 0.07 and -0.11 e$\cdot$angstrom. This switching is triggered by the movement of Li atom between two local energy minima. The associated asymmetric double-well energy profile can be continuously tuned by the applied electric field as well as strain. There is, therefore, a reversible transition between two polar states. This discovered off-plane switchability provides an opportunity for the 2D $γ$-LiAlTe$_2$ based interfacial phase change memory device for example by growing $γ$-LiAlTe$_2$/GeTe heterostructures.

cond-mat.mtrl-sci↗

arXiv2018

Experimental identification of critical condition for drastically enhancing thermoelectric power factor of two-dimensional layered materials

Nano-structuring is an extremely promising path to high performance thermoelectrics. Favorable improvements in thermal conductivity are attainable in many material systems, and theoretical work points to large improvements in electronic properties. However, realization of the electronic benefits in practical materials has been elusive experimentally. A key challenge is that experimental identification of the quantum confinement length, below which the thermoelectric power factor is significantly enhanced, remains elusive due to lack of simultaneous control of size and carrier density. Here we investigate gate tunable and temperature-dependent thermoelectric transport in $γ$ phase indium selenide ($γ$ InSe, n type semiconductor) samples with thickness varying from 7 to 29 nm. This allows us to properly map out dimension and doping space. Combining theoretical and experimental studies, we reveal that the sharper pre-edge of the conduction-band density of states arising from quantum confinement gives rise to an enhancement of the Seebeck coefficient and the power factor in the thinner InSe samples. Most importantly, we experimentally identify the role of the competition between quantum confinement length and thermal de Broglie wavelength in the enhancement of power factor. Our results provide an important and general experimental guideline for optimizing the power factor and improving the thermoelectric performance of two-dimensional layered semiconductors.

cond-mat.mes-hall↗

arXiv2018

Interlayer Coupling in Two-Dimensional Semiconductor Materials

Two-dimensional (2D) graphene-like layered semiconductors provide a new platform for materials research because of their unique mechanical, electronic and optical attributes. Their in-plane covalent bonding and dangling-bond-free surface allow them to assemble various van der Waals heterostructures (vdWHSs) with sharply atomic interfaces that are not limited by lattice matching and material compatibility. Interlayer coupling, as a ubiquitous phenomenon residing among 2D materials (2DMs) systems, controls a thin layer exfoliation process and the assembly of vdWHSs and behaves with a unique degree of freedom for engineering the properties of 2DMs. Interlayer coupling provides an opportunity to observe new physics and provides a novel strategy to modulate the electronic and optoelectronic properties of materials for practical device applications. We herein review recent progress in the exploration of interlayer coupling in 2D semiconducting vdWHSs for potential applications in electronics and optoelectronics.

cond-mat.mtrl-sci↗

arXiv2018

InSe: a two-dimensional material with strong interlayer coupling

Atomically thin, two-dimensional (2D) indium selenide (InSe) has attracted considerable attention due to large tunability in the band gap (from 1.4 to 2.6 eV) and high carrier mobility. The intriguingly high dependence of band gap on layer thickness may lead to novel device applications, although its origin remains poorly understood, and generally attributed to quantum confinement effect. In this work, we demonstrate via first-principles calculations that strong interlayer coupling may be mainly responsible for this phenomenon, especially in the fewer-layer region, and it could also be an essential factor influencing other material properties of β-InSe and γ-InSe. Existence of strong interlayer coupling manifests itself in three aspects: (i) indirect-to-direct band gap transitions with increasing layer thickness; (ii) fan-like frequency diagrams of the shear and breathing modes of few-layer flakes; (iii) strong layer-dependent carrier mobilities. Our results indicate that multiple-layer InSe may be deserving of attention from FET-based technologies and also an ideal system to study interlayer coupling, possibly inherent in other 2D materials.

cond-mat.mtrl-sci↗

arXiv2017

Cu-In Halide Perovskite solar absorbers

The long-term chemical instability and the presence of toxic Pb in otherwise stellar solar absorber APbX$_{3}$ have hindered their large-scale commercialization. Previously explored ways to achieve Pb-free halide perovskites involved replacing Pb$^{2+}$ with other similar M$^{2+}$ cations in ns$^2$ electron configuration, e.g., Sn$^{2+}$ or by Bi$^{3+}$ (plus Ag$^+$), but unfortunately this showed either poor stability (M = Sn) or weakly absorbing oversized indirect gaps (M = Bi), prompting concerns that perhaps stability and good optoelectronic properties might be contraindicated. Herein, we exploit the electronic structure underpinning of classic Cu[In,Ga]Se$_{2}$ (CIGS) chalcopyrite solar absorbers to design Pb-free halide perovskites by transmuting 2Pb to the pair [B$^{IB}$ + C$^{III}$]. The resulting group of double perovskites with formula A$_2$BCX$_6$ (A = K, Rb, Cs; B = Cu, Ag; C = Ga, In; X = Cl, Br, I) benefits from the ionic, yet narrow-gap character of halide perovskites, and at the same time borrows the advantage of the strong and rapidly rising Cu(d)/Se(p) $\rightarrow$ Ga/In(s/p) valence-to-conduction-band absorption spectra known from CIGS. This constitutes a new group of CuIn-based Halide Perovskite (CIHP). Our first-principles calculations guided by such design principles indicate that the CIHPs class has members with clear thermodynamic stability, showing rather strong direct-gap optical transitions, and manifesting a wide-range of tunable gap values (from zero to about 2.5 eV) and combination of light electron and heavy-light hole effective masses. Materials screening of candidate CHIPs then identifies the best-of-class Rb$_2$[CuIn]Cl$_6$, Rb$_2$[AgIn]Br$_6$ and Cs$_2$[AgIn]Br$_6$, having direct band gaps of 1.36, 1.46 and 1.50 eV, and a theoretical spectroscopic limited maximal efficiency comparable to chalcopyrites and CH$_3$NH$_3$PbI$_3$.

cond-mat.mtrl-sci↗