arXiv subjects

Maosheng Miao

Publications and source records attributed to Maosheng Miao.

14 recordsLinked to original sources

arXiv2026

Metal hydrides achieve high-Tc superconductivity at low pressure by mimicking high-pressure H3S chemical bonding

Compressed hydrides are promising candidates for high-temperature superconductivity, yet achieving simultaneous structural stability and high-Tc at low pressures remains challenging. Here, we introduce a new mechanism for accomplishing this goal by mimicking the bonding characteristics of high-pressure H3S within metal hydrides. Using Li3CuH4 as an example, its Cu-H covalent interaction effectively mimics the core function of the S-H bonding in H3S. This interaction not only induces a high hydrogen-derived electronic density of states at the Fermi level, but also softens the hydrogen phonon modes, thereby significantly enhancing the electron-phonon coupling. Furthermore, embedding the strongly ionic Li3H lattice into the covalent Cu-H framework stabilizes the structure at significantly low pressures via a chemical-template effect, while maintaining high-Tc. Li3CuH4 exhibits excellent thermodynamic stability at 20 GPa, with a Tc of 39.25 K at 12 GPa. Further comprehensive high-throughput studies on Li3MH4 (M = transition metal) compounds uncover general principles applicable to a broader range of compounds. This work establishes a new paradigm for the simultaneous optimization of the stability and high-temperature superconductivity of metal hydrides through complementary sublattice interactions, thus advancing the search for practical and viable superconducting materials.

cond-mat.supr-con↗

arXiv2025

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↗

arXiv2023

Intercalating Helium into A-site Vacant Perovskites

Evolutionary searches were employed to predict the most stable structures of perovskites with helium atoms on their A-sites up to pressures of 10 GPa. The thermodynamics associated with helium intercalation into [CaZr]F6, structure that [He]2[CaZr]F6 adopts under pressure, and the mechanical properties of the parent perovskite and helium-bearing phase were studied via density functional theory (DFT) calculations. The pressure-temperature conditions where the formation of HeAlF3, HeGaF3, HeInF3, HeScF3 and HeReO3 from elemental helium and the vacant A-site perovskites is favored were found. Our DFT calculations show that entropy can stabilize the helium-filled perovskites provided that the volume that the noble gas atom occupies within their pores is larger than within the elemental solid at that pressure. We find that helium incorporation will increase the bulk modulus of AlF3 from a value characteristic of tin to one characteristic of steel, and hinders rotations of its octahedra that occur under pressure.

cond-mat.mtrl-sci↗

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↗

arXiv2019

Reverse chemistry of iron in the deep Earth

In this work, we demonstrate a remarkable change of chemical trend of Iron under high pressure that is of great importance for understanding the distribution of elements in the Earth's mantle and core. Using first principles crystal structure search method, we conduct a systematic study of the propensity of p block elements to chemically bind with iron under high pressures ranging from ambient conditions to that of Earth's core. We show that under increasing pressure, iron tends to reverse its chemical nature, changing from an electron donor (reductant) to an electron acceptor, and oxidizes p-block elements in many compounds. Such reverse chemistry has a significant impact on the stoichiometries, bond types and strengths, structures and properties of iron compounds under deep planetary conditions.

physics.chem-ph↗

arXiv2019

High-pressure hybrid materials that can store hydrogen in table salt

We demonstrate in this paper that high pressure can promote the reactions between the ionic compounds and H2 molecules and form thermodynamically stable hybrid compounds. Using crystal structure search method based on first principles calculations and particle swarm optimization algorithm, we show that many alkali halides XY (X=Na, K, Rb, Cs; Y=Cl, Br, I) can form stable hybrid compounds with various H2 compositions under different pressures that could be as low as 0.8 GPa (KIH2). Especially, the commonly known table salt, NaCl, can form stable NaClH2 and NaCl(H2)4 hybrid compounds under pressures of 19.7 and 37.9 GPa, respectively. Our results demonstrate that pressure can promote the formation of solid-molecule hybrid compounds, which reveals a new unique way of discovering novel materials that can combine the advantages of inorganic compounds and small molecules. A direct application of our work is the proof of turning the common table salt and other similar ionic compounds into hydrogen storage materials under moderate pressures.

cond-mat.mtrl-sci↗

arXiv2015

ATLAS: A Real-Space Finite-Difference Implementation of Orbital-Free Density Functional Theory

Orbital-free density functional theory (OF-DFT) is a promising method for large-scale quantum mechanics simulation as it provides a good balance of accuracy and computational cost. Its applicability to large-scale simulations has been aided by progress in constructing kinetic energy functionals and local pseudopotentials. However, the widespread adoption of OF-DFT requires further improvement in its efficiency and robustly implemented software. Here we develop a real-space finite-difference method for the numerical solution of OF-DFT in periodic systems. Instead of the traditional self-consistent method, a powerful scheme for energy minimization is introduced to solve the Euler--Lagrange equation. Our approach engages both the real-space finite-difference method and a direct energy-minimization scheme for the OF-DFT calculations. The method is coded into the ATLAS software package and benchmarked using periodic systems of solid Mg, Al, and Al$_{3}$Mg. The test results show that our implementation can achieve high accuracy, efficiency, and numerical stability for large-scale simulations.

physics.comp-ph↗

arXiv2015

Constructing optimal local pseudopotentials from first principles

Local pseudopotential (LPP) is an important component of the orbital free density functional theory (OF-DFT), which is a promising large scale simulation method that can still maintain information of electron state in materials. Up to date, LPP is usually extracted from the solid state DFT calculations. It is unclear how to assess its transferability while applying to a much different chemical environment. Here we reveal a fundamental relation between the first principles norm-conserving PP (NCPP) and the LPP. Using the optimized effective potential method developed for exchange functional, we demonstrate that the LPP can be constructed optimally from the NCPP for a large number of elements. Our theory also reveals that the existence of an LPP is intrinsic to the elements, irrespective to the parameters used for the construction. Our method provides a unified method in constructing and assessing LPP in the framework of first principles pseudopotentials.

cond-mat.mtrl-sci↗

arXiv2014

Half metallic and insulating phases in BN/Graphene lateral heterostructures

We investigate theoretically the electronic structure of graphene and boron nitride (BN) lateral heterostructures, which were fabricated in recent experiments. The first-principles density functional calculation demonstrates that a huge intrinsic transverse electric field can be induced in the graphene nanoribbon region, and depends sensitively on the edge configuration of the lateral heterostructure. The polarized electric field originates from the charge mismatch at the BN-graphene interfaces. This huge electric field can open a significant bang gap in graphene nanoribbon, and lead to fully spinpolarized edge states and induce half-metallic phase in the lateral BN/Graphene/BN heterostructure with proper edge configurations.

cond-mat.mes-hall↗

arXiv2013

First-principles study of band alignments in the p-type hosts BaM2X2 (M = Cu, Ag; X = S, Se)

The electronic structures of four semiconductor compounds BaCu2S2, BaCu2Se2, BaAg2S2, and BaAg2Se2 are studied by density functional theory using both semi-local and hybrid functionals. The ionization energies and electron affinities were determined by aligning the electronic states with the vacuum level by calculating the electrostatic profile within a supercell slab model. The ionization energy and electron affinity of the compounds were calculated using the Heyd-Scuseria-Ernzerhof (HSE) functionals and range from 4.5 to 5.4 eV and 3.1 to 3.4 eV, respectively. The replacement of Cu by Ag slightly increases the ionization energy and electron affinity, while the replacement of S by Se decreases the ionization energy but slightly increases the electron affinity. Overall, the low ionization energies and small electron affinities suggest that these compounds possess good p-type doping propensities. The band gaps are somewhat small to be ideal candidates for transparent semiconducting behavior. The replacement of Cu with Ag in the barium sulfide compounds can increase the band gap from 1.62 eV to 2.01 eV.

cond-mat.mtrl-sci↗

arXiv2013

Interface-induced Topological Insulator Transition in GaAs/Ge/GaAs Quantum Wells

We demonstrate theoretically that interface engineering can drive Germanium, one of the most commonly-used semiconductors, into topological insulating phase. Utilizing giant electric fields generated by charge accumulation at GaAs/Ge/GaAs opposite semiconductor interfaces and band folding, the new design can reduce the sizable gap in Ge and induce large spin-orbit interaction, which lead to a topological insulator transition. Our work provides a new method on realizing TI in commonly-used semiconductors and suggests a promising approach to integrate it in well developed semiconductor electronic devices.

cond-mat.mes-hall↗

arXiv2012

Diamondoid Structure of Polymeric Nitrogen at High Pressures

High-pressure polymeric structures of nitrogen have attracted great attention owing to their potential application as high-energy-density materials. We report the density functional structural prediction of the unexpected stabilization of a diamondoid (or N10-cage) structure of polymeric nitrogen at high pressures. The structure adopts a highly symmetric body-centered cubic form with lattice sites occupied by N10 tetracyclic cages, each of which consists of 10 atoms and is covalently bonded with its six next-nearest N10 cages. The prediction of this diamondoid structure rules out the earlier proposed helical tunnel phase and demonstrates the high-order nature of polymeric nitrogen at extreme high pressures. Diamondoid nitrogen is a wide-gap insulator and energetically more favorable than the experimental cubic gauche and previously predicted layered Pba2 phases above 263 GPa, a pressure which is accessible to high pressure experiment.

cond-mat.mtrl-sci↗