Theoretical evidence of H-He demixing under Jupiter and Saturn conditions.

The immiscibility of hydrogen-helium mixture under the temperature and pressure conditions of planetary interiors is crucial for understanding the structures of gas giant planets (e.g., Jupiter and Saturn).

Discovery of novel materials through machine learning.

Experimental exploration of new materials relies heavily on a laborious trial-and-error approach. In addition to substantial time and resource requirements, traditional experiments and computational modelling are typically limited in finding target materials within the enormous chemical space. Therefore, creating innovative techniques to expedite material discovery becomes essential.

Prediction of Room-Temperature Superconductivity in Quasi-Atomic H-Type Hydrides at High Pressure.

Achieving superconductivity at room temperature (RT) is a holy grail in physics. Recent discoveries on high-T superconductivity in binary hydrides HS and LaH at high pressure have directed the search for RT superconductors to compress hydrides with conventional electron-phonon mechanisms. Here, an exceptional family of superhydrides is predicated under high pressures, MH (M = Mg, Sc, Zr, Hf, Lu), all exhibiting RT superconductivity with calculated Ts ranging from 313 to 398 K.

Phase Transition in Silicon from Machine Learning Informed Metadynamics.

Investigating reconstructive phase transitions in large-sized systems requires a highly efficient computational framework with computational cost proportional to the system size. Traditionally, widely used frameworks such as density functional theory (DFT) have been prohibitively expensive for extensive simulations on large systems that require long-time scales. To address this challenge, this study employed well-trained machine learning potential to simulate phase transitions in a large-size system.

Stability and Semiconducting Behavior of Magnesium Polysulfides by Nonequivalent sp Hybridizations.

The Mg/S battery has attracted enormous interest in recent years due to its high theoretical capacity, low cost, and high security. However, the understanding of many intermediate magnesium polysulfides in the Mg/S battery remains elusive. Combining extensive structural search and first-principles calculations, we investigate the phase stability, structural character, and electronic structure of magnesium polysulfides in a wide range from MgS to MgS.

Self-Limiting Sub-5 nm Nanodiamonds by Geochemistry-Inspired Synthesis.

Controlling diamond structures with nanometer precision is fundamentally challenging owing to their extreme and far-from-equilibrium synthetic conditions. State-of-the-art techniques, including detonation, chemical vapor deposition, mechanical grinding, and high-pressure-high-temperature synthesis, yield nanodiamond particles with a broad distribution of sizes. Despite many efforts, the direct synthesis of nanodiamonds with precisely controlled diameters remains elusive.

Quantum structural fluxion in superconducting lanthanum polyhydride.

The discovery of 250-kelvin superconducting lanthanum polyhydride under high pressure marked a significant advance toward the realization of a room-temperature superconductor. X-ray diffraction (XRD) studies reveal a nonstoichiometric LaH or LaH polyhydride responsible for the superconductivity, which in the literature is commonly treated as LaH without accounting for stoichiometric defects. Here, we discover significant nuclear quantum effects (NQE) in this polyhydride, and demonstrate that a minor amount of stoichiometric defects will cause quantum proton diffusion in the otherwise rigid lanthanum lattice in the ground state.

Size-Dependent Nucleation in Crystal Phase Transition from Machine Learning Metadynamics.

In this Letter, we present a framework that combines machine learning potential (MLP) and metadynamics to investigate solid-solid phase transition. Based on the spectral descriptors and neural networks regression, we develop a scalable MLP model to warrant an accurate interpolation of the energy surface where two phases coexist. Applying it to the simulation of B4-B1 phase transition of GaN under 50 GPa with different model sizes, we observe sequential change of the phase transition mechanism from collective modes to nucleation and growths.

Theoretical methods for structural phase transitions in elemental solids at extreme conditions: statics and dynamics.

In recent years, theoretical studies have moved from a traditionally supporting role to a more proactive role in the research of phase transitions at high pressures. In many cases, theoretical prediction leads the experimental exploration. This is largely owing to the rapid progress of computer power and theoretical methods, particularly the structure prediction methods tailored for high-pressure applications.

Design Principles for High-Temperature Superconductors with a Hydrogen-Based Alloy Backbone at Moderate Pressure.

Hydrogen-based superconductors provide a route to the long-sought goal of room-temperature superconductivity, but the high pressures required to metallize these materials limit their immediate application. For example, carbonaceous sulfur hydride, the first room-temperature superconductor made in a laboratory, can reach a critical temperature (T_{c}) of 288 K only at the extreme pressure of 267 GPa. The next recognized challenge is the realization of room-temperature superconductivity at significantly lower pressures.

Potassium-activated anionic copper and covalent Cu-Cu bonding in compressed K-Cu compounds.

Elemental copper and potassium are immiscible under ambient conditions. It is known that pressure is a useful tool to promote the reaction between two different elements by modifying their electronic structure significantly. Here, we predict the formation of four K-Cu compounds (KCu, KCu, KCu, and KCu) under moderate pressure through unbiased structure search and first-principles calculations.

Quantum and Classical Proton Diffusion in Superconducting Clathrate Hydrides.

The discovery of near room temperature superconductivity in clathrate hydrides has ignited the search for both higher temperature superconductors and deeper understanding of the underlying physical phenomena. In a conventional electron-phonon mediated picture for the superconductivity for these materials, the high critical temperatures predicted and observed can be ascribed to the low mass of the protons, but this also poses nontrivial questions associated with how the proton dynamics affect the superconductivity. Using clathrate superhydride Li_{2}MgH_{16} as an example, we show through ab initio path integral simulations that proton diffusion in this system is remarkably high, with a diffusion coefficient, for example, reaching 6×10^{-6}  cm^{2}/s at 300 K and 250 GPa.

IrN and IrN as potential high-energy-density materials.

Transition metal nitrides have attracted great interest due to their unique crystal structures and applications. Here, we predict two N-rich iridium nitrides (IrN and IrN) under moderate pressure through first-principles swarm-intelligence structural searches. The two new compounds are composed of stable IrN octahedrons and interlinked with high energy polynitrogens (planar N or cyclo-N).

Hydrogen Pentagraphenelike Structure Stabilized by Hafnium: A High-Temperature Conventional Superconductor.

The recent discovery of H_{3}S and LaH_{10} superconductors with record high superconducting transition temperatures T_{c} at high pressure has fueled the search for room-temperature superconductivity in the compressed superhydrides. Here we introduce a new class of high T_{c} hydrides with a novel structure and unusual properties. We predict the existence of an unprecedented hexagonal HfH_{10}, with remarkably high value of T_{c} (around 213-234 K) at 250 GPa.

Nitrogen in black phosphorus structure.

Group V elements in crystal structure isostructural to black phosphorus with unique puckered two-dimensional layers exhibit exciting physical and chemical phenomena. However, as the first element of group V, nitrogen has never been found in the black phosphorus structure. Here, we report the synthesis of the black phosphorus-structured nitrogen at 146 GPa and 2200 K.

o-C: a new sp-dominated allotrope of carbon.

We report a new allotrope of carbon predicted from first principles simulations. This allotrope is formed in a simulated conversion of two-dimensional polymeric Cprecursor subjected to uniaxial compression at high temperature. The structure is made up of 240 carbon atoms in an orthorhombic unit cell (termed as o-C) having a mixed sp/sphybridization with the ratio of about 1:5.

Formation of Stable Compounds of Potassium and Iron under Pressure.

We predict stable stoichiometric potassium-iron (K-Fe) intermetallic compounds at high pressures from first principles. Thermodynamic stability, crystal structures, and bonding properties of these compounds are also investigated. The dynamic stability of the predicted structures is established through phonon calculations while mechanical stability is established through Born-Huang stability criteria.

Pressure-induced structural transformations and new polymorphs in BiVO.

BiVO4 has attracted much attention in recent years due to its active photocatalytic and microwave dielectric properties. BiVO4 exhibits a rich structural polymorphism, and its properties strongly depend on the crystalline phase. Therefore, it is of great importance to achieve an easy control of its crystalline phase.

Superconducting Zirconium Polyhydrides at Moderate Pressures.

Highly compressed hydrides have been at the forefront of the search for high- superconductivity. The recent discovery of record-high 's in HS and LaH under high pressure fuels the enthusiasm for finding good superconductors in similar hydride groups. Guided by first-principles structure prediction, we successfully synthesized ZrH and ZrH at modest pressures (30-50 GPa) in diamond anvil cells by two different reaction routes: ZrH + H at room temperature and Zr + H at ∼1500 K by laser heating.

Mechanism for the Structural Transformation to the Modulated Superconducting Phase of Compressed Hydrogen Sulfide.

A comprehensive description of crystal and electronic structures, structural transformations, and pressure-dependent superconducting temperature (T) of hydrogen sulfide (HS) compressed from low pressure is presented through the analysis of the results from metadynamics simulations. It is shown that local minimum metastable crystal structures obtained are dependent on the choice of pressure-temperature thermodynamic paths. The origin of the recently proposed 'high-T' superconducting phase with a modulated structure and a diffraction pattern reproducing two independent experiments was the low pressure Pmc2 structure.

High-temperature shape memory loss in nitinol: a first principles study.

We have performed first-principles calculations to investigate the possibility of shape memory loss in a member of the binary smart alloy family - NiTi. A detailed analysis of the transition kinetics and dynamical pathway reveals the possibility of the B19' phase of NiTi losing its shape memory when subjected to high stress conditions and is heated above a critical temperature, Tc. The B19' phase is predicted to transform to P1[combining macron]-NiTi, which is also predicted to be dynamically stable and temperature-quench recoverable.

Crystal structures of transition metal pernitrides predicted from first principles.

We have extensively explored the stable crystal structures of early-transition metal pernitrides (TMN, TM = Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, and Ta) at ambient and high pressures using effective CALYPSO global structure search algorithm in combination with first-principles calculations. We identified for the first time the ground-state structures of MnN, TaN, NbN, VN, ZrN, and HfN pernitrides, and proposed their synthesis pressures. All predicted crystal structures contain encapsulated N dumbbells in which the two N atoms are singly bonded to a [N] pernitride unit utilizing the electrons transferred from the transition metals.

Synthesis of Xenon and Iron-Nickel Intermetallic Compounds at Earth's Core Thermodynamic Conditions.

Using in situ synchrotron x-ray diffraction and Raman spectroscopy in concert with first principles calculations we demonstrate the synthesis of stable Xe(Fe,Fe/Ni)_{3} and XeNi_{3} compounds at thermodynamic conditions representative of Earth's core. Surprisingly, in the case of both the Xe-Fe and Xe-Ni systems Fe and Ni become highly electronegative and can act as oxidants. The results indicate the changing chemical properties of elements under extreme conditions by documenting that electropositive at ambient pressure elements could gain electrons and form anions.

B1-B2 phase transition mechanism and pathway of PbS under pressure.

Experimental studies at finite Pressure-Temperature (P-T) conditions and a theoretical study at 0 K of the phase transition in lead sulphide (PbS) have been inconclusive. Many studies that have been done to understand structural transformation in PbS can broadly be classified into two main ideological streams-one with Pnma and another with Cmcm orthorhombic intermediate phase. To foster better understanding of this phenomenon, we present the result of the first-principles study of phase transition in PbS at finite temperature.

Superconducting Hydrogen Sulfide.

The recent discovery of superconductivity above 200 K in hydrogen sulfide under high pressure marks a milestone in superconductor research. Not only does its critical temperature T exceed the previous record in cuprates by more than 50 K, the superconductivity in hydrogen sulfide also exhibits convincing evidence that it is of conventional phonon-mediated type. Moreover, this is the first time that a previously unknown high-T superconductor is predicted by theory and afterwards verified by experiment.