arXiv subjects

Zepeng Wu

Publications and source records attributed to Zepeng Wu.

8 recordsLinked to original sources

arXiv2026

Assessing foundational atomistic models for iron alloys under Earth's core conditions

We assess the capability of recently developed foundational atomistic models (FAMs) to simulate iron alloys under the extreme pressures and temperatures of Earth's core. Static equations of state for hexagonal close-packed (hcp) and body-centered cubic (bcc) iron, computed using 17 FAMs, are benchmarked against ab initio calculations. Two representative models, MatterSim and MACE, are further evaluated for their ability to reproduce phonon spectra, liquid structure, and melting relations of iron at core conditions. While both models capture several key properties, MACE substantially overestimates the stability of bcc iron and fails to correctly describe the stability of hcp iron. Their performance is also examined for binary liquids, superionic phases, and a seven-component Fe-Ni-Si-S-O-H-C liquid. Although these FAMs were not explicitly trained on data from core conditions, they can reproduce several structural and dynamical properties across a wide range of compositions. However, none of the tested models consistently reproduces all first-principles benchmarks. By analyzing the origins of these discrepancies, we identify several limitations of current FAMs, particularly the lack of an explicit treatment of thermal electronic excitations, which significantly affect phase stability and thermodynamic properties under core conditions. We further discuss directions for improving FAMs to enable predictive simulations of core-forming materials under extreme conditions.

physics.geo-ph↗

arXiv2026

Radial gradient of superionic hydrogen in Earth's inner core

Hydrogen is considered a key light element in Earth's core, yet the thermodynamics of its superionic phase and its distribution in the inner core remain unclear. Here, we compute ab initio Gibbs free energies for liquid and superionic hcp and bcc Fe-H phases and construct the superionic-liquid phase diagram over pressure-temperature conditions relevant to the Earth's inner core. We find that phase diagrams at different inner-core pressures collapse when temperatures are scaled by the melting temperature of pure iron, indicating that solid-liquid partitioning is controlled primarily by a reduced temperature relative to iron melting and is weakly sensitive to pressure. This scaling relation further reconciles previously reported discrepancies in partition coefficients among theoretical studies and yields good agreement with available experimental data at low pressures. By applying thermochemical constraints, our free-energy results reveal a radial hydrogen gradient within the inner core. These results demonstrate that compositional gradients of superionic hydrogen in the inner core emerge naturally from equilibrium thermodynamics and suggest a general mechanism governing the depth-dependent distribution of light elements within Earth's inner core.

physics.geo-ph↗

arXiv2025

Novel phases in the Fe-Si-O system at terapascal pressures

The Fe-Si-O ternary system, central to modeling the interiors of terrestrial planets, remains poorly constrained at Terapascal (TPa) pressures characteristic of super-Earth mantles. Using a combination of crystal-structure prediction and ab initio calculations, we identify three ternary compounds stable near 1 TPa: P3 FeSiO4, P3 Fe4Si5O18, and P-3 FeSi2O6. The first two phases are thermodynamically stable at low temperatures, whereas P-3 FeSi2O6 becomes favored above approximately 2000 K. All three are metallic, paramagnetic, and adopt pseudo-binary arrangements derived from the FeO2 and SiO2 end-member structures. Their crystal structures emerge through substitutions of Fe for Si in Fe2P-type SiO2 or of Si for Fe in Pnma-type FeO2, the stable elemental oxides at ~1 TPa. This structural continuity suggests that Fe preferentially substitutes for Si in the canonical Mg-silicates expected at TPa pressures. Notably, these new pseudo-binaries accommodate Fe in six- and nine-fold coordination, in contrast to the eight-fold cubic coordination found in FeO at similar pressures. The thermodynamic conditions under which these phases form from FeO2 and SiO2 mixtures are clarified through quasi-harmonic free-energy calculations. These phases imply a fundamentally different pattern of Fe incorporation into Mg-silicates at TPa pressures compared with that inferred for Earth's mantle, i.e., mainly [Fe]Mg. Their stability may trigger silicate dissociation into oxides ((Mg,Fe)2(Si,Fe)O4 -> 2(Mg,Fe)O + (Si,Fe)O2) at pressures below ~3 TPa, as expected in the Mg-Si-O system, with the extent of dissociation governed by iron content.

cond-mat.mtrl-sci↗

arXiv2025

Prediction of Li3Fe8B8 compound with rapid one-dimensional ion diffusion channels

Using a computational crystal structure search in the Li-Fe-B ternary system, we predict a stable phase of Li3Fe8B8, featuring 1D channels that enable rapid Li-ion transport. Ab initio molecular dynamics simulations show that the Li-ion diffusion coefficient in Li3Fe8B8 surpasses that of common electrode and conductive additive materials by several orders of magnitude. The high diffusion in Li3Fe8B8 can be explained by the Frenkel-Kontorova model, which describes an incommensurate state between the Li diffusion chain and the periodic potential field caused by the FeB backbone structure. The favorable lithium-ion diffusivity and mechanical properties of Li3Fe8B8 make it a promising conductive additive for battery materials. Its itinerant ferromagnetism also offers a platform for exploring correlated-electron magnetism and spin-dependent phenomena.

cond-mat.mtrl-sci↗

arXiv2025

AuthSim: Towards Authentic and Effective Safety-critical Scenario Generation for Autonomous Driving Tests

Generating adversarial safety-critical scenarios is a pivotal method for testing autonomous driving systems, as it identifies potential weaknesses and enhances system robustness and reliability. However, existing approaches predominantly emphasize unrestricted collision scenarios, prompting non-player character (NPC) vehicles to attack the ego vehicle indiscriminately. These works overlook these scenarios' authenticity, rationality, and relevance, resulting in numerous extreme, contrived, and largely unrealistic collision events involving aggressive NPC vehicles. To rectify this issue, we propose a three-layer relative safety region model, which partitions the area based on danger levels and increases the likelihood of NPC vehicles entering relative boundary regions. This model directs NPC vehicles to engage in adversarial actions within relatively safe boundary regions, thereby augmenting the scenarios' authenticity. We introduce AuthSim, a comprehensive platform for generating authentic and effective safety-critical scenarios by integrating the three-layer relative safety region model with reinforcement learning. To our knowledge, this is the first attempt to address the authenticity and effectiveness of autonomous driving system test scenarios comprehensively. Extensive experiments demonstrate that AuthSim outperforms existing methods in generating effective safety-critical scenarios. Notably, AuthSim achieves a 5.25% improvement in average cut-in distance and a 27.12% enhancement in average collision interval time, while maintaining higher efficiency in generating effective safety-critical scenarios compared to existing methods. This underscores its significant advantage in producing authentic scenarios over current methodologies.

cs.RO↗

arXiv2024

Ab initio superionic-liquid phase diagram of Fe1-xOx under Earth's inner core conditions

The superionic state is a phase of matter in which liquid-like ionic mobility coexists with a solid crystalline lattice. Recently identified in Earth's inner core (IC), this state has attracted considerable attention for its unique kinetic behavior and geophysical implications. However, the ab initio phase diagram describing the equilibrium between the superionic phase and the liquid solution under core conditions remains largely unexplored. Here, we present a thermodynamic approach to compute the Gibbs free energy and construct the ab initio superionic-liquid phase diagram for the Fe1-xOx system under IC conditions. We find that oxygen forms superionic states in both hcp and bcc Fe phases, with a pronounced influence on cooperative diffusion of iron in the bcc lattice. The stability fields of these superionic phases are sensitive to oxygen stoichiometry. The presence of superionic states leads to a higher oxygen concentration in the IC than previously estimated. Our work establishes a framework for investigating superionic-liquid equilibria under extreme conditions.

physics.geo-ph↗

arXiv2024

High-throughput screening for boride superconductors

A high-throughput screening using density functional calculations is performed to search for stable boride superconductors from the existing materials database. The workflow employs the fast frozen phonon method as the descriptor to evaluate the superconducting properties quickly. 23 stable candidates are identified from the screening. For almost all found binary compounds, the superconductivity was obtained earlier experimentally or computationally. For ternary borides, previous studies are very limited. Our extensive search among ternary systems confirmed superconductivity in known systems and found several new compounds. Among these discovered superconducting ternary borides, Ta(MoB)$_2$ shows the highest superconducting temperature of ~12K. Most predicted compounds were synthesized previously; therefore, our predictions can be examined experimentally. Our work also demonstrates that the boride systems can have diverse structural motifs that lead to superconductivity.

cond-mat.mtrl-sci↗

arXiv2023

Effect of Doping on the phase stability and Superconductivity in LaH10

We present a computational investigation into the effects of chemical doping with 15 different elements on phase stability and superconductivity in the LaH10 structure. Most doping elements were found to induce softening of phonon modes, enhancing electron-phonon coupling and improving critical superconducting temperature while weakening dynamical stability. Unlike these dopants, Ce was found to extend the range of dynamical stability for LaH10 by eliminating the van Hove singularity near the Fermi level. The doped compound, La0.75Ce0.25H10, maintains high-temperature superconductivity. We also demonstrate that different Ce doping configurations in the LaH10 structure have a minimal effect on energetic stability and electron-phonon coupling strength. Our findings suggest that Ce is a promising dopant to stabilize LaH10 at lower pressures while preserving its high-temperature superconductivity.

cond-mat.supr-con↗