arXiv subjects

Aurélie Champagne

Publications and source records attributed to Aurélie Champagne.

8 recordsLinked to original sources

arXiv2026

A strategic roadmap for an atomistic machine-learning ecosystem

Data-driven machine learning (ML) techniques have become an essential tool in many domains of science. Their application to atomistic simulations of matter is particularly widespread and impactful. This success is due largely to the existence of a well-developed and established physics-based modeling framework, ranging from first-principles electronic-structure calculations to molecular dynamics and statistical sampling, into which ML was integrated naturally to reshape long-standing trade-offs between accuracy, efficiency, and scale. Nevertheless, this integration raises both conceptual and practical challenges, from choosing between data-centric and physics-based modeling approaches to adapting established software stacks to modern hardware accelerators and ML libraries. As the field evolves rapidly, fueled in part by widespread enthusiasm but also by tangible impact, it seems appropriate to take a moment to consider the current state of the art and open challenges, and reflect on what can be done to better coordinate efforts across the community. With this goal in mind, several members of this community met in Lausanne in January 2026 at CECAM to discuss algorithms, models, software and hardware infrastructure, and the most promising scientific applications that have become possible thanks to the use of artificial intelligence in atomic-scale simulations. This strategic roadmap paper summarizes the outcomes of these discussions, suggesting some long-term goals, and some concrete actions, to establish a healthy, sustainable and impactful atomistic ML ecosystem.

physics.chem-ph↗

arXiv2026

Predicting Crystal Structures and Ionic Conductivities in Li$_{3}$YCl$_{6-x}$Br$_{x}$ Halide Solid Electrolytes Using a Fine-Tuned Machine Learning Interatomic Potential

Understanding ionic transport in halide solid electrolytes is essential for advancing next-generation solid-state batteries. This work demonstrates the effectiveness of fine-tuning the Crystal Hamiltonian Graph Network (CHGNet) universal machine learning interatomic potential to accurately predict total energies, relaxed geometries, and lithium-ion dynamics in the ternary halide family Li$_{3}$YCl$_{6-x}$Br$_{x}$ (LYCB). Starting from experimentally refined disordered structures of Li$_{3}$YCl$_{6}$ and Li$_{3}$YBr$_{6}$, we present a strategy for generating ordered structural models through systematic enumeration and energy ranking, providing realistic structural models. These serve as initial configurations for an iterative fine-tuning workflow that integrates molecular dynamics simulations and static density functional theory calculations to achieve near-ab initio accuracy at four orders of magnitude lower computational cost. We further reveal the influence of composition (varied x) on the predicted phase stability and ionic conductivity in LYCB, demonstrating the robustness of our approach for modeling transport properties in complex solid electrolytes.

cond-mat.mtrl-sci↗

arXiv2025

Tunable electronic energy level alignment and exciton diversity in organic-inorganic van der Waals heterostructures

van der Waals stacking of two-dimensional (2D) materials offers a powerful platform for engineering material interfaces with tailored electronic and optical properties. While most van der Waals multilayers have featured inorganic monolayers, incorporating molecular monolayers introduces new degrees of tunability and functionality. Here, we investigate hybrid bilayers composed of atomically thin perylene-based molecular crystals interfaced with monolayer transition metal dichalcogenides (TMDs), specifically MoS2 and WS2. Using ab initio many-body perturbation theory within the GW approximation and the Bethe-Salpeter equation approach, we predict emergent properties beyond those of the isolated constituent systems. Notably, we find substantial renormalization of monolayer molecular crystal band gap due to TMD-induced polarization. Furthermore, by varying the TMD monolayer, we demonstrate tuning of the energy level alignment of the bilayer and subsequent control over a diversity of lowest-energy excitons, which include strongly bound hybrid excitons and long-lived charge-transfer excitons. These findings establish organic-inorganic van der Waals heterostructures as a promising class of materials for tunable optoelectronic devices and quantum excitonic phenomena, expanding the design space for low-dimensional systems.

cond-mat.mtrl-sci↗

arXiv2025

The reliability of hybrid functionals for accurate fundamental and optical gap prediction of bulk solids and surfaces

Hybrid functionals have been considered insufficiently reliable for the prediction of band gaps in solids and surfaces. We revisit this issue with a new generation of optimally-tuned range-separated hybrid functionals, focusing on the reconstructed Si(111)-(2x1) and Ge(111)-(2x1) surfaces. We show that certain hybrid functionals can accurately predict the surface-state and bulk fundamental and optical gaps, as well as projected band structures of these surfaces, by combining ground-state and time-dependent density functional theory.

cond-mat.mtrl-sci↗

arXiv2025

Bright hybrid excitons in molecularly tunable bilayer crystals

Bilayer crystals, built by stacking crystalline monolayers, generate interlayer potentials that govern excitonic phenomena but are constrained by fixed covalent lattices and orientations. Replacing one layer with an atomically thin molecular crystal overcomes this limitation, as diverse functional groups enable tunable molecular lattices and interlayer potentials, tailoring a wide range of excitonic properties. Here, we report hybrid excitons in four-atom-thick hybrid bilayer crystals (HBCs), directly synthesized with single-crystalline perylene diimide (PDI) molecular crystal atop WS2 monolayers. These excitons arise from a hybridized bilayer band structure, revealed by lattice-scale first-principles calculations, inheriting properties from both monolayers. They exhibit bright photoluminescence with near-unity polarization above and below the WS2 bandgap, along with spectral signatures of exciton delocalization, supported by theory, while their energies and intensities are tuned by modifying the HBC composition by synthesis. Our work introduces a molecule-based 2D quantum materials platform for bottom-up design and control of optoelectronic properties.

cond-mat.mtrl-sci↗

arXiv2025

Molecular tuning of excitons in four-atom-thick hybrid bilayer crystals

Bilayer crystals, formed by stacking monolayers of two-dimensional (2D) crystals, create interlayer potentials that govern excitonic phenomena but are constrained by their fixed covalent lattices. Replacing one layer with an atomically thin molecular crystal overcomes this limitation, as precise control of functional groups enables tunable 2D molecular lattices and, consequently, electronic structures. Here, we report molecular tuning of lattices and excitons in four-atom-thick hybrid bilayer crystals (HBCs), synthesized as monolayers of perylene-based molecular and transition metal dichalcogenide (TMD) single crystals. In HBCs, we observe an anisotropic photoluminescence signal exhibiting characteristics of both molecular and TMD excitons, directly tuned by molecular geometry and HBC composition. Ab initio calculations reveal that this anisotropic emission arises from hybrid excitons, which inherit properties from both layers through a hybridized bilayer band structure. Our work establishes a synthetically derived, molecule-based 2D quantum materials platform with the potential for engineering interlayer potentials.

cond-mat.mtrl-sci↗

arXiv2023

Rydberg Excitons and Trions in Monolayer MoTe$_2$

Monolayer transition metal dichalcogenide (TMDC) semiconductors exhibit strong excitonic optical resonances which serve as a microscopic, non-invasive probe into their fundamental properties. Like the hydrogen atom, such excitons can exhibit an entire Rydberg series of resonances. Excitons have been extensively studied in most TMDCs (MoS$_2$, MoSe$_2$, WS$_2$ and WSe$_2$), but detailed exploration of excitonic phenomena has been lacking in the important TMDC material molybdenum ditelluride (MoTe$_2$). Here, we report an experimental investigation of excitonic luminescence properties of monolayer MoTe$_2$ to understand the excitonic Rydberg series, up to 3s. We report significant modification of emission energies with temperature (4K to 300K), quantifying the exciton-phonon coupling. Furthermore, we observe a strongly gate-tunable exciton-trion interplay for all the Rydberg states governed mainly by free-carrier screening, Pauli blocking, and band-gap renormalization in agreement with the results of first-principles GW plus Bethe-Salpeter equation approach calculations. Our results help bring monolayer MoTe$_2$ closer to its potential applications in near-infrared optoelectronics and photonic devices.

cond-mat.mes-hall↗

arXiv2018

Electronic and vibrational properties of V$_2$C-based MXenes: from experiments to first-principles modeling

In the present work, the electronic and vibrational properties of both pristine V$_2$C and fully-terminated V$_2$CT$_2$ (where T = F, O, OH) 2D monolayers are investigated using density functional theory. Firstly, the atomic structures of V$_2$C-based MXene phases are optimized and their respective dynamical stabilities are discussed. Secondly, electronic band structures are computed indicating that V$_2$C is metallic as well as all the corresponding functionalized systems. Thirdly, the vibrational properties (phonon frequencies and spectra) of V$_2$C-based MXenes are computed thanks to density functional perturbation theory and reported for the first time. Both Raman (E$_g$, A$_{1g}$) and infrared active (E$_u$, A$_{2u}$) vibrational modes are predicted \textit{ab initio} with the aim to correlate the experimental Raman peaks with the calculated vibrational modes and to assign them with specific atomic motions. The effect of the terminal groups on the vibrational properties is emphasized as well as on the presence and position of the corresponding Raman peaks. Our results provide new insights for the identification and characterization of V$_2$C-based samples using Raman spectroscopy.

physics.chem-ph↗