@article{20492,
  abstract     = {The glassy thermal conductivities observed in crystalline inorganic perovskites such as Cs3Bi2I6Cl3 are perplexing and lacking theoretical explanations. Here, we first experimentally measure its thermal transport behavior from 20 to 300 K, after synthesizing Cs3Bi2I6Cl3 single crystals. Using path-integral molecular dynamics simulations driven by machine learning potentials, we reveal that Cs3Bi2I6Cl3 has large lattice distortions at low temperatures, which may be related to the large atomic size mismatch. Employing the Wigner formulation of thermal transport, we reproduce theexperimental thermal conductivities based on lattice-distorted structures. This studythus provides a framework for predicting and understanding glassy thermal transportin materials with strong lattice disorder.},
  author       = {Zeng, Zezhu and Fan, Zheyong and Simoncelli, Michele and Chen, Chen and Liang, Ting and Chen, Yue and Thornton, Geoff and Cheng, Bingqing},
  issn         = {1091-6490},
  journal      = {Proceedings of the National Academy of Sciences},
  number       = {41},
  pages        = {e2415664122},
  publisher    = {National Academy of Sciences},
  title        = {{Lattice distortion leads to glassy thermal transport in crystalline Cs3Bi2I6Cl3}},
  doi          = {10.1073/pnas.2415664122},
  volume       = {122},
  year         = {2025},
}

@article{20011,
  abstract     = {Heat transport in glasses over a wide temperature range is critical for applications in gate dielectrics and thermal insulators but remains poorly understood due to the challenges in modeling vibrational anharmonicity and configurational dynamics across the glass transition. Recent predictions show an unusual decrease in thermal conductivity (κ) with temperature in amorphous hafnia (a-HfO2), contrasting with the typical trend in glasses. Using molecular dynamics with a machine-learning-based neuroevolution potential, we compute κ of a-HfO2 from 50 K to 2000 K. At low temperatures, the Wigner transport equation captures both anharmonicity and quantum statistics. Above 1200 K, atomic diffusion invalidates the quasiparticle picture, and we resort to the Green–Kubo method to capture convective transport. We further extend the Wigner transport equation to supercooled a-HfO2, revealing the crucial role of low-frequency modes in facilitating heat transport. The computed κ, based on both Green–Kubo and Wigner transport theories, increases continuously with temperature up to 2000 K.},
  author       = {Zeng, Zezhu and Liang, Xia and Fan, Zheyong and Chen, Yue and Simoncelli, Michele and Cheng, Bingqing},
  issn         = {2639-4979},
  journal      = {ACS Materials Letters},
  pages        = {2695--2701},
  publisher    = {American Chemical Society},
  title        = {{Thermal transport of amorphous hafnia across the glass transition}},
  doi          = {10.1021/acsmaterialslett.5c00263},
  year         = {2025},
}

@article{20704,
  abstract     = {Generative models have advanced significantly in sampling material systems with continuous variables, such as atomistic structures. However, their application to discrete variables, like atom types or spin states, remains underexplored. In this work, we introduce a discrete flow matching model, tailored for systems with discrete phase-space coordinates (e.g., the Ising model or a multicomponent system on a lattice). This approach enables a single model to sample free energy surfaces over a wide temperature range with minimal training overhead, and the model generation is scalable to larger lattice sizes than those in the training set. We demonstrate our approach on the 2D Ising model, showing efficient and reliable free energy sampling. These results highlight the potential of flow matching for low-cost, scalable free energy sampling in discrete systems and suggest promising extensions to alchemical degrees of freedom in crystalline materials. The codebase developed for this work is openly available at https://github.com/tuoping/alchemicalFES.},
  author       = {Tuo, Ping and Zeng, Zezhu and Chen, Jiale and Cheng, Bingqing},
  issn         = {1549-9626},
  journal      = {Journal of Chemical Theory and Computation},
  number       = {22},
  pages        = {11427--11435},
  publisher    = {American Chemical Society},
  title        = {{Scalable multitemperature free energy sampling of classical Ising spin states}},
  doi          = {10.1021/acs.jctc.5c01248},
  volume       = {21},
  year         = {2025},
}

@article{15311,
  abstract     = {Materials with low thermal conductivity usually have complex crystal structures. Herein we experimentally find that a simple crystal structure material AgTlI2 (I4/mcm) owns an extremely low thermal conductivity of 0.25 W/mK at room temperature. To understand this anomaly, we perform in-depth theoretical studies based on ab initio molecular dynamics simulations and anharmonic lattice dynamics. We find that the unique atomic arrangement and weak chemical bonding provide a permissive environment for strong oscillations of Ag atoms, leading to a considerable rattling behaviour and giant lattice anharmonicity. This feature is also verified by the experimental probability density function refinement of single-crystal diffraction. The particularly strong anharmonicity breaks down the conventional phonon gas model, giving rise to non-negligible wavelike phonon behaviours in AgTlI2 at 300 K. Intriguingly, unlike many strongly anharmonic materials where a small propagative thermal conductivity is often accompanied by a large diffusive thermal conductivity, we find an unusual coexistence of ultralow propagative and diffusive thermal conductivities in AgTlI2 based on the thermal transport unified theory. This study underscores the potential of simple crystal structures in achieving low thermal conductivity and encourages further experimental research to enrich the family of materials with ultralow thermal conductivity.},
  author       = {Zeng, Zezhu and Shen, Xingchen and Cheng, Ruihuan and Perez, Olivier and Ouyang, Niuchang and Fan, Zheyong and Lemoine, Pierric and Raveau, Bernard and Guilmeau, Emmanuel and Chen, Yue},
  issn         = {2041-1723},
  journal      = {Nature Communications},
  publisher    = {Springer Nature},
  title        = {{Pushing thermal conductivity to its lower limit in crystals with simple structures}},
  doi          = {10.1038/s41467-024-46799-3},
  volume       = {15},
  year         = {2024},
}

@article{15052,
  abstract     = {Substrate induces mechanical strain on perovskite devices, which can result in alterations to its lattice dynamics and thermal transport. Herein, we have performed a theoretical investigation on the anharmonic lattice dynamics and thermal property of perovskite Rb2SnBr6 and Cs2SnBr6 under strains using perturbation theory up to the fourth-order terms and the unified thermal transport theory. We demonstrate a pronounced hardening of low-frequency optical phonons as temperature increases, indicating strong lattice anharmonicity and the necessity of adopting temperature-dependent interatomic force constants in the lattice thermal conductivity (
κL) calculations. It is found that the low-lying optical phonon modes of Rb2SnBr6 are extremely soft and their phonon energies are almost strain independent, which ultimately lead to a lower 
κL and a weaker strain dependence than Cs2SnBr6. We further reveal that the strain dependence of these phonon modes in the A2XB6-type perovskites weakens as their ibrational frequency decreases. This study deepens the understanding of lattice thermal transport in perovskites A2XB6 and provides a perspective on the selection of materials that meet the expected thermal behaviors in practical applications.},
  author       = {Cheng, Ruihuan and Zeng, Zezhu and Wang, Chen and Ouyang, Niuchang and Chen, Yue},
  issn         = {2469-9969},
  journal      = {Physical Review B},
  number       = {5},
  publisher    = {American Physical Society},
  title        = {{Impact of strain-insensitive low-frequency phonon modes on lattice thermal transport in AxXB6-type perovskites}},
  doi          = {10.1103/physrevb.109.054305},
  volume       = {109},
  year         = {2024},
}

@article{15359,
  abstract     = {Molecular dynamics (MD) simulations play an important role in understanding and engineering heat transport properties of complex materials. An essential requirement for reliably predicting heat transport properties is the use of accurate and efficient interatomic potentials. Recently, machine-learned potentials (MLPs) have shown great promise in providing the required accuracy for a broad range of materials. In this mini-review and tutorial, we delve into the fundamentals of heat transport, explore pertinent MD simulation methods, and survey the applications of MLPs in MD simulations of heat transport. Furthermore, we provide a step-by-step tutorial on developing MLPs for highly efficient and predictive heat transport simulations, utilizing the neuroevolution potentials as implemented in the GPUMD package. Our aim with this mini-review and tutorial is to empower researchers with valuable insights into cutting-edge methodologies that can significantly enhance the accuracy and efficiency of MD simulations for heat transport studies.},
  author       = {Dong, Haikuan and Shi, Yongbo and Ying, Penghua and Xu, Ke and Liang, Ting and Wang, Yanzhou and Zeng, Zezhu and Wu, Xin and Zhou, Wenjiang and Xiong, Shiyun and Chen, Shunda and Fan, Zheyong},
  issn         = {1089-7550},
  journal      = {Journal of Applied Physics},
  number       = {16},
  publisher    = {AIP Publishing},
  title        = {{Molecular dynamics simulations of heat transport using machine-learned potentials: A mini-review and tutorial on GPUMD with neuroevolution potentials}},
  doi          = {10.1063/5.0200833},
  volume       = {135},
  year         = {2024},
}

@article{14425,
  abstract     = {Water adsorption and dissociation processes on pristine low-index TiO2 interfaces are important but poorly understood outside the well-studied anatase (101) and rutile (110). To understand these, we construct three sets of machine learning potentials that are simultaneously applicable to various TiO2 surfaces, based on three density-functional-theory approximations. Here we show the water dissociation free energies on seven pristine TiO2 surfaces, and predict that anatase (100), anatase (110), rutile (001), and rutile (011) favor water dissociation, anatase (101) and rutile (100) have mostly molecular adsorption, while the simulations of rutile (110) sensitively depend on the slab thickness and molecular adsorption is preferred with thick slabs. Moreover, using an automated algorithm, we reveal that these surfaces follow different types of atomistic mechanisms for proton transfer and water dissociation: one-step, two-step, or both. These mechanisms can be rationalized based on the arrangements of water molecules on the different surfaces. Our finding thus demonstrates that the different pristine TiO2 surfaces react with water in distinct ways, and cannot be represented using just the low-energy anatase (101) and rutile (110) surfaces.},
  author       = {Zeng, Zezhu and Wodaczek, Felix and Liu, Keyang and Stein, Frederick and Hutter, Jürg and Chen, Ji and Cheng, Bingqing},
  issn         = {2041-1723},
  journal      = {Nature Communications},
  publisher    = {Springer Nature},
  title        = {{Mechanistic insight on water dissociation on pristine low-index TiO2 surfaces from machine learning molecular dynamics simulations}},
  doi          = {10.1038/s41467-023-41865-8},
  volume       = {14},
  year         = {2023},
}

@article{14605,
  abstract     = {The phonon transport mechanisms and ultralow lattice thermal conductivities (κL) in silver halide AgX (X=Cl,Br,I) compounds are not yet well understood. Herein, we study the lattice dynamics and thermal property of AgX under the framework of perturbation theory and the two-channel Wigner thermal transport model based on accurate machine learning potentials. We find that an accurate extraction of the third-order atomic force constants from largely displaced configurations is significant for the calculation of the κL of AgX, and the coherence thermal transport is also non-negligible. In AgI, however, the calculated κL still considerably overestimates the experimental values even including four-phonon scatterings. Molecular dynamics (MD) simulations using machine learning potential suggest an important role of the higher-than-fourth-order lattice anharmonicity in the low-frequency phonon linewidths of AgI at room temperature, which can be related to the simultaneous restrictions of the three- and four-phonon phase spaces. The κL of AgI calculated using MD phonon lifetimes including full-order lattice anharmonicity shows a better agreement with experiments.},
  author       = {Ouyang, Niuchang and Zeng, Zezhu and Wang, Chen and Wang, Qi and Chen, Yue},
  issn         = {2469-9969},
  journal      = {Physical Review B},
  number       = {17},
  publisher    = {American Physical Society},
  title        = {{Role of high-order lattice anharmonicity in the phonon thermal transport of silver halide AgX (X=Cl,Br, I)}},
  doi          = {10.1103/PhysRevB.108.174302},
  volume       = {108},
  year         = {2023},
}