Characterizing Anharmonic Behaviours: The Curious Case of CsH₃
ORAL
Abstract
The characterization of high-pressure metal–hydrogen systems, known as superhydrides, has attracted significant attention due to their potential to form hydrogen-rich compositions with a variety of unconventional properties, ranging from extremely high-temperature superconductivity to strong anharmonicity and exotic hydrogen bonding motifs.
In superhydrides, the combined effects of chemical doping, quantum anharmonicity, and high pressure act to weaken molecular hydrogen bonds. The interplay of these effects creates conditions for the emergence of complex phenomena that are, from a theoretical perspective, challenging to characterize due to the presence of shallow energy barriers and pronounced quantum behavior. For example, in rubidium pentahydride (RbH₅)[1], the structure comprises Rb⁺ cations, quasimolecular H₂ units, and linear H₃⁻ anions.
In this talk, we investigate the properties of the previously predicted cesium trihydride (CsH₃)[2] compound over a pressure range between 10 GPa and 100 GPa, comparing our theoretical results with newly obtained experimental data. Our findings emphasize the challenges in accurately characterizing the dynamic properties of CsH₃ using standard density functional perturbation theory (DFPT) methods, and we further demonstrate the limitations and failure of the stochastic self-consistent harmonic approximation (SSCHA)[3] in this context.
Overall, our work proposes a valuable case study that contribute to the development and benchmarking of advanced theoretical methods for understanding quantum materials under extreme conditions.
[1] Phys. Rev. Lett. 134, 196102 (2025)
[2] Inorg. Chem. 51, 17, 9333–9342 (2012)
[3] J. Phys.: Condens. Matter 33 363001 (2021)
In superhydrides, the combined effects of chemical doping, quantum anharmonicity, and high pressure act to weaken molecular hydrogen bonds. The interplay of these effects creates conditions for the emergence of complex phenomena that are, from a theoretical perspective, challenging to characterize due to the presence of shallow energy barriers and pronounced quantum behavior. For example, in rubidium pentahydride (RbH₅)[1], the structure comprises Rb⁺ cations, quasimolecular H₂ units, and linear H₃⁻ anions.
In this talk, we investigate the properties of the previously predicted cesium trihydride (CsH₃)[2] compound over a pressure range between 10 GPa and 100 GPa, comparing our theoretical results with newly obtained experimental data. Our findings emphasize the challenges in accurately characterizing the dynamic properties of CsH₃ using standard density functional perturbation theory (DFPT) methods, and we further demonstrate the limitations and failure of the stochastic self-consistent harmonic approximation (SSCHA)[3] in this context.
Overall, our work proposes a valuable case study that contribute to the development and benchmarking of advanced theoretical methods for understanding quantum materials under extreme conditions.
[1] Phys. Rev. Lett. 134, 196102 (2025)
[2] Inorg. Chem. 51, 17, 9333–9342 (2012)
[3] J. Phys.: Condens. Matter 33 363001 (2021)
*Funding for this research was provided by the National Science Foundation, under award DMR-2136038 and the US Department of Energy, Office of Science, Fusion Energy Sciences under award DE-SC0020340, entitled High Energy Density Quantum Matter. Calculations were performed at the Center for Computational Research at the State University of New York at Buffalo (https://hdl.handle.net/10477/79221).
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Presenters
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Francesco Belli
- State Univ of NY - Buffalo