What is it about?

We introduce a new approach to compute lattice vibrations in materials where both electrons and nuclei must be treated as quantum particles. Those are usually hydrogen-rich materials, such as the new family of superconducting hydrides, featuring the highest superconducting critical temperatures. Nuclear quantum effects make lattice vibrations very hard to compute, due to strong anharmonicity affecting these materials, which leads to strongly interacting phonons. Our framework allows for a reliable estimate of the lowest-lying phonon excitations even in this hardest situation, and for a robust comparison against experimental infrared and Raman spectroscopies in this class of materials.

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Why is it important?

Our new method is suited to compute phonons in quantum crystals. It is able to accurately capture the first phonon excitation energies, even in case of strong nuclear quantum effects and strong anharmonicity. The computational scheme we devised increases by an order of magnitude the efficiency of the path integral sampling of vibrational modes, by allowing accurate calculations of anharmonic phonons in quantum crystals entirely from first principles.

Perspectives

This work opens the possibility of computing accurate phonons in quantum materials such as super-hydrides, which show record breaking values for the superconducting critical temperature, reaching almost room temperature superconductivity. In these materials, phonons are key to understand and predict the superconducting phase.

Michele Casula
Sorbonne Université

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This page is a summary of: Probing anharmonic phonons by quantum correlators: A path integral approach, The Journal of Chemical Physics, June 2021, American Institute of Physics, DOI: 10.1063/5.0050450.
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