Berlin 2024 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 15: Phase Transformations II

MM 15.1: Talk

Monday, March 18, 2024, 16:45–17:00, C 230

Quantum hydrogen bond symmetrization in water ice and sulfur hydride — •Marco Cherubini and Michele Casula — Institut de Minéralogie, de Physique de Matériaux et de Cosmochimie, CNRS, Paris, France

Hydrogen bond symmetrization, influenced by the quantum nature of protons, is expected in various compounds. Nuclear quantum fluctuations diminish the boundary between symmetric and asymmetric phases by several gigapascals. Here, we investigate water ice and sulfur hydride, compounds exhibiting hydrogen bond symmetrization and sharing deep analogies. We use path integral molecular dynamics and the self-consistent harmonic approximation in combination with Quantum Monte Carlo, ab initio calculations, and machine learning potentials to solve the nuclear and electronic problems. In water ice, hydrogen bond symmetrization is a long-debated issue because of the lack of univocal experimental signatures. We describe, for the first time, the strong temperature dependence of the critical pressure in the classical regime, showing that quantum effects are so strong as to completely cover the thermal fluctuations, reducing the phase boundary by over 50 GPa. Importantly, we prove that proton disorder minimally influences quantum symmetrization. Sulfur hydride has been widely studied for its superconductivity, with its maximum critical temperature (200 K) previously believed to be associated with hydrogen bond symmetrization. Indeed, we prove that it is related to the transition from the symmetric phase to a phase characterized by disordered local moments, and that the asymmetric phase is reached at much lower pressures.

Keywords: Hydrogen; Nuclear quantum effects; High pressure physics; Self-consistent harmonic approximation; Path integral molecular dynamics