Isotope Effects and the Negative Thermal Expansion Phenomena in Ice and Water

TL;DR

This paper investigates the isotope effects and negative thermal expansion in ice and water, revealing the quantum mechanical origins of these phenomena through theoretical modeling of phonons and hydrogen bonding.

Contribution

It introduces a quantum mechanical approach to explain isotope effects and NTE in ice and water, highlighting the role of nuclear quantum processes.

Findings

Unusual isotope effects arise from competition between zero-point and thermal phonons.

Quantum mechanical processes are crucial in understanding NTE and VIE in ice and water.

Hydrogen bonding dynamics are influenced by isotope substitution, affecting thermal properties.

Abstract

H2O is a unique substance with exceptional thermal properties arising from the subtle interplay between its electronic, phononic, and structural degrees of freedom. Of particular interest in H2O are the negative thermal expansion (NTE) phenomena, observed in its solid phase (ice) at low temperature, and in its liquid phase (water) near the freezing temperature. Furthermore, ice and water exhibit the abnormal volume isotope effect (VIE), where volume expansions occur when replacing H with its heavier isotope, deuterium (D). In order to capture more conceptual and intuitive understanding of intriguing NTE and VIE phenomena in ice and water, we have explored isotope effects in their NTE and melting properties by employing a type of Born-Oppenheimer-approximation approach and the Lindemann criterion. Our findings demonstrate that unusual isotope effects in these phenomena stem from competition between zero-point-energy phonons, thermal phonons, and the hydrogen bonding in H2O. All these components originate from nuclear quantum mechanical (QM) processes, revealing that QM physics plays a crucial role in the seemingly classical ice/water systems.