# An improved interstitial-ice model for pure liquid water

## TL;DR

This paper refines the interstitial-ice model of liquid water by deriving parameters from NMR data, revealing significant vacancies and temperature-dependent interstitials, thus better explaining water's thermodynamic properties.

## Contribution

The authors improve the interstitial-ice model by using NMR data, revealing realistic vacancy concentrations and temperature dependence, addressing previous counter-intuitive results.

## Key findings

- Vacancy concentration at 0°C is 3.7%.
- Interstitial and vacancy concentrations increase linearly with temperature.
- The model explains thermodynamic data of water effectively.

## Abstract

The main idea of the interstitial-ice model is that liquid water consists of an intact hexagonal lattice with both vacant lattice positions and interstitial water molecules. Narten, Danford and Levy derived the model parameters from the X-ray diffraction patterns of liquid water. However, their results were counter-intuitive: their model had almost no vacancies, the interstitial concentration was temperature independent and the ice lattice was deformed resulting in extra anisotropy. To overcome these problems, we refined the model and derived the model parameters from the proton nuclear magnetic resonance frequency of pure water. Without any extra anisotropy, a significant concentration of vacancies was found (3.7% of the lattice positions at 0{\deg}C) and the concentration of both the vacancies and interstitials increased quasi linear with temperature (0.05 M/{\deg}C). This improved model successfully explains the thermodynamic data of water and is therefore a promising candidate for a coherent and analytical water model.