Local order parameters for use in driving homogeneous ice nucleation with all-atom models of water

TL;DR

This paper introduces a local order parameter for simulating and driving homogeneous ice nucleation in all-atom water models, enabling better tracking and forcing of ice growth in supercooled water, though challenges remain due to slow dynamics.

Contribution

A novel local order parameter based on Steinhardt-Ten Wolde approach is developed for use in all-atom water models to study ice nucleation.

Findings

The order parameter can effectively track and drive ice nucleation.

Ice growth dynamics are very slow in supercooled all-atom water simulations.

Computing free energy landscapes and nucleation rates remains challenging.

Abstract

We present a local order parameter based on the standard Steinhardt-Ten Wolde approach that is capable both of tracking and of driving homogeneous ice nucleation in simulations of all-atom models of water. We demonstrate that it is capable of forcing the growth of ice nuclei in supercooled liquid water simulated using the TIP4P/2005 model using overbiassed umbrella sampling Monte Carlo simulations. However, even with such an order parameter, the dynamics of ice growth in deeply supercooled liquid water in all-atom models of water are shown to be very slow, and so the computation of free energy landscapes and nucleation rates remains extremely challenging.