Molecular Dynamics Simulations of Water in Confined Surfaces.

The freeze-thaw cycles of water in confined media, such as soil pores are necessary for proper infrastructure development in cold regions experiencing large variations in temperature as a result of climate change. In this project we use the ML-mW model of water in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to try and uncover some poorly understood qualities of confined water. The coarse-grained ML-mW model was chosen over other water models, due to its superb freezing behavior and its low computational load which allows us to simulate many more water molecules than would otherwise be possible in an atomistic simulation. This model treats an H₂O molecule as a single coarse bead and does not include the computationally expensive electrostatic effects. Previous literature shows that in confinement ice nucleation is dependent less on the hydrophilicity/hydrophobicity of the wall surface and more on the orientation and structure of the walls. We create simulations of water confined between walls of alpha-quartz crystalline silica and amorphous silica and compare the ice crystallinity, the atomic density, the enthalpy of freezing and the specific heat capacity of freezing. The Tersoff potential was used to simulate the interactions between the SiO2 wall atoms, and a Nose-Hoover ensemble was decided upon for our calculations in order to maintain consistency with previous literature. These results will allow us to understand the fundamental principles of ice formation in confined systems.