Molecular reordering processes on ice (0001) surfaces from long timescale simulations

Area of Science:

• Surface Science
• Computational Chemistry
• Materials Science

Background:

• Hexagonal ice surfaces play a role in atmospheric chemistry and climate.
• Understanding molecular behavior on ice surfaces is crucial for various scientific disciplines.

Purpose of the Study:

• To investigate molecular reordering processes on hexagonal ice (0001) surfaces.
• To compare the behavior of proton-disordered and ordered (Fletcher) surfaces.
• To identify potential atmospheric reaction sites on ice surfaces.

Main Methods:

• Long timescale adaptive kinetic Monte Carlo simulations (up to 50 μs).
• Force field simulations for flexible molecules at 100 K.
• Density functional theory and ab initio polarizable potential function calculations for force field refinement.

Main Results:

• Concerted reorientation (flipping) of surface molecules and interstitial defect formation observed.
• Proton-disordered surfaces exhibit significant roughening.
• The ordered Fletcher surface is more stable, showing localized molecular rearrangements instead of roughening.
• Fletcher surface molecules can form interstitial defects, potentially acting as reaction sites.

Conclusions:

• The flipping process promotes proton order and surface stabilization, supporting Fletcher-like ordering on low-temperature ice surfaces.
• Proton-disordered patches can induce local surface reconstructions.
• Interstitial defects on the Fletcher surface may serve as active sites for atmospheric chemical reactions.