Point defects at the ice (0001) surface
- 30 June 2010
- journal article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 107 (28), 12429-12434
- https://doi.org/10.1073/pnas.1001087107
Abstract
Using density functional theory we investigate whether intrinsic defects in ice surface segregate. We predict that hydronium, hydroxide, and the Bjerrum L- and D-defects are all more stable at the surface. However, the energetic cost to create a D-defect at the surface and migrate it into the bulk crystal is smaller than its bulk formation energy. Absolute and relative segregation energies are sensitive to the surface structure of ice, especially the spatial distribution of protons associated with dangling hydrogen bonds. It is found that the basal plane surface of hexagonal ice increases the bulk concentration of Bjerrum defects, strongly favoring D-defects over L-defects. Dangling protons associated with undercoordinated water molecules are preferentially injected into the crystal bulk as Bjerrum D-defects, leading to a surface dipole that attracts hydronium ions. Aside from the disparity in segregation energies for the Bjerrum defects, we find the interactions between defect species to be very finely balanced; surface segregation energies for hydronium and hydroxide species and trapping energies of these ionic species with Bjerrum defects are equal within the accuracy of our calculations. The mobility of the ionic hydronium and hydroxide species is greatly reduced at the surface in comparison to the bulk due to surface sites with high trapping affinities. We suggest that, in pure ice samples, the surface of ice will have an acidic character due to the presence of hydronium ions. This may be important in understanding the reactivity of ice particulates in the upper atmosphere and at the boundary layer.Keywords
This publication has 34 references indexed in Scilit:
- Hydroxide trapped in the interior of ice: a computational studyPhysical Chemistry Chemical Physics, 2009
- Proton order in the ice crystal surfaceProceedings of the National Academy of Sciences of the United States of America, 2008
- On the Trapping of Bjerrum Defects in Ice Ih: The Case of the Molecular VacancyThe Journal of Physical Chemistry B, 2007
- Efficient and accurate three-dimensional Poisson solver for surface problemsThe Journal of Chemical Physics, 2007
- Water surface is acidicProceedings of the National Academy of Sciences of the United States of America, 2007
- Structure and Energetics of Molecular Point Defects in IcePhysical Review Letters, 2006
- Orientational Defects in Ice Ih: An Interpretation of Electrical Conductivity MeasurementsPhysical Review Letters, 2006
- Quickstep: Fast and accurate density functional calculations using a mixed Gaussian and plane waves approachComputer Physics Communications, 2005
- Unit cells for the simulation of hexagonal iceThe Journal of Chemical Physics, 1997
- The Structure and Entropy of Ice and of Other Crystals with Some Randomness of Atomic ArrangementJournal of the American Chemical Society, 1935