Structure and Dynamics of the Hydration Shells of the Al3+ Ion
First principles simulations of the hydration shells surrounding Al3+ ions are reported for temperatures near 300oC. The predicted six waters in the octahedral first hydration shell were found to be trigonally coordinated via hydrogen-bonds to 12 second shell waters in agreement with the putative structure used to analyze the X-ray data, but in disagreement with results reported from conventional molecular dynamics using two- and three-body potentials. Bond lengths and angles of the water molecules in the first and second hydration shell and the average radii of these shells also agreed very well with the results of the X-ray analysis. Water transfers into and out of the 2nd solvation shell were observed to occur on a picosecond (ps) time scale via a dissociative mechanism. Beyond the second shell the bonding pattern substantially returned to the tetrahedral structure of bulk water. Most of the simulations were done with 64 solvating waters (20 ps). Limited simulations with 128 waters (5 ps) were also carried out. Results agreed as to the general structure of the solvation region and were essentially the same for the first and second shell. However, there were differences in hydrogen-bonding and Al-O radial distribution function in the region just beyond the second shell. At the end of the second shell a nearly zero minimum in the Al-O radial distribution was found for the 128 water system. This minimum is less pronounced minimum was found for the 64 water system, which may indicate that sizes larger than 64 may be required to reliably predict behavior in this region,
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 908937
- Report Number(s):
- PNNL-SA-52973; JCPSA6; 3564a; 20900; KC0303020; TRN: US200722%%820
- Journal Information:
- Journal of Chemical Physics, 126(10):Art.no.104505, Vol. 126, Issue 10; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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