First Principles Simulations fo the Supercritical Behavior of Ore Forming Fluids [electronic resource].
- Published
- Washington, D.C. : United States. Dept. of Energy, 2013.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy. - Additional Creators
- University of California (System). Regents, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
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- Summary
- Abstract of Selected Research Progress: I. First-principles simulation of solvation structure and deprotonation reactions of ore forming metal ions in very nonideal solutions: Advances in algorithms and computational performance achieved in this grant period have allowed the atomic level dynamical simulation of complex nanoscale materials using interparticle forces calculated directly from an accurate density functional solution to the electronic SchrÃÂÃÂÃÂÃÂÃÂÃÂÃÂödinger equation (ab-initio molecular dynamics, AIMD). Focus of this program was on the prediction and analysis of the properties of environmentally important ions in aqueous solutions. AIMD methods have provided chemical interpretations of these very complex systems with an unprecedented level of accuracy and detail. The structure of the solvation region neighboring a highly charged metal ion (e.g., 3+) in an aqueous solution is very different from that of bulk water. The many-body behaviors (polarization, charge transfer, etc.) of the ion-water and water-water interactions in this region are difficult to capture with conventional empirical potentials. However, a large numbers of waters (up to 128 waters) are required to fully describe chemical events in the extended hydrations shells and long simulation times are needed to reliably sample the system. Taken together this makes simulation at the 1st principles level a very large computational problem. Our AIMD simulation results using these methods agree with the measured octahedral structure of the 1st solvation shell of Al3+ at the 1st shell boundary and a calculated radius of 1.937ÃÂÃÂÃÂÃÂÃÂÃÂÃÂà(exp. 1.9ÃÂÃÂÃÂÃÂÃÂÃÂÃÂà). Our calculated average 2nd shell radius agrees remarkably well with the measured radius, 4.093 ÃÂÃÂÃÂÃÂÃÂÃÂÃÂàcalculated vs. the measured value of 4.0-4.15 ÃÂÃÂÃÂÃÂÃÂÃÂÃÂà. Less can be experimentally determined about the structure of the 2nd shell. Our simulations show that this shell contains roughly 12 water molecules, which are trigonally coordinated to the 1st shell waters. This structure cannot be measured directly. However, the number of 2nd shell water molecules predicted by the simulation is consistent with experimental estimates. Tetrahedral bulk water coordination reappears just after the 2nd shell. Simulations with 128 waters are close to the maximum size that can effectively be performed with present day methods. While the time scale of our simulation are not long enough to observe transfers of waters from the 1st to the 2nd shell, we do see transfers occurring on a picosecond time scale between the 2nd shell and 3rd shell via an associative mechanism. This is faster than, but consistent with, the results of measurements on the more tightly bound Cr3+ system. For high temperature simulations, proton transfers occur in the solvation shells leading to transient hydrolysis species. The reaction coordinate for proton transfer involves the coordinates of neighboring solvent waters as in the Grotis mechanism for proton transfer in bulk water. Directly removing a proton from the hexaqua Al3+ ion leads to a much more labile solvation shell and to a five coordinated Al3+ ion. This is consistent with very recent rate measurements of ligand exchange and the conjugate base labilization effect. For the Al3+-H2O system results for high but subcritical temperatures are qualitatively similar to room temperature simulations. However, preliminary simulations for supercritical temperatures (750K) suggest that there may be a dramatic change in behavior in the hydration structure of ions for these temperatures. For transition metal ions the presence of d valence electrons plays a significant role in the behavior of the system. Our preliminary results for the Fe3+ ion suggest that this ion which is larger radius than the Al3+ ion has somewhat less rigid 1st and 2nd solvation shell. II. Gibbs Ensemble Monte Carlo Simul...
- Report Numbers
- E 1.99:1074367
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- Other Subject(s)
- Note
- Published through SciTech Connect.
04/19/2013.
Weare, John H. - Type of Report and Period Covered Note
- Final; 06/15/2002 - 12/31/2005
- Funding Information
- FG02-02ER15311
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