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Title: Structures and Energetics of (MgCO3 )n Clusters ( n ≤ 16)

There is significant interest in the role of carbonate minerals for the storage of CO2 and the role of prenucleation dusters in their formation. Global minima for (MgCO3)n (n ≤ 16) structures were optimized using a tree growth-hybrid genetic algorithm in conjunction with MNDO/MNDO/d semiempirical molecular orbital calculations followed by density functional theory geometry optimizations with the B3LYP functional. The most stable isomers for (MgCO3)n (n < 5) are approximately 2-dimensional. Mg can be bonded to one or two 0 atoms of a CO32-, and the 1-O bonding scheme is more favored as the cluster becomes larger. The average C-Mg coordination number increases as the cluster size increases, and at n = 16, the average C-Mg coordination number was calculated to be 5.2. The normalized dissociation energy to form monomers increases as n increases. At n = 16, the normalized dissociation energy is calculated to be 116.2 kcal/mol, as compared to the bulk value of 153.9 kcal/mol. The adiabatic reaction energies for the recombination reactions of (MgO)nclusters and CO2 to form (MgCO3)n were calculated. The exothermicity of the normalized recombination energy < RE >(CO2) decreases as n increases and converged to the experimental bulk limit rapidly. The normalized recombination energymore » < RE >(CO2) was calculated to be -52.2 kcal/mol for the monomer and -30.7 kcal/mol for n = 16, as compared to the experimental value of -27.9 kcal/mol for the solid phase reaction. Infrared spectra for the lowest energy isomers were calculated, and absorption bands in the previous experimental infrared studies were assigned with our density functional theory predictions. The 13C, 17O, and 25Mg NMR chemical shifts for the clusters were predicted. We found that the results provide insights into the structural and energetic transitions from nanoclusters of (MgCO3)n to the bulk and the spectroscopic properties of clusters for their experimental identification.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). National Center for Computational Sciences
  2. Univ. of Alabama, Tuscaloosa, AL (United States). Dept. of Chemistry
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
OSTI Identifier:
1261428
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Volume: 119; Journal Issue: 14; Journal ID: ISSN 1089-5639
Publisher:
American Chemical Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY