Structures and Energetics of (MgCO₃ )_n Clusters ( n ≤ 16)

Journal Article · Fri Mar 13 00:00:00 EDT 2015 · Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

DOI:https://doi.org/10.1021/jp511823k· OSTI ID:1261428

Chen, Mingyang ^[1]; Jackson, Virgil E. ^[2]; Felmy, Andrew R. ^[3]; Dixon, David A. ^[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)

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 CO₃^2-, 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 energy < 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.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1261428
• Journal Information: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Vol. 119, Issue 14; ISSN 1089-5639
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY