Electronic structures, vibrational analyses, stabilization energies and amorphicity were analyzed for the most stable configurations of the neutral gas phase clusters of calcium carbonate (CaCO 3 ) n (n = 2-7). Minimum-energy structures were generated through simulated annealing using a mix of molecular dynamics/semiempirical optimization and then full optimization at the ab initio level (RHF/6-31G*). HF-level results are calibrated versus MP2/6-31G* results. Though many clusters are symmetric, the structural arrangements are not crystalline and resemble neither calcite nor aragonite. In general, greater symmetry means a lower stabilization energy. The BSSE-and zero point energy-corrected stabilization energies appear to plateau at about -113 kcal/mol when n = 7. Amorphous clusters start appearing when n = 4 and the lowest-energy minima for n C 5 are of C 1 symmetry. No solvent effect is necessary to induce amorphism.

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