Lattice energies of calcite-structure metal carbonates I. Calculation of carbonate ion charge distributions from oxygen polarizabilities

Abstract

Carbonate ion charge distributions of five calcite-structure metal carbonates (i.e., CaCO 3(s), CdCO 3(s), FeCO 3(s), MgCO 3(s), and MnCO 3(s)) have been calculated by a two-step process. First, electronic polarizabilities for oxygen in the above-mentioned metal carbonates were determined from experimental crystal refractivity data by employing the Lorentz local field method (Lawless, W. N. and DeVries, R. C., J. Phys. Chem. Solids, 1964, 25, 1119) in the point dipole approximation. By varying the size of the spherical Lorentz cavity, convergence of the calculated components (parallel and perpendicular) of the oxygen atom polarizability was observed to occur at a radius of approximately 65 Å. Metal ion polarizability data was obtained from Tessman et al. [2] (Tessman, J.R., Kahn, A. H. and Shockley, W., Phys. Rev. 1953, 92, 890) while the carbon atom polarizability was ignored. With these oxygen polarizabilities at hand, the second phase of the approach used Gaussian '94 (Revision C.3, Frisch,M. J. et al., Gaussian, Inc., Pittsburgh, PA, 1995) as a tool for performing polarizability calculations on CO 2 2− as a function of the partial charge on oxygen ( Q oxy). By approximating the polarizability of CO 3 2− as three times the oxygen atom polarizability ( α oxy), a correlation between α oxy and Q oxy was obtained. Upon comparing this relationship to the oxygen polarizabilities found via the Lorentz local field method, Q oxy values were predicted for all five metal carbonates.