Theoretical structure factors and electron density of magnesite (MgCO3)

Theoretical structure factors Fq of rhombohedral magnesite (MgCO3) have been computed by quantum-mechanical periodic Hartree-Fock methods and compared with observed |Fo| (literature data) and conventional Fc (independent-spherical-atom model) values. The corresponding Roq, Roc and Rqc agreement factors (overall values 2.03, 2.11 and 1.80%, respectively) are analysed versus sin(θ)/λ, showing the effects of chemical bonding and of experimental errors. Difference electron density maps Δρoq, ΔρOC and Δρqc have been calculated for the CO3 and the C - O - Mg planes. Features of the C - O covalent bonding and oxygen lone pair are compared and discussed.