THEORETICAL STRUCTURE FACTORS AND ELECTRON-DENSITY OF MAGNESITE (MGCO3)

Theoretical structure factors F-q of rhombohedral magnesite (MgCO3) ha ve been computed by quantum-mechanical periodic Hartree-Fock methods a nd compared with observed \F-o\ (literature data) and conventional F-c (independent-spherical-atom model) values. The corresponding R(oq), R (oc) and R(qc) agreement factors (overall values 2.03, 2.11 and 1.80%, respectively) are analysed versus sin(theta)/lambda, showing the effe cts of chemical bonding and of experimental errors. Difference electro n density maps Delta rho(oq), Delta rho(oc) and Delta rho(qc) have bee n calculated for the CO3 and the C-O-Mg planes. Features of the C-O co valent bonding and oxygen lone pair are compared and discussed.