STATIC LATTICE AND ELECTRON PROPERTIES OF MGCO3 (MAGNESITE) CALCULATED BY ABINITIO PERIODIC HARTREE-FOCK METHODS

Calculations of the Hartree-Fock ground-state wave function and total energy of crystalline MgCO3 have been performed using the ab initio CRYSTAL program. Contracted Gaussian-type functions have been used to represent 18, 18, and 14 (including d) atomic orbitals for Mg, O, and C, respectively. The rhombohedral calcite-type structure has been fully relaxed, determining the equilibrium lattice constants and coordinate of the 0 atom as a function of volume. The bulk elastic modulus and the C33 and C-11 + C-12 elastic constants have been calculated. Deviations from experimental data are within 1% for the structural parameters and amount to + 6.8% for the bulk modulus. The computed binding energy (including a correction for the electron correlation based on local-density-functional theory) is smaller by 6% than the measured value. Mulliken electron charges are + 1.750, - 0.986, and + 1.207 Absolute value of e for Mg, 0, and C. Energy bands, density of states, and electron-density maps permit the characterization of chemical bonding within the CO3 molecular unit and between CO3 groups and Mg atoms.