X-RAY AND ELECTRON-DIFFRACTION STUDY OF MGO

Precise X-ray and high-energy transmission electron diffraction method s were used for the study of electron density and electrostatic potent ial in MgO crystals. The structure amplitudes were determined and thei r accuracy estimated using ab initio Hartree-Fock structure amplitudes as criteria. The electrostatic potential distributions, reconstructed using Fourier series from both X-ray and electron diffraction data, a re in satisfactory mutual agreement and are similar to the theory. The y, however, suffer from restricted experimental resolution and, theref ore, the reconstruction of the electrostatic potential via an analytic al structural model is preferable. The kappa model of electron density was adjusted to X-ray experimental structure amplitudes and those cal culated by the Hartree-Fock method. The electrostatic potential, defor mation electron density and the Laplacian of the electron density were calculated with this model. The critical points in both experimental and theoretical model electron densities were found and compared with those for procrystals from spherical atoms and ions. A disagreement co ncerning the type of critical point at (1/4, 1/4, 0) in the area of lo w, near-uniform electron density is observed. It is noted that topolog ical analysis of the electron density in crystals can be related with a close-packing concept.