Charge Density of MgO: Implications of Precise New Measurements for Theory

A tenfold improvement in the accuracy of measured low-order structure factors for MgO has been achieved using the convergent beam electron diffraction technique. These results allow a meaningful comparison to be made with the latest calculations. We find that the MgO charge density can be described by a superposition of spherical ${\mathrm{Mg}}^{2+}$ and ${\mathrm{O}}^{2-}$ ions, but that a small nonspherical distortion of Mg and O is observable in both experiment and theory. The experimental charge distribution of ${\mathrm{O}}^{2-}$ is more diffuse than the theory, which may be due to the breathing effect of ${\mathrm{O}}^{2-}$ in a vibrating lattice.