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 Mg^2- and O² ions, but that a small nonspherical distortion of Mg and O is observable in both experiment and theory. The experimental charge distribution of O² is more diffuse than the theory, which may be due to the breathing effect of O^2- in a vibrating lattice.