A charge density study of MgCu2 and MgZn2 by the maximum entropy method

The charge density distributions of the Mg-base Laves phase MgCu2 and MgZn2 were obtained from the synchrotron powder diffraction data by the Maximum Entropy Method (MEM). In the MEM charge density, the overlapped electron densities were found between Cu-Cu atoms in the case of MgCu2 and between Zn-Zn atoms. These covalent bonds form the electronic kagome network for the both compounds. By the geometrical consideration, this characteristic feature can be interpreted as the existence of p(3)d(3) hybridization of the Cu and Zn atoms. On the other hand, there were no such overlapped densities around Mg atoms, which denies any significant covalency between Mg and Cu or between Mg and Zn atoms. Furthermore, the peculiar distortion of the covalent bond network is found in the obtained MEM charge densities for the both compounds, that is, the covalent bonds are shifted towards the Mg atoms. This rather unusual bond nature should be due to the ionic interaction between the hybridized orbital and positively charged Mg ions. As for the MgZn2, the difference of the hybridized electron density was found related to the zigzag pattern of hexagonal stacking sequence.