CRITICAL-POINTS IN A CRYSTAL AND PROCRYSTAL

The critical points in the model electron density distributions of LIF , NaF, NaCl, and MgO crystals, constructed from accurate X-ray diffrac tion data, are determined. For LiF and MgO they are compared with thos e obtained from a Hartree-Fock electron density calculation. Both expe riment and theory show the same type of critical points on the bond li nes. The topological features in areas between structural units, where the electron density is low and near-uniform, turn out to be model de pendent and cannot be established well with the data available. Topolo gical analysis of procrystals (hypothetical systems consisting of sphe rical atoms or ions placed on the same sites as atoms in real crystal) show that (3, -1)critical points, usually connected with bonding inte raction, are observed on interatomic lines in these nonbonded systems as well.