Corrected effective medium method. 3. Application to clusters of magnesium and copper

Abstract

The authors present a number of new concepts in the recently developed corrected effective medium (CEM) theory. First, the general CEM theory is specialized to the case of an infinite periodic three-dimensional solid. Second, construction of a covalent embedding function of the electron density from diatomic and bulk binding potentials is detailed. On the basis of the smoothness of the function in interpolation between the (low density) diatomic and (high density) bulk limits, we argue that this function is dependent only on the types of atoms in a system and not on the number of atoms in the system (i.e., a universal function of the electron density for particular types of atoms). Applications are made to the description of the structures and energies of homogeneous metal clusters containing from 2 to 201 atoms. Predictions of the equilibrium structures and energies of various high-symmetry structures of Mg{sub 3}, Mg{sub 4}, Cu{sub 3}, Cu{sub 4}, Cu{sub 5}, Cu{sub 13}, and Cu{sub 79} are compared to a number of ab initio and SCF-LSD results. The agreement is quite good even for the small clusters and becomes essentially perfect by Cu{sub 13}. Selected two-dimensional distortions of four-, five-, and seven-atom clusters are considered inmore » detail, with the energetics presented via contour plots. These enable the determination of barriers to isomerization and/or the existence of especially floppy modes of the metal cluster. Geometrical optimization is performed for various configurations of Mg{sub 3-6}, Cu{sub 3-14}, and Cu{sub 19}. These accurate calculations on this range of clusters enable us to investigate the structural stability of the larger metal clusters for the first time. For still larger clusters of up to 201 atoms, we present binding energies for spherical bulk fragments to determine the onset of bulk binding.« less