Atom Cluster Model Research Articles

Atomic clusters and cluster models in solid state physics

Since it became possible to study experimentally the evolution of a metal and the transition from atomic and molecular to surface and bulk properties, the study of clusters, especially metal clusters due to their role in heterogeneous catalysis, represents a highly active research area. On the other hand, clusters serve also as very useful models in solid state physics to investigate impurity, surface, and interface problems. Both cluster aspects will be discussed in addition to the role of cluster calculations in aperiodic polymer and band structure computations. We also report results of Li-cluster studies. Correlation effects, calculated with the coupled cluster method, are discussed in connection with the onset of Pierls' distortion in Li-rings. Finally, it is demonstrated how the cluster model is used to investigate polymer-metal surface interactions and how these interactions influence and change the polymer conformation.

Electronics states of a surface nickel atom on the nickel (001) surface

Electronic states of a Ni(001) surface atom, corresponding to different d-occupations, are calculated for a 49 atom cluster model of the surface. SCF and CI calculations on a variety of low lying states are reported. Strong mixing between d 9 and d 10 configurations is found for the lowest states of different symmetries with the splitting between the states ranging from 1.7 to 2.0 eV. In contrast, the d 8 configurations do not interact strongly with other d configurations and lie energetically much higher at ∼3.0 eV. Thus, the splitting between d 9 and d 10 configurations is comparable to that of the isolated atom whereas the d 8 configuration is greatly destabilized. The cluster produces a manifold of closely spaced electronic states above the ground state thus modeling the density of unoccupied states above the Fermi level.

A large unit cell semiempirical molecular orbital approach to the properties of solids. III. Ionic crystals: lithium fluoride and potassium chloride

For pt.II see ibid., vol.12, p.2497 (1979). A large unit cell-complete neglect of differential overlap (LUC-CNDO) method has been used to predict some properties of lithium fluoride and potassium chloride crystals. A 16 atom cell and a parameter set chosen to match the properties of the relevant diatomic molecules form a basis for the calculation. The results are compared with predictions from a 27 atom cluster model, with previous band-structure calculations and with experiment. It is concluded that the approach has great potential for the study of ionic solids with and without defects.

Molecular orbital study of the interaction of carbon monoxide and carbon dioxide with copper (100)

A molecular orbital study is made of the structures and energy levels of CO and CO 2 on Cu(100). The importance of self-consistency is discussed. CO is found to occupy fourfold indentations, in agreement with the semiempirical results of Doyden and Ertl. The C-surface distance is 1.0 Å and the CO bond stretches less than 0.1 Å. Large models of the surface show convergence of the electronic structure with four CO molecules on a twelve Cu atom cluster model of the surface. At coverages up to c(2 × 2) half monolayer, calculated energy levels match Demuth and Eastman's phase I photoemission spectrum. Phase II, as observed by them, has no analog in the calculations. No evidence is found for CO deviating from perpendicular to the surface when tightly bound. CO 2 is found to adsorb more weakly to the surface. This molecule rests in a μ bridging position, bonded through mixing of Cu d with CO 2 π ∗ orbitals. It bends, with an angle of 120°, which is significantly similar to 122° for the 1B 2 excited state of free CO 2, which has an electron promoted to the π ∗ orbital. On the basis of this molecular orbital study, extrapolations to Ni and Zn surfaces and OCS, CS 2, CSe 2 and CTe 2 are made.