THEORETICAL STUDY ON CONVERAGE DEPENDENCE OF BONDINGMECHANISM AND WORKFUNCTION ALKALIMETAL / METAL SURFACE

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In this project, we have theretically investigated the coverage dependence of the bonding mechanism and the workfunction for alkali-atom adsorbed metal surface. The employed model is a type of the LCAO model in which the nonorthogonality between atomic orbitals and the randomness of the adsorbate configuration are taken into consideration. The nonorthogonality is essential to estimate the degree of covalency and it has been shown that the randomness plays an essential role on forming of the overlayr band and is a dominant origin of the temperture dependence of the workfunction.In 1992-1993, we investigated the coverage dependence of effective interactions between adatoms. In most theories, so far, the interaction is confined to the electorstatic one and then becomes repulsive. Since several years ago, however, it is suggested due to the LEED and EELS experiments that the interaction becomes attractive at higher coverages in some case. we have taken another interaction caused from the electron transfer between the adoatoms, which is called 'cohesive interaction', besides the electrostatic interaction. As a consequence, we obtained the result that the effective interaction becomes attractive at higher coverage by assuming reasonable values of parameters. (published in Phys.Rev.B)In 1993, we have try to investigate apply tha present model and method established for these years to the problem of 'two-layr adsorption'. The system considered denoted as alkali-metal(type 1 )/alkali-metal(type 2)/metal. A research group in Hookaido University have investigated this subject and obtained some interesting results including a possible new catalysis mechanism.Up to the present time, we have constructed the requisite formulation and obtained some preliminary calculated results.