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

在本计画中，我们从理论上研究了碱金属表面吸附的成键机制与功函数的覆盖度相关性。所采用的模型是一种LCAO模型，其中考虑了原子轨道之间的非正交性和吸附质构型的随机性。非正交性对共价度的估计是必不可少的，无规性对形成覆盖带起着重要作用，也是功函数温度依赖性的主要来源。到目前为止，在大多数理论中，相互作用仅限于静电相互作用，然后变成排斥。然而，从几年前开始，由于LEED和EELS实验，在某些情况下，这种相互作用在更高的覆盖率下变得有吸引力。除了静电相互作用外，我们还考虑了原子间电子转移引起的另一种相互作用，称为“内聚相互作用”。因此，我们得到的结果，有效的相互作用变得有吸引力的覆盖率较高，通过假设合理的参数值。1993年，我们尝试将这些年来建立的模型和方法应用于“双层吸附”问题。所考虑的系统表示为碱金属（类型1）/碱金属（类型2）/金属。北海道大学的一个研究小组对这一问题进行了研究，得到了一些有趣的结果，其中包括一种可能的新催化机理，到目前为止，我们已经建立了所需的公式，并得到了一些初步的计算结果。

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.