AB Initio Calculations on Work Functions of Cathode Surfaces with Adsorbed Atoms

Summary form only given. We study the work functions of cathode surfaces with adsorbed atoms by using ab initio calculations. We used the standard slab geometry to model the surface systems. The tungsten (W) substrates are modeled by 5-layer slabs for the W (001) orientations. This provides one surface as well as bulk regions in all of the slab, which approximate the atomic structure encountered in real materials. The overlayers are pseudomorphic and are put on the top side of the substrate W slab. The material systems above the substrate in the supercell consist of a slab with 1 or 2 atomic layers of adsorbates, such as hydrogen, oxygen, nitrogen, or others. The electronic properties of barium absorbed or coated onto a W (001) surface are also investigated. For this case, three fixed tungsten layers are used to approximate the real bulk material. In order to present the characteristic of tungsten surface, we put another two tungsten layers and 1 or 2 atomic layers of barium on the bulk in sequence. A preliminary ab initio calculation shows that the work function of the tungsten substrate estimated to be 4.587 eV could be lowered by approximately 1 to 2 eV due to the adsorbed atoms distributed onto a W(001) surface. Detail analysis and numerical results of variant material systems will be presented.