COMPUTATION OF THE LOCAL ELECTRONIC DENSITY OF STATES FOR ALL SURFACE ATOMS IN DIFFERENT MICROFACET MODELS OF TiO_2(100)1x3

Recently microfacets on reconstructed TiO2 (100) 1 x 3 have been observed with atomic res­ olution  by  scanning  tunneling  microscopy  (Murray  el al.  BUM) and  surface core-level-shift photoeleclron diffraction  (Hardman  el  al.  1993).  Determination  of the electronic structure of extended surface defects is a formidable computational problem and only now possible by using the most powerful computers.
Earlier studies, by one of the authors (Michalewicz 1994a, 1994b, Michalewicz and Priebatsch 1995), on the electronic structure of transition metal oxides with high concentration of point defects in a very large atomistic models of up to 500,000 atoms, have now been extended to the very large samples with extended surface defects such as microfacets.
We present computed results for the Local Density of Stales (I, DOS) for up to 13 uiieipiivalent Ti ami O sur­face atoms in the vicinity of a microfacet for live different models of a microfacet. This type of calculation might be useful for extracting information on atomic composition in the spectroscopic mode of operation of the Scanning Tunneling Microscope.
We also present the results of benchmark analysis of our electronic structure code on a vector-parallel comput­ er (Cray C90). We compare vector-parallel performance with the SIMI) performance (MasPar MP-1, MP-2 1BK PE) and report on our efforts to implement the code on MIMD architecture (Cray T3D).