Using first-principles calculations, we systematically study the dissociations of O2 molecules on different ultrathin Pb(111) films. According to our previous work revealing the molecular adsorption precursor states for O2, we further explore why there are two nearly degenerate adsorption states on Pb(111) ultrathin films, but no precursor adsorption states existing at all on Mg(0001) and Al(111) surfaces. The reason is concluded to be the different surface electronic structures. For the O2 dissociation, we consider both the reaction channels from gas-like and molecularly adsorbed O2 molecules. We find that the energy barrier for O2 dissociation from the molecular adsorption precursor states is always smaller than that from O2 gas. The most energetically favorable dissociation process is found to be the same on different Pb(111) films, and the energy barriers are found to be influenced by the quantum size effects of Pb(111) films.
By performing density functional theory plus U calculations, we systematically study the structural, electronic, and magnetic properties of UO2 under uniaxial tensile strain. The results show that the ideal tensile strengths along the [100], [110], and [111] directions are 93.6, 27.7, and 16.4 GPa at strains of 0.44, 0.24, and 0.16, respectively. After electronic-structure investigation for tensile stain along the [001] direction, we find that the strong mixed ionic/covalent character of U-O bond is weakened by the tensile strain and there will occur an insulator to metal transition at strain over 0.30.
We have carried out first-principle calculations of Mg adsorption on Si(111) surfaces. Different adsorption sites and coverage effects have been considered. We found that the threefold hollow adsorption is energy-favoured in each coverage considered, while for the clean Si(111) surface of metallic feature, we found that 0.25 and 0.5 ML Mg adsorption leads to a semiconducting surface. The results for the electronic behaviour suggest a polarized covalent bonding between the Mg adatom and Si(111) surface.
Local structural changes from liquid to amorphous state in three Cu45Zr55-xAlx (x=3, 7, 12) ternary metallic glasses have been investigated by the ab initio molecular dynamics simulation. The atomic structure of the glasses has been analyzed by means of bond-type index method in Honeycutt-Andersen and Voronoi tessellation method. Al-centered icosahedral clusters are identified as the basic local structural units and these Al-centered stable clusters play a key role in the structural heterogeneity and glass-forming ability of the Cu-Zr-Al bulk metallic glasses.
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