First principles total energy calculations were performed in order to determine oxygen vacancy migration energies in Ta2O5 . A simplified version of the crystalline orthorhombic phase of Ta2O5 was used in this study. O vacancies in the chosen model of Ta2O5 can be broadly classified into ‘cap’ and ‘in-plane’ sites based on their location in the lattice. The cap type of vacancies display the lar...

Spin-polarized density functional theory has been used to study the properties of vacancies in a graphene sheet and in single-walled carbon nanotubes (SWNTs). For graphene, we find that the vacancies are magnetic and the symmetry of the sheet is broken by the distortion of an atom next to the vacancy site. We also studied vacancies in four armchair SWNTs from (3,3) to (6,6) and six zigzag SWNTs...

We investigate the effect of cell-size on the energetics of vacancies in Aluminum using orbital-free density functional theory with non-local kinetic energy functionals. Extending the recently developed coarse-graining techniques based on quasi-continuum reduction to include non-local kinetic energy functionals, we consider cell-sizes up to a million atoms in this study. We find remarkable cell...

The stability and reactivity of the hematite, Fe2O3(0001) surface are studied by density functional theory including an on-site Coulomb term (DFT+U). Even under oxygen rich conditions, the metal-terminated surface is shown to be stable. On this surface termination, the isolated water molecule forms a heterolytically dissociated structure with the OH- group attached to a surface Fe3+ ion and the...

Electron localization and polaron mobility in oxygen-deficient as well as Li-doped monoclinic tungsten trioxide have been studied in the adiabatic limit in the framework of density functional theory. We show that small polarons formed in the presence of oxygen vacancy prefer the bipolaronic W5+-W5+ configuration, whereas the W6+-W4+ configuration is found to be metastable. Our calculations sugg...

Hexagonal boron nitride (h-BN) is an electrical insulator with a large band gap of 5 eV and a good thermal conductor of which melting point reaches about 3000 °C. Due to these properties, much attention was given to the thermal stability rather than the electrical properties of h-BN experimentally and theoretically. In this study, we report calculations that the electronic structure of monolaye...

Abstract In this study, radiation-induced precipitation of transmutation products is addressed via the development a new solute and vacancy concentration dependant Ising model for W–Re–Os system. This includes interactions between both Os Re atoms with vacancies, thus facilitating more representative simulations in fusion reactor components. Local dependencies are introduced W–Re, W–Os Re–Os pa...

We present calculations of the bound state energy levels of anion vacancies near the surface of a III-V semiconductor. We consider the (110) surface of GaAs, InP, and the Ga1_xAlxAs alloy system. As the vacancy is moved toward the surface, the energy levels are only slightly perturbed until the vacancy reaches the second atomic layer from the surface. At this point, the anion vacancy levels mov...

The SIESTA suite of programs allows periodic density functional theory calculations to be carried out on system sizes of several hundred atoms. Here we make use of this to study the interface between Au and MgO surfaces. Atomic Au on MgO(100) shows preferential binding over surface anion sites, while the binding energy at a surface anion vacancy is significantly higher than on the stoichiometri...