Papers by Keyword: Density Functional Calculation

Abstract: We present the results from first principle calculations of H₂O adsorption on oxygen-covered Fe (100) surface. The calculations are based on a density-functional theory, surface modeling which uses supercell slab models. As a surface oxygen coverage increases, the surface is not activated, which makes the adsorption of water molecules on Fe surface unfavorable. It has been found that the surface covered oxygen exerts an influence on the adsorption of H₂O molecule on Fe surface.

Abstract: The geometric and electronic structures of Cr chains are studied by the first-principles of density-functional method. The present calculation results show that chromium can form planar chains in linear, zigzag, dimer, and ladder form one-dimensional structures. The most stable geometry chain among the studied structures is the ladder-form chain with five nearest neighbors. The dimer structure is found to be more stable than the zigzag one. Further more, the relative structural stability, the electronic energy bands, the density of states is discussed based on the ab initio calculations.

Abstract: We describe a comprehensive ab initio investigation of phase stability and mechanical properties of W-Ta and W-V alloys, which are candidate materials for fusion power plant applications. The ab initio density functional calculations compare enthalpies of mixing for alternative ordered atomic structures of the alloys, corresponding to the same chemical composition. Combining the ab initio data with large-scale lattice Monte-Carlo simulations, we predict several low-energy intermetallic compounds that are expected to dominate alloy microstructures, and hence the low-temperature phase diagrams, for both alloys. Using the predicted ground-state atomic alloy configurations, we investigate the short-range order, point defect (vacancy and self-interstitial atoms) energies, and thermodynamic and mechanical properties of W alloys as functions of their chemical composition. In particular, we evaluate the anisotropic Young modulus for W-Ta and W-V alloys from ab initio elastic constant calculations, with the objective of comparing the predicted values with experimental micro-cantilever measurements. Also, using the calculated Poisson ratios for binary W alloys, which combine tungsten with more than 40 different alloying elements, we investigate if alloying improves the ductility of tungsten-based materials.

Abstract: The behavior of water molecules with sulfate on the Fe(001) surface has been investigated using a first-principles method based on density-functional theory (DFT) with numerical atomic orbitals as basis functions for the description of valence electrons and nonlocal pseudopotentials for the atomic core. We present results for the adsorption structure and the bonding nature as caused by the adsorption-induced variations in the electron density and the projected density of states. We have found that the structure of absorbed sulfate depends on the coverage of water molecule on the surface. Analysis of electrostatic potential at an aqueous metal interface provides an appropriate framework to understand complicated potential structures. The mechanism of proton transfer through dissociative adsorption and hydrogen bonding of water molecules has been obtained from calculated results.

Abstract: We employ density functional calculations to investigate the doped Al/TiC interfaces. The effects of different segregation atoms are discussed. The results show that the different transition metal atoms have different effects on the adhesion. Results of analysis of atom size and electronic structure have shown that both atom size and activity of the doped atom influence on the adhesion. Our results are consistent with other results of doped metal-oxide interface.