Ming-Qiu Tan

A Possible New Parent Compound Sr4Al2O6Fe2As2 with High-TC Superconductivity

Inspired by the experiments of (Sr 2 VO 3 ) 2 Fe 2 As 2 and (Ca 4 Al 2 O 6- x )(Fe 2 As 2 ), the density-functional theory calculations are carried out to predict a possible parent compound (Sr 4 Al 2 O 6 )(Fe 2 As 2 ) for iron-based superconductors. The magnetic orders of Fe atoms are easy to adopt striped anti-ferromagnetic (S-AFM) order for its ground state. The longest d FeAs and the angle (Fe–As–Fe) most close to 109.47° are forecasted compared with (Sr 2 VO 3 ) 2 Fe 2 As 2 and (Ca 4 Al 2 O 6- x )(Fe 2 As 2 ) for the nonmagnetic (NM) configuration, which may imply that (Sr 4 Al 2 O 6 )(Fe 2 As 2 ) is a potential parent compound of high- T C superconductors. The densities of states around the Fermi energy ( E F ) mainly come from the Fe-3d orbital for both NM and S-AFM configurations. The band structure computation shows that this compound is anisotropic and the Fermi surface sheets of (Sr 4 Al 2 O 6 )(Fe 2 As 2 ) are similar to (Ca 4 Al 2 O 6 )(Fe 2 As 2 ) for the NM configuration. The result will be...

Initial Subsurface Incorporation of Oxygen into Ru(0001): A Density Functional Theory Study

The adsorption and diffusion of oxygen on Ru(0001) surfaces as a function of coverage are systematically investigated by using density functional theory. A high incorporation barrier of low-coverage adsorbed oxygen into the subsurface is discovered. Calculations show that the adsorption of additional on-surface oxygen can lower the penetration barrier dramatically. The minimum penetration barrier obtained is 1.81 eV for a path starting with oxygen in mixed on-surface hcp and fcc sites at an oxygen coverage of 0.75 ML, which should be regarded as close to 1 ML. Energy diagrams show that oxygen-diffusion barriers on the surface and in the subsurface are much lower than the penetration barrier. Oxygen diffusion on the surface is an indispensable step for its initial incorporation into the subsurface.

Nitric Oxide Adsorption and Dissociation on Nb(100) Surface

We have studied nitric oxide (NO) adsorption and dissociation on the Nb(100) surface by using the density-functional theory and total-energy calculations. On the Nb(100) surface, at high coverage the tilted NO prefers to adsorb on hollow sites as the most stable adsorption configuration, while at lower coverage the tilted bridge site is the most favorable site. For vertical NO adsorption, similar structural features on top and bridge sites are found in different coverage. Moreover, NO molecules adsorbed on hollow sites of c(2×2) and p(2×2) cells are easy to dissociate to forming the atomic adsorption states from PES calculations. The further analysis based on electronic states reveal that the essential interaction between NO and metal substrate is the hybridization of NO 2π * -orbital and the d-bands of surface niobium atoms. For the tilted NO adsorption, NO 1π and 5σ states are superposed, which are hybridized with niobium d orbitals strongly.