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In this study, we conduct calculations of Ag- and Sr-doped in 3C-SiC using density-functional. To model defective systems, we dope Ag and Sr atoms in substitutional and interstitial sites. We use a supercell model consisting of 64 atoms and relax all atoms so that the atomic forces are less than $5.0\times 10^{-3}$eV/Å. Then, we calculate the defect formation energies for each system. The calculated defect formation energies are 5.67eV and 7.77eV for substitutional Ag and Sr, respectively. In the case of the interstitial sites, the lowest defect formation energies are 10.36eV (Ag) and 14.63eV (Sr). We conclude that Ag and Sr are energetically favorable to be trapped at the substitutional site. Furthermore, the substitutional configuration of Ag is more stable than that of Sr. We check the converged value of the defect formation energies using a 216-site supercell and find that the energy difference is only 0.21eV. Thus, the 64-atom supercell is reliable for the calculations.

The chemisorption of one monolayer H atoms on Si(111) surface is studied by using the self-consistent, tight-binding, linear muffin-tin orbital method. Energies of adsorption systems, the layer projected density of states (LPDOS) and charge distributions are calculated. It is found that the adsorbed H atoms are more favorable on the top site with a distance of 0.185 nm above the Si surface. The LPDOS in the clean surface decreases significantly after H adsorption, since the dangling bonds of the surface atoms are partially saturated by the adsorbed H atoms.

Using the self-consistent tight-binding linear muffin-tin orbital method, we have investigated the electronic structure and adsorption properties of one monolayer Au atoms on a Si(111) surface. The total energies, the layer projected density of states and the charge distributions are calculated in detail. Our calculations show that the most stable position is on the interstitial center site above the Si(111) surface for the adsorbed Au atoms. It is possible for the Au atoms to sit below the Si surface, resulting in a Au–Si mixed layer at the Au/Si interface, which is in good agreement with the experimental results.

The authors draw from half a century of meteorological research to expose flaws in a recent proposal to build 300-m-tall tornado-prevention walls across the U.S. Great Plains. The idea behind the walls is that they would prevent cold and warm air masses from clashing and would therefore suppress tornadoes. The problem with this proposal, however, is that atmospheric fronts ("airmass clashes") are neither a necessary nor a sufficient condition for tornadoes and that the proposed walls would not prevent the formation of fronts in the first place. Additional misconceptions about supercells thunderstorms and tornado formation also are identified.

The reduction of the periodicity of phononic crystals (PnCs) usually leads to the decrease of band gap (BG) width. However, a systematic study of the relationship between the unit cell and the supercell in the proposed hybrid stepped PnCs shows that the BG width can be increased in special cases. How the periodicity of PnCs affects the final BG characteristics is important for the design of PnCs with high structural performance. Supercell of PnCs with imperfections from the rotation of the unit cell was used to demonstrate the relationship between the unit cell and the supercell, which was further used for the wave attenuations of the proposed hybrid stepped PnCs. The rotation angle and the number of the rotating scatterers can be controlled for better structural performance for the PnCs. The different changes of the equivalent stiffness corresponding to the starting and the end frequencies lead to the increase of the BG width when the ration angle of the unit cell is $35^{\circ }$ in the supercell composed of zigzag scatterers and cross scatterers. The rotation of the unit cell in the supercell leads to the decrease of the starting frequency.

Magnetic properties of Ag₂S doped with 3d-transition metals were studied using density functional theory (DFT). It was found that magnetic elements such as Co, Cr and Mn cause magnetism in the structure. The nature of this magnetism is mainly from the 3d-states of the magnetic elements. The magnetic moment of supercells containing various concentrations (x= 2.08%, 4.1%, 8.3%) of dopant atoms has been studied. It was determined that the contribution of the magnetic elements is significant in the total magnetic moment of supercells. Calculation results reveal that when doped with impurity atoms, supercells show half metallicity and ferromagnetic (FM) nature which makes them the best candidate to be used in the field of spintronics.