Papers by Keyword: Shear Modulus (G)

Abstract: The structural, elastic and optical properties of Ag-doped rutile TiO2 are studied using the first principles calculations method. Four different functionals are employed using the ultrasoft pseudopotentials (USPs) on a supercell of size 2a × 2b × 1c. The band gaps of un-doped TiO2 obtained using PBE, RPBE, PW91 and LDA-CA-PZ are 1.861, 1.873, 1.857 and 1.854 eVs respectively. However, after Ag substitution in the supercell, the band gaps are reduced for all of the functionals. After substitution, in the region near to the Fermi level, some new electronic states are observed. The calculated elastic constants show that the structure is mechanically stable. The obtained values of the B, G and elastic constants of un-doped TiO2 are consistent with prior published experimental findings. For Ag-doped supercell, implementing PW91, B and G are 119 and 62 GPa. For the same size of supercell, using LDA-CA-PZ, B and G are 152 and 70 GPa. Besides, the results of the optical properties show that the major absorption peaks for all of the functionals locate away from the visible region. This shows poor absorption of visible light and weak photocatalytic activity of rutile TiO2.

Abstract: Soon after the discovery of carbon nanotubes, it was realized that the theoretically predicted mechanical properties of these interesting structures could make them ideal for a wealth of technological applications. A number of computer simulation methods applied to their modeling, has led over the past decade to an improved but by no means complete understanding of the mechanics of carbon nanotubes. Tersoff potential has been widely used but it has since been modified many times. The latest is the second-generation reactive empirical bond order potential by Brenner and co workers, which is being used in this work for manipulating these tiny structures. We outline the computational approaches that have been taken. The elastic moduli of armchair, zigzag and chiral nanotubes have been computed. We generate the coordinates of carbon nanotubes of different chirality’s and size. Each and every structure thus generated is allowed to relax till we obtain minima of energy. We then apply the requisite compressions, elongations and twists to the structures and compute the elastic moduli. Young’s modulus is found to be dependent on tube radius for thinner tubes and attains a constant value of the order 1TPa. Our results of Poisson’s ratio and shear modulus are also encouraging and compare well with other theoretical and experimental work.