Abstract
A theoretical study of imogolite-like single wall nanotubes as a function of silicon and germanium content and their tubular radius is presented along with mapping of silicon-germanium content properties in models that contain from 9 gibbsite-like units to 13 gibbsite-like units with a silicon-germanium content of 0, 0.20, 0.40, 0.60, 0.80, and 1.00. The imogolite nanotubes were built setting periodic boundary conditions to density functional theory (DFT) geometry-optimized models along both radial and axial directions in order to obtain the stable structure. The DFT calculations were carried out on the point and for various points, using the GGA-PW91 functional, finding an optimal unit cell length of 8.72 and using a double numeric (DN) and double numeric with polarization (DNP) basis set, respectively, along the axial direction. The structural properties were analyzed through the evolution of the x-ray diffraction pattern as a function of both and . A linear correlation between the tube radius and the position of the first two peaks on the x-ray diffraction is found. The imogolite surface charge was mapped with the Hirshfeld charge showing the characteristic acid tendency experimentally reported. The reactivity of imogolite-like structures was studied employing the total density of states and the band gap evolution as a function of and showing an increasing behavior with . The local reactivity was analyzed by looking at the local density of states in models with and 1.0 with . Finally, the frequency analysis was carried out in the optimized structure on the point finding a good agreement in the vibrations with those reported in the literature.
8 More- Received 2 May 2007
DOI:https://doi.org/10.1103/PhysRevB.76.125421
©2007 American Physical Society