Imogolite-like nanotubes: structure, stability, electronic and mechanical properties of the phosphorous and arsenic derivativesElectronic supplementary information (ESI) available: Graphics of strain energy of armchair NTs, total and partial density of states (DOS) for the most stable structures, electrostatic field of the most stable zigzag and armchair NTs, complete tables for all studied NTs, X-ray powder diffraction simulations and BOMD/SCC-DFTB calculations. See DOI: 10.1039/c3cp44250k

Imogolite is a single-walled aluminosilicate nanotube (NT) found in nature that can be easily synthesized, as well as its analogue aluminogermanate NT. Based on geometrical assumptions and pKa values, species such as H 3 PO 4 , H 3 PO 3 , H 3 AsO 3 , H 3 AsO 4 could also be candidates to form imogolite-like structures. In the present work, we provide insights about the stability, electronic, structural and mechanical properties of possible imogolite like NTs by means of self-consistent charge density-functional tight-binding method (SCC-DFTB). Similarly to aluminogermanate, where the tetrahedral silicate groups are replaced by germanate, in this work tetrahedral silicate groups are substituted by phosphate, phosphite, arsenate and arsenite units in the imogolite structure. Detailed analysis is focused on structural properties, strain energy, band gap and Mulliken charges distribution. The calculated strain energy curves for all studied zigzag imogolite-like NTs present well-defined minima, which change as a consequence of composition variation. Moreover, the strain energy curves of armchair imogolite-like NTs also present minima, although in all cases less stable than zigzags by at least 2.2 meV per atom. The insulating NT behaviour changes after internal modification from silicate to phosphate, phosphite, arsenate and arsenite, as well as the charge distribution inside and outside the nanotubes. We provide insights about the stability, electronic, structural and mechanical properties of possible imogolite like NTs by means of self-consistent charge density-functional tight-binding method.