6533b82afe1ef96bd128ca9f

RESEARCH PRODUCT

Symmetry and Models of Double-Wall BN and TiO2 Nanotubes with Hexagonal Morphology

subject

description

The line symmetry groups for one-periodic (1D) nanostructures with rotohelical symmetry have been applied for symmetry analysis of double-wall boron nitride and titania nano- tubes (DW BN and TiO2 NTs) formed by rolling up the stoichiometric two-periodic (2D) slabs of hexagonal structure with the same or opposite orientation of translation and chiral vectors. We have considered the two sets of commensurate DW BN and TiO2 NTs with either armchair- or zigzag-type chiralities, i.e., (n1,n1)@(n2,n2 )o r (n1,0)@(n2,0), respectively. To establish theequilibriuminterwalldistancescorrespondingtotheminimaof energy, we have varied chiral indices n1 and n2 of the constituent single-wall (SW) nanotubes. To analyze the structural and elec- tronic properties of hexagonal DW NTs, we have performed ab initio LCAO calculations using the hybrid HartreeFock/KohnSham exchange-correlation functional PBE0 as implemented in CRYSTAL-09 code. The inversely stacked structure of zigzag-type DW BN NT, characterized by arrangement of positively and negatively charged rings in each atomic cross section (consisting of either B or N atoms, respectively), has been found to be energetically more preferable as compared to the straightly stacked structure containing nanotube rings consisting of the same type ofatomsincrosssections,i.e.,B(N)andB(N).Inarmchair-typeDWBNNTs,eachatomicringcontainsthewholenumberofBN bonds,whichreducestheelectrostaticinteractionbetweenbothwalls.Ontheotherhand,maincontributiontointerwallbondingin DW TiO2 NTs is provided by interaction between the nearest oxygen and titanium ions of neighboring shells. The interaction between the walls results in a decrease of band gaps for double-wall NTs as compared to those for SW NTs, which is substantially larger for TiO2.