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Origin of the Linear Relationship between CH2/NH/O−SWNT Reaction Energies and Sidewall Curvature: Armchair Nanotubes
journal contribution
posted on 2006-11-29, 00:00 authored by Guishan Zheng, Zhi Wang, Stephan Irle, Keiji MorokumaThe origin of the linear relationship between the reaction energy of the CH2/NH/O exo and endo
additions to armchair (n, n) single-walled carbon nanotubes (SWNTs) and the inverse tube diameter (1/d)
measuring sidewall curvature was elucidated using density functional theory and density functional tight
binding methods for finite-size SWNT models with n = 3, 4, ..., 13. A nearly perfect linear relationship
between ΔE and 1/d all through exohedral (positive curvature) and endohedral (negative curvature) additions
is due to cancellation between the quadratic contributions of the SWNT deformation energy and the
interaction energy (INT) between the deformed SWNT and CH2/NH/O adducts. Energy decomposition
analysis shows that the quadratic contributions in electrostatic, exchange, and orbital terms mostly cancel
each other, making INT weakly quadratic, and that the linear 1/d dependence of INT, and therefore of ΔE,
is a reflection of the 1/d dependence of the back-donative orbital interaction of b1 symmetry from the occupied
CH2/NH/O pπ orbital to the vacant CC π* LUMO of the SWNT. We also discuss the origin of the two
isomers (open and three-membered ring) of the exohedral addition product and explain the behavior of
their associated minima on the C−C potential energy surfaces with changing d.