Methods
All calculations such as geometry optimizations and solvent effects have
performed using GAMESS program.41,42 For these
calculations, density functional theory (DFT) with ONIOM
(ωB97X-D/aug-cc-pvdz and ωB97X-D/3-21G) level of theories have been
employed.43 The optimizations of all structures were
performed without symmetry constraint or pre-defined conformational
structures. The absence of imaginary frequency verified that a structure
was a true least at its respective level of theory. The results of
frequency calculations were used after applying appropriate scaling
factor.44 The effects of solvent were studied through
SCRF keyword using Tomasi’s polarized continuum (PCM)
model.45 Three solvents, two polar (water with
ε=78.355 and acetone with ε=20.493) and one nonpolar (cyclohexane with
ε=2.017), were selected to study of the solvent effect on the adsorption
energies. These values in both gas and solvent phase obtained from the
Gibbs free energies (ΔGad) that were calculated for CNT and DNTs
according to equation 1.
∆Gad=GCNT-CO −
(GCNT+GCO) (1)
NBO calculations of all structures were performed using the
NBO.46 Also, QTAIM analyses were employed using the
AIMAll 15.09.27 program.47 Density of state (DOS)
plots were obtained from the GaussSumm 2.2.1
program.48