N-doped SWCNT with different concentration of doped nitrogen atoms were investigated through density functional theory (DFT) calculations for detecting CO molecule. The CO molecule was adsorbed to different sites of the modified nanotubes and their geometric structures and electronic properties were investigated after full optimization. A significant change can be observed in adsorption energies and electronic properties of N-doped SWCNT after CO adsorption. By increasing the number of nitrogen atoms in each unit cell, these properties change more obviously. So these modified nanotubes can be used as CO sensors.
The structural and electronic properties of polyaniline, polypyrrole, and poly(aniline-co-pyrrole) (Ani-co-Py) in periodic form were investigated using calculations based on density functional theory (DFT). One to three monomers of aniline and pyrrole were placed in a supercell, and the effects of dihedral angles between the monomers on the electronic properties of the polymers were explored. All polymer configurations were optimized, and the band structures and densities of states (DOSs) were calculated and compared. The band gap of each polymer was calculated as the smallest energy difference between the HOMO and LUMO bands. The results showed that both sets of homopolymers exhibit semiconducting behavior which becomes less prominent after copolymerization. A comparison of the band structures of the homopolymers and the copolymer indicated that the pyrrole in the copolymer acts as an acceptor. The projected density of states (PDOS) was examined to obtain additional insight into orbital interactions and to identify the atoms that are most influential in the electronic properties of the studied polymers.
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