3.3. QTAIM Analyses
Quantum theory of atoms in molecule (QTAIM) analyses is the most valuable ways to calculate intermolecular interactions and consider the nature of interactions between CO molecule and CNT or DNTs. The electron density (ρ ) and Laplacians of electron densities (2ρ ) at the bond critical points (BCP) for all structures are shown in Table 3. The values of2ρ are in the ranges of 1.84×10-2 to 3.10×10-1e/a05 for CNTs, 4.21×10-2 to 1.39×10-1e/a05 for SCNTs, 8.76×10-2 to 5.92×10-1e/a05 for NCNTs and 1.76×10-2 to 2.39×10-2e/a05 for BCNTs. In this regard, the positive values of ∇2ρ (at critical points) indicate that the nature of these interactions is non-covalent. Based on the values of electron densities, the orders of2ρ are the same as stabilities and the values of 2ρ increased through increasing the stability of complexes.