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Binding capabilities of hydrogen molecules on Li doped metal carbide nanotubes (MCNT, M = Si, Ge, Sn) have been compared from ab initio-based calculations using quantum mechanical /molecular mechanics methodology. Geometry optimizations are carried out at the ONIOM2 (B3LYP/6-31 + G(d)//LANL2DZ:UFF) level of theory with coronene ring as a model in the high layer. Lithium binding energies on each of the pure armchair (5,5) and zigzag (6,0) MCNTs are calculated. Adsorptions of one and two H2 molecules on the Li doped nanotubes are successively studied. In both cases the complexes are found to be stable and the average adsorption energy falls in between −18 and −38 kcal/mol. Stabilities of Li@MCNT, H2/Li@MCNT, and (H2)2/Li@MCNT systems are confirmed from the HOMO-LUMO gap and three chemical reactivity descriptors such as chemical potential, hardness and electrophilicity index. The charge polarization mechanism plays a pivotal role in the H2 adsorption on the surface of Li@MCNT. The dispersion corrected M06-2X functional is also included in the calculation to investigate the changes in the H2 binding properties. The interaction of H2 with the lithium doped MCNT has also been analyzed from the total electron density maps and density of states projected to different atoms. [ABSTRACT FROM AUTHOR]

Adsorptions of small toxic molecules such as CO, N2, HCN, SO2, H2CO, and NH3 on a single-walled (6,0) SnC nanotube (SnCNT) are investigated using Quantum Mechanics/Molecular Mechanics (QM/MM) methodology. The calculations are carried out at the B3LYP/6-311++G(d,p)//LANL2DZ:UFF level of theory. The high layer of the model consists of a pyrene-type ring on the nanotube surface as the adsorption site, where one gas molecule is allowed to interact. Conversely, for the adsorption of the two molecules, a larger site like a coronene ring is used for the high layer. Adsorption energy, Gibbs free energy change, Mulliken charge transfer, and total electron-density maps are computed in each case. The adsorption strength of the gas molecule on the SnCNT surface is also analyzed from the density of states projected to different atoms (PDOS) of the nanotube-adsorbate complexes. The adsorptions of CO and N2 on the (6,0) SnCNT surface require to cross potential barriers, and the corresponding transition structures are identified by ONIOM-IRC calculations. For the remaining four molecules, the processes of adsorption are predicted to be barrier-less. The calculations for the adsorption of H2CO on (5,0) and (7,0) SnCNT surfaces are extended to study the effect of the size of the nanotube. Results for the adsorption of a single molecule on (6,0) SnCNT using B3LYP functional are compared with those obtained from a dispersion corrected functional such as M06-2X. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]