Comparative QM/MM studies of H2 adsorption on lithium doped single walled armchair and zigzag nanotubes: SiCNT, GeCNT, and SnCNT

Abstract

AbstractBinding 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.