Energy Controlled Edge Formation for Graphene Nano Ribbons

On the basis of first principles calculations, we report energy estimated to cut a graphene sheet into nanoribbons of armchair and zigzag configurations. Our calculations show that the energy required to cut a graphene sheet into zigzag configuration is higher than that of armchair configuration by an order of 0.174 eV. Thus, a control over the threshold energy might be helpful in designing an experiment for cutting a graphene sheet into smooth edged armchair or zigzag configurations

Rotational transitions of COH+ and He: New interaction potential, bound states, scattering and pressure broadening cross-sections

We present new calculations of a metastable isomer of HCO+, i.e. COH+ in collision with He. The COH+ has been suggested as an alternative molecular hydrogen tracer, which makes it of great interest for astrophysical studies. COH+ was first observed in astronomical space towards SgrB2 with the observation of J=1→0, J=2→1 and J=3→2 lines. Calculations are based on new ab initio potential energy surfaces (PES) of charged complex COH+-He using the CCSD(T) in conjunction with aug-cc-pVQZ basis set. The PES has a well depth of -836.5 cm−1 towards H-end at the COH+−He distance (R) of 2.9 ˚A in linear orientation. To test the new PES, the calculations of the bound-state are carried out and pressure broadening cross-sections of COH+ with He collisions are computed for kinetic energies up to 150 cm−1 using the accurate close-coupling method. Further, the pressure broadening and shift coefficients have been calculated from the corresponding real and imaginary parts of cross-sections for the first six rotational transitions. The data obtained is found to be in the same order as the HCO+-He system. Further, we have computed the rate coefficients and compared the results with the reported COH+-He and HCO+-He data. The results generated by this study is believed to be useful for both laboratory and future astrophysical research

Fundamental Study of Reversible Hydrogen Storage in Titanium- and Lithium-Functionalized Calix[4]arene

Hydrogen is the most promising candidate for a sustainable energy source in the transport sector. However, the storage of hydrogen is a major problem. Calix[4]­arene (CX) is functionalized with Ti and Li metals on the delocalized π electrons of benzene rings, and the metal-functionalized system is studied for hydrogen storage efficiency by applying density functional theory using the M06 hybrid functional and 6-311G­(d,p) basis set. The calculated binding energy indicates Ti coordinates with CX strongly while Li coordinates weakly and the binding of CX and metal is through Dewar mechanism. On saturation with hydrogen, each Ti atom traps four H₂ molecules while each Li atom traps three H₂ molecules on CX. Hydrogen molecules are adsorbed on the metal atoms by Kubas–Niu–Rao–Jena interaction. The global reactivity index obtained for the system obeys the maximum hardness and minimum electrophilicity principle. Molecular dynamics simulations are performed using spin-polarized generalized gradient approximation with the Perdew–Burke–Ernzerhof functional including Grimme diffusion parameter on H₂ saturated systems. The dissociation of H₂ molecules in the Ti-functionalized CX system begins from 273 K, while all the H₂ molecules are desorbed by 473 K. The storage capacity is found to be 8.7 wt % for Ti and 10.1 wt % for Li-functionalized CX. When the Ti atom is intercalated between the two CX moieties, the storage capacity does not reduce significantly. This study reveals that the Ti-functionalized CX is a potential reversible hydrogen storage material