The catalytic profile and function of each component of a molybdenum-graphene based catalyst (Mo/N-doped graphene) for nitrogen fixation, which combines the merits of these two components, is evaluated computationally. The Mo/N part acts as an active centre for N2 bond breaking and the graphene part works as an electron transmitter and electron reservoir.
Computer simulation studies of nanoscale materials, in particular nanoparticles or finite-length nanotubes/nanowires, via ab initio methods are challenging or impossible due to computational costs associated with the calculation of total energy and atomic forces of nanometer-sized systems. While molecular mechanics methods can handle large systems, they cannot describe manifestations of quantum effects in nanoscale materials. Therefore, we have developed a quantum-mechanics based semi-empirical Hamiltonian to bridge the accuracy and system-size gap between the above two methods. The key feature of this self-consistent and environment dependent (SCED) Hamiltonian is that it takes into account of environment-dependency, electron screening, and charge re-distribution effects within the LCAO (linear combination of atomic orbitals) framework. In the present study, we have used a relaxation scheme based on the SCED/LCAO Hamiltonian to determine the structure and electronic density of states of multi-shelled fullerenes ("fullerene onions") up to six shells. Our study reveals that inter-shell interactions are weak with a small charge transfer from the outer to the inner shells. The structure (or geometry) of fullerene shells in the onion structure is very similar to the geometries of corresponding isolated fullerenes, and, therefore, the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of a fullerene onion is similar to that of the corresponding outermost shell.
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