By Michael Collins
Research School of Chemistry, Australian National University

Systematic molecular fragmentation describes a molecule in terms of a set of small molecular fragments. A systematic rule provides a hierarchy of estimates for the energy, structure, vibrational frequencies and other properties, of large molecules in terms of the corresponding quantities for the small fragments. The approach requires a computation time that scales linearly with the size of the molecule, or is independent of molecular size if sufficient processors are available. The method can be efficiently applied to molecules (large or small), to molecular clusters, and to non-conducting crystals. Here, the method is illustrated using a number of examples: the energies and vibrational frequencies of molecules containing explicit charges; the NMR shielding constants for proteins of thousands of atoms; and energies of small absorbate molecules in porous materials.