Stochastic search for isomers on a quantum mechanical surface

In Studying molecules with Unusual bonding and structures, it is desirable to be able to find all the isomers that are minima on the energy surface. A stochastic search procedure is described for seeking all the isomers on a surface defined by quantum mechanical calculations involving random kicks followed by optimization. It has been applied to searching for singlet structures for C-6 using the restricted Hartree-Fock/6-31 1G basis set. In addition to the linear chain and ring previously investigated, 11 additional structures (A-K) were located at this level. These provide a basis for discussing qualitative bonding motifs for this carbon cluster. The application of a similar idea to searching for transition states is discussed. (C) 2004 Wiley Periodicals, Inc.