CLUSTER STRUCTURE DETERMINATION USING GAUSSIAN DENSITY DISTRIBUTION GLOBAL MINIMIZATION METHODS

Classical particle density distributions, approximated by floating Gau ssians, are used to efficiently sample different structures in order t o locate the global minimum on the multidimensional potential surface of van der Waals and water clusters. The Gaussian density annealing (G DA) approach of Ma and Straub [J. Chem. Phys 101, 533 (1994)] provides a set of equations of motion for Gaussian widths and centers. These e quations are used to anneal the system from high temperature, with lar ge Gaussian widths describing the particle density distribution, to lo w temperature. In order to ensure a quasiequilibrium throughout this p rocess, certain constraints are imposed during the annealing. The resu lts of structure optimization of van der Waals clusters using differen t variants of the GDA are compared. These applications demonstrate the advantage and efficiency of our method, a variation of the GDA algori thm, which anneals on consecutive levels of lower temperature. Extensi ons of the approach for atomic systems to include rigorous bond constr aints in molecular clusters are also presented. Water cluster structur es are investigated and compared with other theoretical calculations. Our findings suggest that the nature of the underlying free energy sur face may diminish the efficacy of the GDA, and related methods, in loc ating global minima for clusters.