GLOBAL GEOMETRY OPTIMIZATION OF (AR)(N) AND B(AR)(N) CLUSTERS USING AMODIFIED GENETIC ALGORITHM

A modified deterministic/stochastic genetic algorithm (DS-GA) method i s proposed for the determination of the global minimum of atomic clust ers described by pairwise analytic interaction potentials. Our modific ation of the standard GA method involves a coarse local minimization o f each member of the population at every generation, as well as includ ing the gradient into the fitness function. For Lennard-Jones (Ar)(n) clusters with n<30, the DS-GA converges far more quickly to the global minimum than either conventional GA methods or random search procedur es. An application of this DS-GA is made to heterogeneous clusters of B(P-2) with multiple Ar atoms. The interaction potential is given by t he lowest state of a 3X3 electronic Hamiltonian. The Ar-Ar potential a nd the lower energy (IT state) B-Ar potential are very similar. In con trast, the higher energy (Sigma state) B-Ar interaction is essentially repulsive. Consequently, the B atom is nearly always found to substit ute for one of the atoms in the corresponding (Ar)(n+1) cluster with t he fewest number of nearest neighbors. (C) 1996 American Institute of Physics.