Optimization of bimetallic Cu-Au and Ag-Au clusters by using a modified adaptive immune optimization algorithm

A modified adaptive immune optimization algorithm (AIOA) is designed for optimization of Cu-Au and Ag-Au bimetallic clusters with Gupta potential. Compared with homoatom clusters, there are homotopic isomers in bimetallic cluster, so atom exchange operation is presented in the modified AIOA. The efficiency of the algorithm is tested by optimization of Cu(n)Au(38-n) (0 < or = n < or = 38). Results show that all the structures with the putative global minimal energies are successfully located. In the optimization of Ag(n)Au(55-n) (0 < or = n < or = 55) bimetallic clusters, all the structures with the reported minimal energies are obtained, and 36 structures with even lower potential energies are found. On the other hand, with the optimized structures of Cu(n)Au(55-n), it is shown that all 55-atom Cu-Au bimetallic clusters are Mackay icosahedra except for Au55, which is a face-centered cubic (fcc)-like structure; Cu55, Cu12Au43, and Cu1Au54 have two-shell Mackay icosahedral geometries with Ih point group symmetry.