The importance of global minimization and adequate theoretical tools for cluster optimization: the Ni6 cluster case

A Monte Carlo simulated annealing (MCSA) algorithm using parallel processing has been employed in quantum parametric method in order to full optimize the Ni6 cluster. Results obtained from this procedure show that the same trend is reproduced by standard DFT optimization calculations. However, results do not correspond with the octahedral geometry reported in several theoretical DFT calculations and for classical global minimization techniques. Different structures close in energy are found here, as the most stable ones: pentagonal pyramid (PPY) and capped trigonal bipyramid (CTB).