SYSTEMATIC STUDY OF THE LOWEST ENERGY-STATES OF PD, PD-2, AND PD-3

A systematic study has been carried out for the determination and char acterization of the lowest states of Pd, Pd-2, and Pd-3 using some of the best ab initio tools available at present (conventional and DFT). Full electron ab initio calculations using the HF, MP2, MP3, MP4, and QCI methods were compared with DFT methods using several gradient-corr ected functionals as well as the hybrid B3LYP functional that performe d very well for the energetics studies of these small clusters. A suit able basis set has been found to perform considerably well with pallad ium atoms, another of double-zeta quality has been found insufficient to reproduce basic characteristics of the smallest palladium clusters. The results indicate that the ground state for Pd is a singlet. The d imer is a triplet; however, it is very difficult to ascertain due to t he closeness between singlet and triplet states (0.9 kcal/mol). The tr imer ground state was found to be a triplet with a separation from the lowest singlet of 3.2 kcal/mol. The lowest triplet and singlet of Pd- 3 were practically equilateral triangles. (C) 1997 John Wiley & Sons, Inc.