Spatial structure of Au8:: Importance of basis set completeness and geometry relaxation

The relative stabilities of the lowest energy structures are calculated for the gold octamer, Au-8, employing highly correlated ab initio methods. The question of dimensionality of these clusters is addressed, and a guideline for future structural studies of such systems is provided. In particular, the importance of geometry relaxation beyond the MP2 level of theory as well as the need for basis sets toward the complete limit (CBS) are discussed. The planar D-4h symmetric structure of Au-8 is the lowest energy structure. At the CCSD(T)/CBS limit, it is separated by 16 kJ mol(-1) from the next higher T-d symmetric isomer.