CORE VALENCE CORRELATION-EFFECTS ON SOME CU CLUSTERS

The effects of core-valence correlation on the properties of several Cu clusters (Cu5, Cu5H and Cu5O) are investigated using a model operator technique and for Cu5H also explicit CI techniques using a large atomic natural orbital (ANO) basis set. Core-valence correlation increases the Cu5 cluster binding energy by 25 kcal/mol and the ionization potential by 0.42 eV. The atomic chemisorption energy of oxygen on Cu5 is increased by 15 kcal/mol and the height of oxygen and hydrogen above the surface is decreased by 0.35 and 0.21 a-0 respectively when core-valence correlation is included. The sensitivity of the results to the parametrization in the model operator is investigated and found to be small. Good agreement is found between the results obtained using the model operator and with the 3d electrons explicitly correlated.