The effects of core (3d) correlation on chemisorption

Large-scale calculations using atomic natural orbital (ANO) basis sets have been performed on Cu5O to establish the effects of correlation of the 3d shell on oxygen chemisorption. The largest calculation performed correlated 51 electrons in a basis set containing 205 ANO’s. Correlation of the 3d shell is found to increase the chemisorption energy by 13(16±2) kcal/mol and decrease the height above the surface of the oxygen by 0.23(0.38) a0 with CI superposition error corrections included. The 2E state of the bare cluster is found to be stabilized by 10(8) kcal/mol relative to the 4A2 state as a result of 3d correlation. The values in parentheses were obtained using an approximate core–valence correlation operator which thus gives results in very good agreement with the core correlated calculations.