Bonding in the Mg4 cluster. An example of chemical bonding originating from electron correlation effects

Abstract
The Mo4 cluster has been examined with SCF and correlated SCEP and CEPA‐2 treatments. It is found that little or no binding is obtained when either correlation effects of atomic 3d functions in the basis set are excluded. However, calculations including correlation effects and utilizing a basis set containing d functions demonstrated chemical bonding and yield A cluster formation energy of about 20 kcal/mole.