Interaction effects on electric susceptibilities: A model study of polarizabilities of the Be atom embedded in He clusters

The beryllium atom embedded in He clusters of octahedral and cubic symmetry is studied as a model of a highly polarizable system surrounded by a relatively inert and weakly polarizable medium. The coupled cluster calculations with single and double excitations corrected for triple excitations predict that the dipole polarizability and hyperpolarizability of the `in-clusterʹ Be atom are significantly reduced in comparison with the free-atom values. In the vicinity of the van der Waals minima this reduction amounts to about ten percent of the Be atom hyperpolarizability. This orbital compression effect shows that in the modeling of highly nonlinear optical materials one must explicitly consider the presence of the medium.