DELOCALIZATION OF A HOLE IN VAN-DER-WAALS CLUSTERS - IONIZATION-POTENTIAL OF RARE-GAS AND SMALL HGN CLUSTERS

The size dependence of the ionization potential I(p)(n) of van der Waals (vdW) bound clusters has been calculated by using a model Hamiltonian, which includes electron hopping, vdW interactions, and charge-dipole interactions. The charge-density and dipole-density distributions for both neutral and ionized n-atom clusters are determined self-consistently. The competition between the polarization energy of the neutral atoms surrounding a partially localized hole and the tendency toward hole delocalization in the ionized clusters is found to dominate the size dependence of I(p)(n). To test our theory, we calculate I(p)(Xe(n)) and I(p)(Kr(n)) for n < 300. Good quantitative agreement with experiment is obtained. The theory is also applied to calculate I(p)(Hg(n)). Comparison with experiments suggests that in Hg(n +) clusters with n < 20 the positive charge is mainly distributed within a trimer which is situated at the center of the cluster and which polarizes the n - 3 surrounding neutral atoms.