Polarization and Covalency in Alkali-Tetralide Clusters
  In this paper we discuss the structure of A4M4 alkali(=A)- tetralide (= M) (= group 14) clusters. Without polarization these polyions consist of a central tetralide tetrahedron with each face capped by an alkali ion. We show that ionic polarization can lead to quite different cluster structures by breaking up of the tetralide tetrahedron into pairs M_2, and it can even destroy covalent bonds in these clusters. Consequences for the structure of the solid, liquid and amorphous phase are discussed. 
Wiebe Geertsma