With this grant in the Theoretical and Computational Chemistry Program of the Chemistry Division, Professor Gimarc will develop qualitative theoretical models to explain the basic nature of molecular structure and bonding in clusters of elements in the main group of the periodic table. Clusters of homoatomic main group elements will be studied in order to form a qualitative molecular orbital model with which to relate the various structures within a given cluster class. Molecular orbitals and molecular structures will be generated by geometry optimized ab initio SCF MO calculations at various levels of basis set accuracy. Correlation diagrams for energy levels in various possible shapes will be constructed and interpreted using atomic orbital composition diagrams. This will allow the PI to develop an understanding of the relative stabilities of the various possible cluster structures.