Molecular structures and energies of low-lying clusters: Comparison with clusters

The structures and energies of Li x Si x ( x = 1 – 4 ) were investigated by the DFT and MP2 methods by using a variety of basis sets of 6-31G(d), 6-311+G(2df), and cc-pVXZ (X = T, Q, 5). Two singlet low-lying doubly-bridged bent ( C 2 v ) and planar ( D 2 h ) structures are found to be the global minimum and a transition state on the potential energy surface of Li 2 Si 2 , respectively. The preference of polylithium compounds Li x Si x ( x = 2 – 4 ) for nonclassical structures can be taken as an indication that the extensive bonding prevails presumably owing to ionic contribution.