Reexamination of the structures and energies of Li2C2 and Li4C4

The structures and energies of Li2C2 and Li4C4 have been reexamined by DFT and MP2 methods using a variety of basis sets of 6-311+G(3df) and cc-pVXZ(X = T,Q,5). Two low-lying isomers are found as the local minima on the potential energy surfaces of Li4C4. The lowest energy structure is shown to be multiply bridged D2h form. A newly found quadruply bridged Ci form is found to be a local minimum, lying in energy above D2h form by 22 kJ/mol in the energy. Also the energetics of high-lying isomers such as tetralithiotetrahedrane isomers were evaluated and discussed.