Inhomogeneous electron liquid in the free-space building block Li2C2 plus its dimer and trimer

Quantum-chemical calculations are first reported on the building block Li2C2. Two low-lying isomers are predicted, and hence the equilibrium ground-state geometry by the coupled cluster method (CCSD). The ground-state is non-linear, contrasting with the other planar isomer. The dimer (Li2C2)(2) is then examined by the Hartree-Fock plus second-order Moller-Plesset (HF+MP2) method. The ground-state geometry is predicted to have C-4 on a linear chain. As to the trimer, the C-6 atoms are predicted at the same ab initio level to lie on a hexagon. But the Li atoms prefer each to bond to two C atoms, rather than reproduce the geometry of benzene. Finally, some contact is made with a recent density functional theory study of solid lithium carbide under pressure.