Stability of superdense lithium graphite compounds

We have calculated total energies for LiC2 and LiC3, superdense lithium graphite compounds, and have compared the equilibrium parameters with the measured data. Both theory and experiment agree that LiC2 is metastable at ambient pressure. Furthermore, the calculations predict the existence of a stable phase for LiC3 with lattice constants a and c in excellent agreement with the measured values within 2.6% and 1.2%, respectively. However, the calculations cannot reproduce the +/- 0.4 angstrom vertical offset of Li atoms from the plane halfway between the carbon layers. (C) 2007 Elsevier Ltd. All rights reserved.