Structural and electronic properties of lithium intercalated graphite LiC6

We calculate the lattice properties and electronic structure of graphite and LiC6 within the most widely used density-functional theory implementation, the local density approximation (LDA). Improvements to the LDA in the form of a generalized gradient approximation (GGA) are explored. Structural parameters predicted by the LDA, as expected, underestimate experiment within a 1%-2% margin of accuracy. The GGA does not give a good account in the prediction of lattice parameter c, especially in graphite, although it does give a reliable description of LiC6. The effect on intercalating lithium into graphite, where charge transfer from lithium to carbon layers (graphenes) is expected, is discussed from the valence charge density, partial density of states, and energy band structure plots. The latter plot is also compared with inelastic neutron scattering results and low-energy electron diffraction results. We extend this work by calculating the elastic constants and bulk modulus for both graphite and LiC6 structures. These results are in excellent agreement with the available experimental data. The calculated hydrostatic pressure dependence of the crystal structures is also found to be in good agreement with the results of high-resolution x-ray structural studies and with other experimental data as well as with other calculations. The analysis of electronic structure at 0 GPa (ambient pressure) is used to resolve inconsistencies between previous LDA calculations.