Kr. Kganyago et Pe. Ngoepe, Effects of local and gradient-corrected density approximations on the prediction of the intralayer lattice distance c, in graphite and LiC6, MOL SIMULAT, 22(1), 1999, pp. 39
Ab initio total energy calculations, on hexagonal models of graphite and Li
C6, are carried out within the most widely density functional theory (DFT)
implementation, the local density approximation (LDA). Improvements to LDA
in the form of generalized gradient approximation (GGA) are explored. Struc
tural parameters predicted by LDA, as expected underestimate experiment wit
hin 1-2% margin of accuracy. GGA does not give a good account in the predic
tion of lattice parameter c, especially in graphite. This is evident in bot
h recently implemented gradient corrections by Perdew and Wang and earlier
corrections by Becke approximations. A substantial improvement is seen on i
ntroducing lithium ion in LiC6 and using recent approximations. Valence ele
ctron densities from both LDA and GGA calculations, shows charge distributi
on plots that compare well with experimental results. Charge density distri
bution plots of these approximations appears similar on a larger scale.