First-principles calculation of the lattice parameters of graphite at high temperature and high pressure

The lattice parameters of graphite at high temperature and high pressure were computed using ab initio density-functional theory with the generalized gradient approximation and the local density approximation respectively. Good agreement was achieved between the calculated and experimental results in lattice parameters a, with the maximum relative differences being 1.2%. Meanwhile, the calculated lattice parameters c were also reasonably consistent with the experimental results with the maximum relative difference being 8.9%. It was also found that both a and c/a increased slowly with temperature, but decreased dramatically with pressure, indicating the greater impact of pressure on the lattice parameters.