The interplay between structure and orbitals in the chemical bonding of graphite

Recently, the dynamics of atomic distances and orbital charge in graphite has been investigated by ultra-fast electron diffraction, electron energy loss spectroscopy and transient optical absorption. A subtle interplay between structural motions and electronic degrees of freedom was found responsible for several peculiar behaviors like coherent phonon emission, photoinduced diamond formation, and graphene ablation. Here, we calculate ab initio the charge density of graphite, and observe its evolution during the above-mentioned structural distortions. The modifications of the electron energy loss and the optical spectra during c-axis compression and expansion are calculated and found in agreement with recent experiments. (C) 2010 Elsevier B.V. All rights reserved.