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O: Fachverband Oberflächenphysik

O 67: Ab-initio approaches to excitations in condensed matter III

O 67.6: Vortrag

Freitag, 27. März 2009, 12:30–12:45, SCH 251

Electron-phonon coupling in graphite within the GW-approximation — •Ludger Wirtz¹, Michele Lazzeri², Claudio Attaccalite³, and Francesco Mauri² — ¹IEMN, Lille France — ²IMPMC, University "Pierre et Marie Curie", Paris, France — ³European Theoretical Spectroscopy Facility, University of the Basque Country, San Sebastian, Spain

A seemingly trivial thing such as the phonon dispersion of graphite continues to present surprises. For most materials (both metals and insulators), density-functional perturbation theory using LDA or GGA gives phonon dispersions in close agreement with experimental results. For graphene and graphite, however, there is a pronounced failure of LDA and GGA for the highest optical phonon branch (HOB) around the Kohn-anomaly at the high-symmetry point K. We evaluate the electron-phonon coupling (EPC) between the pi-bands and the HOB in the GW-approximation. Non-local exchange-correlation effects renormalize the square EPC by almost 80%. This almost doubles the slope of the HOB around K and explains recent experimental results on graphite-phonons using inelastic x-ray scattering and double-resonance Raman spectroscopy. The short-coming of LDA and GGA may be partially fixed by the use of hybrid-functionals such as B3LYP (which partially contains exact Hartree-Fock exchange). The use of pure Hartree-Fock, however, leads to an extremely strong EPC and consequently to an instability of graphene under distortion along the HOB phonon.