Dear all, I am curious if some of you have experience with the following: in normal LDA/GGA calculations my graphene phonon dispersions always end up with a small problem at the "M" point of the BZ; the highest optical mode is split from the lower mode by maybe 50/cm (almost all published papers show this, for example PRB 78 081406(R) (2008). In all my calculations the highest mode "collapses" and the splitting vanishes when I increase the k-grid and/or q-grid, in this sense the phonon dispersion converges to a final form but not the "right" one.
Now I know that graphene is tricky to converge but with inputs as in the above cited paper (k=18x18x1) and a q-grid (9x9x1) the phonon dispersion looks OK, at k=72x72x1 and q=12x12x1 it looks fairly bad. Anyone got a similar experience and maybe a solution? Thanks in advance! Best, Chris -- Postdoctoral Researcher Center for Quantum Nanoscience, Institute for Basic Science Ewha Womans University, Seoul, South Korea
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