Dear all! I would like to calculate the sound velocity for graphene. It seems rather simple but I have encountered a problem which I still can't solve. I have calculated the phonon band structure which seems reasonable and have got the frequencies near gamma point (in cm-1). Now I should just derivate omega (in s-1 = cm-1*3*10^10) by k and obtain velocity. But the what units of k should I use? The k units using in PWSCF is 2*pi/a0 where a0=4.66625 Bohr = 2.13 Ang and it seems correct.
The reciprocal lattice vectors are following: b(1) = ( 1.0000 0.5774 0.0000 ) b(2) = ( 0.0000 1.1547 0.0000 ) b(3) = ( 0.0000 0.0000 0.1900 ) But when I try to evaluate the velocity I obtain the answer nearly in six time less then reported early: 2200 m/s and 3400 m/s vs. 12200 m/s and 19500 m/s. I do some stupid mistake, but where? Does anybody has the experience in such calculations? Thank you!! -- Sincerely yours, Pavel B Sorokin mailto:PBSorokin at gmail.com -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100324/ff3947fc/attachment.htm
