Dear QE developers and users, I've calculated phonon dispersion for alpha-quartz. It gives for acoustic branches at Gamma --- A direction:
q (2*pi/a_0) ? ? ? omega_1 ? omega_2 ? omega_3 (cm^(-1)) ------------------------------------------------------------------ 0.00000000 ? ? ? -1.1614 ? ? ?-0.8602 ? ? ? -0.7608 0.045470455 ? ? ?9.2277 ? ? ?18.1443 ? ? 24.0697 0.09094091 ? ? ? 21.8192 ? ? 34.5505 ? ? 47.4024 . . .Differentiating these dispersion relations I found that the speed of the "fastest" sound waves is about 1000 m/sec, while the simple mechanical calculation (as well as reference data) gives at least a five times larger value. My scf input: &control calculation='scf', restart_mode='from_scratch', prefix='sio2', pseudo_dir = '/home/user/espresso/pseudo', outdir='/home/user/espresso/tmp' / &system ibrav=4, celldm(1)=9.289897331, celldm(3)=1.099552482, nat= 9, ntyp= 2, ecutwfc = 20.0 ecutrho = 150.0 / &electrons electron_maxstep=1000 mixing_mode = 'plain' mixing_beta = 0.7 conv_thr = 1.0d-8 / ATOMIC_SPECIES Si 28.086 Si.pw91-n-van.UPF O 15.999 O.pw91-van_ak.UPF ATOMIC_POSITIONS crystal Si 0.465976452 0.000000000 0.000000000 Si -0.000045477 0.465778133 0.666710600 Si -0.465823610 -0.465778133 0.333289400 O 0.410406470 0.274336629 0.112688982 O -0.274215479 0.135800008 0.779283047 O -0.136110820 -0.409868933 0.446516439 O 0.273758113 0.409868933 0.553483561 O -0.410015489 -0.135800008 0.220716953 O 0.136069841 -0.274336629 -0.112688982 K_POINTS automatic 4 4 4 0 0 0 Phonon input: phonons of SiO_2 &inputph tr2_ph=1.0d-12, prefix='sio2', ldisp=.true., nq1=2, nq2=2, nq3=2 amass(1)=28.086, amass(2)=15.999, outdir='/home/user/espresso/tmp', fildyn='sio2.dyn', / Does anyone know the origin of such?discrepancy??Regards, Mikhail Goncharovskii, postgraduate student, Omsk State University, Russia ------------------------------------------------------------------------------------------------------------------- Please, if possible, don't send me MS Word or PowerPoint attachments. Why? See: http://www.gnu.org/philosophy/no-word-attachments.html -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20120109/97c50ce4/attachment.htm
