Hi all, I am doing the phonon dispersion calculation of bismuth telluride whose structure is rhombohedron with 5 basis. Until now, I have kept getting incorrect frequencies: negative or different optical frequencies near gamma point according to the propagation direction.
After I got an advise from Dr. Lorenzo about a possible convergence problem, I've set the lattice parameters based on the convergence test (celldm(1), celldm(4), conv_thr, ATOMIC_POSITIONS) and used 'tr2_ph=1.0d-14' in ph.x calculation. (with tr2_ph=1.0d-16, it didn't converge after 100 iterations) Here below are the scf inputs that I used. I wonder if I missed anything which is critical or used a wrong value for the calculation. Please give any suggestion you can think of. --------------------------------------------------------------- &system ibrav=5, celldm(1)=17.521, celldm(4)=0.8451, nat=5, ntyp=2, ecutwfc=100.0 / &electrons conv_thr = 1.0d-12 mixing_beta = 0.7 / ATOMIC_SPECIES Bi .... mass pseudopotential Te ... ATOMIC_POSITIONS alat .... .... .... .... .... K_POINTS automatic 4 4 4 1 1 1 ---------------------------------------------------------------- Thank you. Best, -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121107/01c15f7a/attachment.html
