[Pw_forum] SCF calculation input

[Kyeong-hyun Park]

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,
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