[Pw_forum] Convergence test w.r.t 'tr2_ph'

[Kyeong-hyun Park]

Hello all,

For the phonon dispersion calculation, I've done the convergence test by
'vc_relax' calculation and re-assigned the lattice parameters (celldm(1),
celldm(4), conv_thr, and ATOMIC_POSITIONS). However, my phonon dispersion
still behave a bit weird (negative acoustic frequency, LO-TO splitting).

My structure is very complicated, rhombohedron with 5 basis, and now I
guess it might be the convergence threshold (tr2_ph). My 'tr2_ph' has been
set as '1.0d-14'

I am looking for the way of finding a proper tr2_ph value. Is there any
convergence test for that? My simulation would run more than 50 hrs, so I
don't want to just give it a shot with randomly picked value.

Thanks as always.

Best,
Kyeong
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