[QE-users] I have failed to reproduce phonon DOS of germanium

[mkondrin]

Hi, Paolo!

Thank you for the hints. I will try all of them.

Sincerely yours,
Mikhail Kondrin

On 23.12.2020 20:09, Paolo Giannozzi wrote:
> On Wed, Dec 23, 2020 at 1:46 PM mkondrin <mkondrin at hppi.troitsk.ru> wrote:
>
> &SYSTEM
>>     ibrav = 0
>>     A =   5.658
>>
> A is the experimental lattice parameter and would be fine for ibrav=2
> (fcc), but then you set your lattice vectors:
>
> CELL_PARAMETERS (alat= 10.69207046)
>>    -0.510237966   0.000000000   0.510237966
>>     -0.000000000   0.510237966   0.510237966
>>     -0.510237966   0.510237966   0.000000000
>>
> to a larger cell (they are in "alat" unit, that is, the value specified as
> "A" or "celldm(1)", NOT the value in the card). With ibrav=2 you get
> something like 290 cm^-1. Note that the phonons are typically computed at
> the theoretical equilibrium lattice parameter, that in LDA is typically
> smaller than the experimental, leading to higher frequencies.
>
> Also note that the convergence threshold conv_thr=1.e-5 in the scf
> calculation is too large: reduce it to at least 1.0e-8 (it costs close to
> nothing with respect to the phonon calculation)
>
> Paolo
>
>
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