[QE-users] Phonon Dispersion of SrTiO3, EuTiO3 using Hubbard

[Paolo Giannozzi]

On 12/06/2022 12:00, simon rombauer wrote:

>      1) Why is it not possible to set epsil = .true., lraman .true. ? 

because the system is (treated as) a metal: you are using a broadening

>      2) Is it normal that the ph.x code takes a lot of comupting time 
> compared to pw.x scf, nscf, bands calculations? (ETO phonon at gamma 
> took over 13 h)

it depends. Plain (GGA, normconserving) phonon calculations should take 
no more time than (a small factor depending upon the phonon wave-vector) 
* (time needed for a scf calculation) * (number of linear-response 
calculations = 3* number of atoms * number of wave-vectors). Ultrasoft 
phonons are definitely slower. DFT+U don't know, might be slower as 
well. It depends upon the number ot terms appearing in the 
linear-response calculation

>      3) Almost all phonon frequencies are negative, which indicates 
> instabilities in the system (?), I've run vc-relax calculations and used 
> the new lattice parameters but got the same results, any idea what these 
> negative frequencies could tell me?

(negative => imaginary actually) You should first of all figure out 
whether they are an artifact of the calculation or not. For sure, your 
threshold for linear-response convergence (tr2_ph) is too large. Have 
you tried a simpler version of a similar system?

>      4) Is it possible obtain the dielectric function for these 
> materials in a different way?

For effective charges you may use the Berry's phase approach

> I hope you are still around and thank you for reading :)

if you are referring to the mailing list: yes, it still works, except 
for people using @gmail.com addresses, and for those who don't check 
their spam folder :-(

Paolo
> 
> Have a nice day,
> 
> Simon Rombauer
> Physics student
> University of Augsburg
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222