[Pw_forum] negative frequency in high q-mesh

[Lorenzo Paulatto]

On 31 January 2013 08:32, Wei-Bing Zhang <weibingzhangavh at gmail.com> wrote:

> (i.e vc-relax directly and
> atomic relaxation with different lattice parameters).
>

Dear Wei,
please triple-check that you are doing everything correctly:
* that after the relax you are putting back the final parameters in the pw
input
* that in the SCF calculation that precedes the phonon one, forces and
stress are actually zero

I would also suggest to NOT play to input parameters: you are using
input_dft and exx_div_threatement both of which do not apply in your case.
Finally, ecutwfc = 65 is incredibly high for a Si ultrasoft
pseudopotential. Try to read something about this subject i.e. here <
http://www.stanford.edu/~hkulik/www/Tutorials/Entries/2012/4/17_Convergence_101.html>
(the "dual" is ecutrho/ecutwfc)

bests


-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20130131/793096f9/attachment.html>