[QE-users] problem using vc-relax with organic crystal structure

[Paolo Giannozzi]

For the kind of pseudopotentials used in the calculation (not the best ones
by the way), the cutoffs are definitely too small.  It is evident from the
large difference between the energy of the final configuration, computed
for the basis set of the starting cell (-1301.20336608 Ry) and for the
basis set of the final cell (-1296.98258973 Ry).

This looks like a molecular crystal. The determination of equilibrium cell
is rather delicate.

Paol

On Wed, Dec 2, 2020 at 7:39 PM Claudio A. Perottoni <caperott at gmail.com>
wrote:

> Dear Corrado,
>
> The ecutwfc in your input file seems a bit small. You may try using
> https://www.materialscloud.org/work/tools/qeinputgenerator to generate an
> input file for optimizing the crystal structure of your compound.
> Best regards,
> Claudio
>
>
> On Wed, Dec 2, 2020 at 3:15 PM Cuocci Corrado <corrado.cuocci at gmail.com>
> wrote:
>
>> I have determined the crystal structure of new organic compound from
>> X-ray powder diffraction data.
>>
>> First of all, I used quantum espresso to validate my new structure in a
>> 'relax' calculation obtaining a result in a good agreement with the
>> experimental structure.
>>
>> In a second step I tried to perform a 'vc-relax' but in this case the
>> result seems chemically unreasonable: I observed a large variation of
>> the cell parameters, final density too high for this type of compound,
>> short intermolecular distances.
>> Input and output files can be downloaded from:
>> https://cloud.ba.cnr.it/index.php/s/5RmA7MqA9gJeRdx/download
>> https://cloud.ba.cnr.it/index.php/s/qmnAwM5JeqDnHdG/download
>>
>> My experience in the use of the program is limited and I suspect I have
>> made some mistakes.
>> Do you have any suggestions to improve the calculation?
>>
>> Thanks a lot.
>> Corrado
>> --
>> ============================================
>> Cuocci Corrado
>> Istituto di Cristallografia - CNR
>> Via G. Amendola,122/o
>> 70126 Bari (Italy)
>> tel: +390805929161
>> fax:+390805929170
>> corrado.cuocci at ic.cnr.it
>> ============================================
>> _______________________________________________
>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
>> users mailing list users at lists.quantum-espresso.org
>> https://lists.quantum-espresso.org/mailman/listinfo/users
>>
>
>
> --
>
> *Claudio A. Perottoni*
>
> Universidade de Caxias do Sul
> 95070-560 Caxias do Sul - RS - Brazil
> http://www.researcherid.com/rid/B-8409-2008
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users



-- 
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
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