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

[Stefano Baroni]

Besides, intermolecular distances in a molecular crystal sensitively depend on the XC functional, all of which have a hard time properly accounting for dispersion forces (some of them a worse time than others). SB

> On 2 Dec 2020, at 19:38, 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 <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 <mailto: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/5RmA7MqA9gJeRdx/download>
> https://cloud.ba.cnr.it/index.php/s/qmnAwM5JeqDnHdG/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 <mailto:corrado.cuocci at ic.cnr.it>
> ============================================
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> 
> 
> -- 
> Claudio A. Perottoni
> Universidade de Caxias do Sul
> 95070-560 Caxias do Sul - RS - Brazil
> 
> http://www.researcherid.com/rid/B-8409-2008 <http://www.researcherid.com/rid/B-8409-2008>_______________________________________________
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