[QE-users] Which pressure should I report on my work???

[Bidault, Xavier]

Hello,

As said by Giuseppe, the pressure criteria could be tightened. However I also noticed that this difference between the last step of the vc-relax stage and the "verification" step where the basis set is recalculated happens when the energy cutoff is not large enough. For instance, for the CHON materials I studied using PBE-D2 and PSlib 1.0.0, this happens if the energy cutoff is lower than 60 Ry. So the solution may also be to increase this parameter.

Best regards,
Xavier


________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it>
Sent: Sunday, September 20, 2020 5:20 AM
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] Which pressure should I report on my work???


Dear Mohaddeseh
If you want to apply a pressure closer to the target, then you can
lower the value of press_conv_thr to 0.1 or even 0.01.
HTH
Giuseppe

Quoting Stefano Baroni <baroni at sissa.it>:

> What is difference between the frequencies computed at: i) P=0; ii)
> P=6.57 kbar;  iii) 7 kbar? The answer to my question will imply that
> to yours. SB
>
> —
> Stefano Baroni -  SISSA, Trieste - http://stefano.baroni.me,
> stefanobaroni (Skype)
>
> If the prediction that an airplane can stay up depends on the
> difference between Riemann and Lebesgue integration, I don’t want to
> fly in it [Richard W. Hammings]
>
>
>
>> On 20 Sep 2020, at 10:42, Mohad Abbasnejad
>> <mohaddeseh.abbasnejad at gmail.com> wrote:
>>
>> Hello Dear QE users
>> I am studying the effect of pressure on the frequencies.
>> In the experimental article, the pressure on the solid has been
>> reported to be 7 kbar.
>>
>> When I put this pressure (7 kbar) on my structure and let it relax,
>> the final pressure is calculated to be 6.57 kbar as the following.
>> Therefore it is not exactly 7 kbar.
>>
>> Computing stress (Cartesian axis) and pressure
>>
>>           total   stress  (Ry/bohr**3)                   (kbar)
>> P=    6.57
>>    0.00004467   0.00000000  -0.00000000          6.57      0.00     -0.00
>>    0.00000000   0.00004467  -0.00000000          0.00      6.57     -0.00
>>   -0.00000000  -0.00000000   0.00004467         -0.00     -0.00      6.57
>>
>>
>> MY QUESTION: Which pressure should I report on my paper;  7 kbar or
>> 6.57 kbar?
>>
>>
>> Any comments would be appreciated.
>>
>> Best regards
>> Mohaddeseh
>>
>>
>> --
>> ---------------------------------------------------------
>> Mohaddeseh Abbasnejad,
>> Assistant Professor of Physics,
>> Faculty of Physics,
>> Shahid Bahonar University of Kerman,
>> Kerman, Iran
>> P.O. Box 76169-133
>> Tel: +98 34 31322199
>> Fax: +98 34 33257434
>> Cellphone: +98 917 731 7514
>> E-Mail:     mohaddeseh.abbasnejad at gmail.com
>> <mailto:mohaddeseh.abbasnejad at gmail.com>
>> Website:  academicstaff.uk.ac.ir/moabbasnejad
>> <http://academicstaff.uk.ac.ir/moabbasnejad>
>> ---------------------------------------------------------
>>
>> _______________________________________________
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GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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I-00015 - Monterotondo Scalo (RM)
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E-mail: <giuseppe.mattioli at ism.cnr.it>

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