[Pw_forum] Lower limit of target pressure

[Paolo Giannozzi]

You already solved the "issue":  the variable-cell optimization is done
with the plane-wave basis set for the starting cell, while the last step is
done with the plane-wave basis set for the final cell. The two differ by a
little bit (unless the cutoff is so high to guarantee perfect convergence
in both cases). Search for "Pulay stress"in the literature.

Paolo

On Wed, Sep 28, 2016 at 9:42 AM, Subhodip Chatterjee <subhopcqc at gmail.com>
wrote:

> Dear Paolo,
>
> I want to add few more informations.
>
> After the vc-relax calculation, the magnitude of pressure is  -*0.02 kbar*
> .
>
> And what I mentioned in my last post (i.e. *3.61 kbar*) is the pressure
> after the final SCF calculation.
>
> It will be a big help if you can guide me to solve this issue.
>
> Best regards
> Subhodip
>
> On Mon, Sep 26, 2016 at 11:24 AM, Subhodip Chatterjee <subhopcqc at gmail.com
> > wrote:
>
>> INPUT
>>
>> *press = 0.001*
>> *press_conv_thr = 0.0001*
>>
>> OUTPUT
>> *P (kbar) = 3.61*
>>
>> Best regards
>> Subhodip
>>
>> On Sat, Sep 24, 2016 at 7:15 PM, Paolo Giannozzi <p.giannozzi at gmail.com>
>> wrote:
>>
>>> "A lot" = how much? the default tolerance on pressure convergence is 0.5
>>> KBar
>>>
>>>
>>> Paolo
>>>
>>> On Sat, Sep 24, 2016 at 8:39 AM, Subhodip Chatterjee <
>>> subhopcqc at gmail.com> wrote:
>>>
>>>> Dear PWSCF developers,
>>>>
>>>> Is there any restriction in the code for the "press" (target pressure)
>>>> input?
>>>>
>>>> I successfully get my vc-relax calculations converged to desired
>>>> pressure values as high as several terapascal, however, when I set a low
>>>> enough value, e.g. 1 bar (i.e. press = 0.001), the final pressure in the
>>>> output differs a lot!
>>>>
>>>> Best regards
>>>> Subhodip
>>>>
>>>> --
>>>> *Subhodip Chatterjee*
>>>>
>>>> *Senior Research Fellow*
>>>>
>>>> *Department of Chemistry*
>>>> *University of Calcutta*
>>>> *Kolkata, India*
>>>>
>>>> _______________________________________________
>>>> Pw_forum mailing list
>>>> Pw_forum at pwscf.org
>>>> http://pwscf.org/mailman/listinfo/pw_forum
>>>>
>>>
>>>
>>>
>>> --
>>> 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
>>>
>>>
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
>>> http://pwscf.org/mailman/listinfo/pw_forum
>>>
>>
>>
>>
>> --
>> *Subhodip Chatterjee*
>>
>> *Senior Research Fellow*
>>
>> *Department of Chemistry*
>> *University of Calcutta*
>> *Kolkata, India*
>>
>
>
>
> --
> *Subhodip Chatterjee*
>
> *Senior Research Fellow*
>
> *Department of Chemistry*
> *University of Calcutta*
> *Kolkata, India*
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>



-- 
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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