[QE-users] Inconsistency of vc-relax output file

[Bharat Thapa]

On Mon, 8 Jul 2019 at 9:15 pm, Bharat Thapa <bhathapa at gmail.com> wrote:

> Dear Paolo,
>
> Sorry for the late reply, however, I am wondering in this case, how do I
> calculate the vc-relaxed lattice parameter? If it were cubic I would have
> multiplied the output CELL_PARAMETER with the lattice and divided by 0.5.
> But, as it is hexagonal (input) how do I figure out the relaxed lattice
> parameters? Also, I want to know if the symmetry (hexagonal) has been lost.
> How do I know the output file retains the input symmetry? The way I do is
> by looking the the CELL_PARAMETER. But in this case the output
> CELL_PARAMETER is not exactly representing that of ibrav= 4 but is somewhat
> closer.
> Please enlighten me on this; I am struggling a lot.
>
> Thank you!
>
>
> *Bharat Thapa*
>
>
> On Mon, Mar 25, 2019 at 7:27 AM Paolo Giannozzi <p.giannozzi at gmail.com>
> wrote:
>
>> Is the problem here the loss of the original symmetry of the lattice? if
>> hexagonal symmetry was present in the starting structure, it isn't lost at
>> the end (apart from pathological or unfortunate cases). If hexagonal
>> symmetry was not present in the starting structure, the final lattice may
>> no longer be hexagonal
>>
>> Paolo
>>
>>
>> On Sat, Mar 23, 2019 at 7:05 AM Bharat Thapa <bhathapa at gmail.com> wrote:
>>
>>> Dear developer,
>>>
>>>
>>>
>>> I have vc-relaxed Hf7O8N4 (hafnium oxynitride) assuming the crystal to
>>> be rhombohedra with a=b, alpha=beta=90 deg, and gamma=120 deg. So, I used
>>> ibrav=4 and gave A,B,C, cosAB, cosAC and cosBC values. Part of the input
>>> looks as follows:
>>>
>>>
>>>
>>> *&system*
>>>
>>> *    ibrav=  4                           *
>>>
>>> *    A=9.4851, B=9.4851, C=8.7867, cosAB=-0.5, cosAC=0.0, cosBC=0.0*
>>>
>>> *    nat=19  , ntyp= 3,*
>>>
>>> *    ecutwfc =70, ecutrho= 840, *
>>>
>>> *    occupations= 'fixed', *
>>>
>>> *    nbnd= 100 *
>>>
>>>
>>>
>>> The vc-relax ran successfully and I got the following output:
>>>
>>>
>>>
>>> *Final enthalpy =   -5322.7186767755 Ry*
>>>
>>> *Begin final coordinates*
>>>
>>> *     new unit-cell volume =   1536.19292 a.u.^3 (   227.64030 Ang^3 )*
>>>
>>>
>>>
>>> *CELL_PARAMETERS (alat= 17.92424134)*
>>>
>>> *   0.638651125   0.103631841  -0.047929083*
>>>
>>> *  -0.235833337   0.630643088  -0.049740867*
>>>
>>> *  -0.043220738  -0.085864416   0.635634338*
>>>
>>>
>>>
>>> Here, the output cell_parameter values are not consistent with the
>>> input. I assumed it as ibrav=4 (hex or rhombohedra), but if I use the
>>> output cell_parameter and calculated the final value (using the vector
>>> formulas for ibrav=4 from pw.x documentation) for lattice constant ‘a’, I
>>> will get different values from different vectors. So, my question is how do
>>> we analyse such a system in which we give certain crystal structure as an
>>> input and the vc-relax runs successfully (*does not crash*) and give an
>>> output which isn’t consistent with the input crystal system? Can I accept
>>> the results and carry on further because the vc-relax did not crash meaning
>>> that everything is fine?
>>>
>>>
>>>
>>> Please help me in this regard.
>>>
>>>
>>>
>>> Kind regards,
>>>
>>>
>>>
>>> Bharat Thapa
>>>
>>> PhD student
>>>
>>> UNSW
>>> _______________________________________________
>>> 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
>>
>> _______________________________________________
>> users mailing list
>> users at lists.quantum-espresso.org
>> https://lists.quantum-espresso.org/mailman/listinfo/users
>
> --
*Bharat Thapa*
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20190712/c99572c8/attachment.html>