[Wien] query for elastic constants

[Laurence Marks]

If I understand you correctly, your system is lower in energy for a
slightly smaller lattice parameter. This is not unusual, and depends upon
what functional you use. It is standard to calculate using the cell
parameters that minimize the dft energy.

Is this right? What is the relevance of "right"? Doing phonons for a non
dft-equilibrium cell is obvious GIGO. Beyond that to band etc there is no
"right".

_____
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Györgyi
www.numis.northwestern.edu

On Fri, Sep 17, 2021, 06:22 fatima DFT <fatimadft5 at gmail.com> wrote:

> I want to extend my question for band, doss, optical properties as well.
>
> One important thing is that the total energy is more negative for the
> original system by 0.65 eV when I apply 2.5% compressive strain and 2.8 eV
> when I apply 5% compressive strain.
>
> Thanks
>
>
> On Fri, Sep 17, 2021 at 3:33 PM fatima DFT <fatimadft5 at gmail.com> wrote:
>
>> Dear All,
>>
>> I am dealing with a cubic 3D perovskite system.
>> With its original lattice parameters, the system shows negative
>> frequencies.
>> At some 1% lattice strain, the system becomes dynamically stable (no +ve
>> frequency).
>>
>> My question is: Should I calculate elastic constant at the lattice
>> parameters where the system is dynamically stable or should I consider the
>> case with its original lattice parameters (fully optimized geometry with no
>> strain)?
>>
>>
>> Thank you
>> Fatima
>>
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