[Wien] query for elastic constants

[fatima DFT]

Dear Sir,
I understand your point.  I am using PBE functional.

I am still in doubt, which lattice parameter I should use for the rest of
the properties.
Thanks


On Fri, Sep 17, 2021 at 5:11 PM Laurence Marks <laurence.marks at gmail.com>
wrote:

> That means that the cubic phase is not stable at T=0 for the functional
> you have chosen. This may be correct or incorrect, it is not uncommon (e.g.
> SrTiO3 with PBE).
>
> _____
> 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, 06:37 fatima DFT <fatimadft5 at gmail.com> wrote:
>
>> Thanks Sir
>> No Sir!!!
>> I mean, the original system is lower in energy but the phonon band
>> structure has some soft modes.
>> When I apply a compressive strain, the soft mode disappears.
>> I am sorry if you found my previous query a bit confusing.
>>
>> Thanks
>> Fatima
>>
>>
>>
>> On Fri, Sep 17, 2021 at 5:01 PM Laurence Marks <laurence.marks at gmail.com>
>> wrote:
>>
>>> 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
>>>>>
>>>> _______________________________________________
>>>> Wien mailing list
>>>> Wien at zeus.theochem.tuwien.ac.at
>>>>
>>>> https://urldefense.com/v3/__http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien__;!!Dq0X2DkFhyF93HkjWTBQKhk!CU-q4QLnagFyEv62yxcAvl8Kfi5TLM-08F260z_aYMEY99K8U8ECAO3K3s3jWBg6hGRtqQ$
>>>> SEARCH the MAILING-LIST at:
>>>> https://urldefense.com/v3/__http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html__;!!Dq0X2DkFhyF93HkjWTBQKhk!CU-q4QLnagFyEv62yxcAvl8Kfi5TLM-08F260z_aYMEY99K8U8ECAO3K3s3jWBiYk8FZEA$
>>>>
>>> _______________________________________________
>>> Wien mailing list
>>> Wien at zeus.theochem.tuwien.ac.at
>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>> <https://urldefense.com/v3/__http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien__;!!Dq0X2DkFhyF93HkjWTBQKhk!Aiu01CYsxX-RFTblmnYIFxWaDSebRoYf8Zf5zW4wj-wJ01RWFttMHgnW4ZPulW1pW2XcjA$>
>>> SEARCH the MAILING-LIST at:
>>> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
>>> <https://urldefense.com/v3/__http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html__;!!Dq0X2DkFhyF93HkjWTBQKhk!Aiu01CYsxX-RFTblmnYIFxWaDSebRoYf8Zf5zW4wj-wJ01RWFttMHgnW4ZPulW2mwzz9EQ$>
>>>
>> _______________________________________________
>> Wien mailing list
>> Wien at zeus.theochem.tuwien.ac.at
>>
>> https://urldefense.com/v3/__http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien__;!!Dq0X2DkFhyF93HkjWTBQKhk!Aiu01CYsxX-RFTblmnYIFxWaDSebRoYf8Zf5zW4wj-wJ01RWFttMHgnW4ZPulW1pW2XcjA$
>> SEARCH the MAILING-LIST at:
>> https://urldefense.com/v3/__http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html__;!!Dq0X2DkFhyF93HkjWTBQKhk!Aiu01CYsxX-RFTblmnYIFxWaDSebRoYf8Zf5zW4wj-wJ01RWFttMHgnW4ZPulW2mwzz9EQ$
>>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> SEARCH the MAILING-LIST at:
> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20210917/40f6444c/attachment.htm>