Dear Peter Sir,
Please have a look at my recent query.
Regards
Fatima
On Mon, Sep 27, 2021, 6:19 PM fatima DFT wrote:
> Dear Sir,
> Thank you very much for your reply.
> Sorry for the late response as I was doing phonon calculation with LDA.
>
> I found that with LDA, the system shows thermodyn
Dear Sir,
Thank you very much for your reply.
Sorry for the late response as I was doing phonon calculation with LDA.
I found that with LDA, the system shows thermodynamic stability, and that's
why I was getting all frequency positive at compressive strain when I was
using PBE.
Can I proceed with
The most fundamental procedure is to use the theoretically optimized
volume for all properties.
If the DFT result is very bad, sometimes one also used experimental
lattice parameters.
Phonons: There is nothing unusual about imaginary phonons in the
harmonic approximation for cubic perovskites.
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
wrote:
> That means that the cubic phase is not stable at T=0 for the functional
> you
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
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 M
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"
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 fa
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
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