Dear Prof. Marks,

Thank you very much for the conceptual reply.

I am unable to answer the second point now but  please see for 1st and 3rd
point:

I agree that some time hybrid calculations may fail for some systems. May
you also want to point out that with element from high Z a -SO correction
is needed. But in some reputed papers (Nano. letters) it is mention that
-SO does not affect much for my system.


Regarding, PBESol: in two of PRB papers of Prof. Peter, it is mentioned
that PBESol and WC-GGA are better for optimization
"PhysRevB.79.155107.pdf", PHYSICAL REVIEW B 79, 085104 2009 . The same
trend I am getting where LDA is underestimating the lattice parameter
optimization and PBE is overestimating for a list of materials that I have
testes.

WC-GGA and PBESol are giving the optimized lattice parameters in the
vicinity of Exp lattice parameters (~0.01-~0.02 Ang reduced). So I used
PBESol with mBJ.

Yes, I also do agree that according to UG, LDA or PBE are good for mBJ but
as PBESol gave me well-optimized results so I used PBESol with mBJ.


So I am not able to find out the solution to my issue; Why the bandgap is
drastically reducing if I use "double relaxed structure":

1. relaxed>> 2. optimization of lattice parameter without relaxing>>> 3.
again relaxing the structure (using relaxed structure from step 1 and
optimized lattice parameter from step 2.).

I am sure the procedure used above seems wrong but I am not able to justify
the "double relaxation of the structure.


regards,

Bhamu







On Thu, Feb 8, 2018 at 6:48 PM, Laurence Marks <l-ma...@northwestern.edu>
wrote:

> Inlined, please think:
>
> On Feb 8, 2018 7:08 AM, "Dr. K. C. Bhamu" <kcbham...@gmail.com> wrote:
>
> Dear Prof. Marks,
>
> I believe I am having to understand about the mentioned  points:
>
>
> 1) Why is your number for the band gap "wrong", whereas what someone else
> calculated with HSE is "right"?
>
> Ans: Maybe you want to ask me why the band gap from my calculations should
> be fine instead of HSE. If so, then I shall mention that hybrid
> calculations are already a well know approach to predict the band gap of
> inorganic systems.
>
>
> Does that mean HSE is right?
>
>
> 2) What is the purpose of optimizing internal and cell parameters?
>
> Ans: To get the minimum forces on the system and by doing total
> optimization the system would be in the most stable ground state and can
> give accurate properties if the most suitable approach is applied!!
>
>
> Why?
>
>
> 3) Are the cell and internal parameters of PBEsol the same as what they
> should be with mBJ? What does "should be" mean here?
>
> Ans: Yes, structure file is same for PBESol and mBJ. According to me you
> wanted to ask me whether I have applied any changes in mBJ calculation,
> like relaxation (which is not possible and I did not apply).
> I just did PBESol scf >> save_lapw case_scf>>> one scf cycle>> save_lapw
> mbjx_grr >>> spacified the mBJ approach and finally mBJ scf.
>
> Why should a PBEsol refined structure be optimal for mBJ?
>
>
> regards
> Bhamu
>
>
> On Feb 8, 2018 3:41 AM, "Dr. K. C. Bhamu" <kcbham...@gmail.com> wrote:
>
> No, I said the calculated gal is ~0.3eV less then the reported gap: HSE.
>
>
> I tested this on more than 10 systems and in each case obsessed this band
> gap discrepancy.
>
> Regards
> Bhamu
>
> On Feb 8, 2018 3:05 PM, <t...@theochem.tuwien.ac.at> wrote:
>
>> A band gap of 0.3 eV is very small and a change of lattice constant may
>> be enough to close the band gap.
>>
>> On Thursday 2018-02-08 10:30, Dr. K. C. Bhamu wrote:
>>
>> Date: Thu, 8 Feb 2018 10:30:29
>>> From: Dr. K. C. Bhamu <kcbham...@gmail.com>
>>> Reply-To: A Mailing list for WIEN2k users <w...@zeus.theochem.tuwien.ac.
>>> at>
>>> To: A Mailing list for WIEN2k users <Wien@zeus.theochem.tuwien.ac.at>
>>> Subject: Re: [Wien] a note on lattice parameter optimization
>>>
>>> Yes, I used PBESol followed by mBJ.
>>>
>>> On Feb 8, 2018 2:28 PM, <t...@theochem.tuwien.ac.at> wrote:
>>>      Hi,
>>>
>>>      Did you use mBJ to calculate the band gap in both procedures?
>>>
>>>      FT
>>>
>>>      On Thursday 2018-02-08 09:35, Dr. K. C. Bhamu wrote:
>>>
>>>            Date: Thu, 8 Feb 2018 09:35:08
>>>            From: Dr. K. C. Bhamu <kcbham...@gmail.com>
>>>            Reply-To: A Mailing list for WIEN2k users <
>>> wien@zeus.theochem.tuwien.ac.at>
>>>            To: A Mailing list for WIEN2k users <
>>> Wien@zeus.theochem.tuwien.ac.at>
>>>            Subject: [Wien] a note on lattice parameter optimization
>>>
>>>            Hello,
>>>
>>>            Using experimental lattice parameters(a Ang), I optimized the
>>> structure with two options.
>>>
>>>            1. Directly optimized the structure without min_lapw ... and
>>> the optimized lattice parameters are in the vicinity of Exp a (~0.01 Ang
>>> accuracy) and the calculated band gap (from mBJ2) is in agreement with
>>> reported value ~0.3 eV less.
>>>
>>>            2. First relaxed the structure and then optimized this
>>> relaxed structure (without min_lapw ....). In this case the optimized
>>> lattice parameters are reduced by ~0.05 Ang and the band gap vanished or
>>> largely reduced.
>>>
>>>
>>>            Why is the second way of doing band structure not working?
>>>
>>>            I tested it on many systems. In some case system became metal
>>> and in some cases band gap largely reduced when  I used the fully relaxed
>>> structure for optimization.
>>>
>>>
>>>            Thanks,
>>>
>>>
>>>            Bhamu
>>>
>>>
>>>
>>>
>>>
>>>
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