[Wien] a note on lattice parameter optimization

[Laurence Marks]

Inlined, please think:

On Feb 8, 2018 7:08 AM, "Dr. K. C. Bhamu" <kcbhamu85 at 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" <kcbhamu85 at 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, <tran at 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 <kcbhamu85 at gmail.com>
>> Reply-To: A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.
>> at>
>> To: A Mailing list for WIEN2k users <Wien at 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, <tran at 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 <kcbhamu85 at gmail.com>
>>            Reply-To: A Mailing list for WIEN2k users <
>> wien at zeus.theochem.tuwien.ac.at>
>>            To: A Mailing list for WIEN2k users <
>> Wien at 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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