[Wien] a note on lattice parameter optimization

[Laurence Marks]

Please think about the following questions:
1) Why is your number for the band gap "wrong", whereas what someone else
calculated with HSE is "right"?
2) What is the purpose of optimising internal and cell parameters?
3) Are the cell and internal parameters of PBEsol the same as what they
should be with mBJ? What does "should be" mean here?

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

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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