[Wien] a note on lattice parameter optimization

[tran at theochem.tuwien.ac.at]

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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