[Wien] Large forces appeared when calculating total energy after structure optimization

[shamik chakrabarti]

Dear Prof. Blaha & Gavin,

                         Sorry to bother you again. I think I have done a
foolish job by starting with the command .....-i 160 as it will converge
just at the first or the second cycle without minimizing the forces.
I have taken into account spin polarization during structure optimization,
however, I have not taken into account GGA+U for structural optimization. I
have inserted the U after a converged SCF obtained with spin polarization &
with the optimized structure.

Looking forward to listen from you.

with regards,
Dear Prof. Blaha & Gavin,



On Sun, 7 Feb 2021 at 12:09, shamik chakrabarti <shamik15041981 at gmail.com>
wrote:

> Dear Prof. Blaha & Gavin,
>
>                                  I have checked the final energy obtained
> (during force minimization) & the energy obtained after an SCF by taking
> the optimized structure & it is found that the final energy obtained during
> the force minimization is less (more negative) than the energy obtained
> during SCF with optimized structure. It seems that that the iteration has
> found a local minimum. Hence, I have started the SCF again with a command
> runsp_lapw -dm -orb -NI -fc 1.0 -ec 0.0001 - cc 0.0001  -i 160 (previously
> the iteration has run for 80 iterations).
>
> Is it the correct way to approach it? Looking forward to hearing from you.
>
> with best regards,
>
> On Sat, 6 Feb 2021 at 22:58, Gavin Abo <gsabo at crimson.ua.edu> wrote:
>
>> It might also be worth mentioning that you may need to look into the
>> details of the structure that you are calculating.
>>
>> By that, I'm referring to how optimization of atomic coordinates does
>> not work on structures were there are no atoms in a free atomic position
>> and all atoms in the structure are in fixed atomic positions of the
>> spacegroup, like the example given for NaCl, as described in the
>> following five links.
>>
>> [1] Slide 36:
>>
>> http://www.wien2k.at/reg_user/textbooks/WIEN2k_lecture-notes_2013/WIEN2k-getting_started.pdf
>> [2]
>> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20232.html
>> [3]
>> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20213.html
>> [4]
>> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg02859.html
>> [5]
>> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg17074.html
>>
>> On 2/6/2021 9:40 AM, Peter Blaha wrote:
>> > All we can say is that you have done somewhere a mistake.
>> >
>> > It is important that you not just "describe" what you did, but list
>> > the actual commands.
>> >
>> > Did you use the same   runsp command during "optimization" ?
>> >
>> > Could it be that you restarted the final SCF from "scratch" ???
>> > In DFT+U you might have ended up in a different state when starting
>> > with dstart densities without *dmat* files.
>> >
>> > Compare your total energies of best optimization and the final SCF.
>> > Which one is lower ?
>> >
>> > Am 06.02.2021 um 12:47 schrieb shamik chakrabarti:
>> >> Dear Wien2k users,
>> >>                                  I have initially optimized an
>> >> orthorhombic crystal system structurally (simultaneous
>> >> optimization of a,b,c & coordinates & then optimization of
>> >> coordinates again by taking optimized lattice parameters). However,
>> >> after taking the optimized structure when I simulate the total energy
>> >> with converged SCF by running the command runsp_lapw -dm -orb -fc 1.0
>> >> -ec 0.0001 -cc 0.0001, I have found that large forces ~ 40 mRy/a.u.
>> >> appeared for few atoms.
>> >>
>> >> My queries are (a) why this happens? & (b) what is the remedy? (c)
>> >> whether DOS is reliable in this case?
>> >>
>> >> *However, the simulated voltage as calculated from the total energy
>> >> of the system has been matched with the experiment very well.
>> >> *
>> >>
>> >> Looking forward to hearing from you.
>> >>
>> >> with regards,
>> >> --
>> >> Dr. Shamik Chakrabarti
>> >> Research Fellow
>> >> Department of Physics
>> >> Indian Institute of Technology Patna
>> >> Bihta-801103
>> >> Patna
>> >> Bihar, India
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>>
>
>
> --
> Dr. Shamik Chakrabarti
> Research Fellow
> Department of Physics
> Indian Institute of Technology Patna
> Bihta-801103
> Patna
> Bihar, India
>


-- 
Dr. Shamik Chakrabarti
Research Fellow
Department of Physics
Indian Institute of Technology Patna
Bihta-801103
Patna
Bihar, India
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