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

[shamik chakrabarti]

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
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