[Wien] Structure relaxation for WO3 with atomic insertion

[Peter Blaha]

As was mentioned before:

For cubic, all your atoms are on high symmetry positions with (by 
symmetry) fixed positions. (It is like a NaCl structure). The code tells 
you: Forces are not present and there is nothing to optimize.

So all you can do with this symmetry is a volume optimization, or you 
displace the atoms a bit from these high symetry positions, to allow for 
lower symmetry which gives forces and positions which can be optimized.

What I would do:

Cubic:
init -b -numk 100 -rkmax 6
x optimize
edit optimize.job and increase convergence to -ec 0.00001
./optimize.job
eplot -a default

Evenutally you have to repeat  x optimize in case that the minimum was 
not in the selected range.
This gives you a first estimate of the volume. The calculations are not 
well converged (k-mesh, RMT, rkmax), but it should suffice to give an 
estimate where approximately the minimum is. For the structure closest 
to the minimum run
x nn      and check the "Bond valence sum (BVS). These numbers should be 
close to chemical intuition (Li +1, O 2-,..)

Other symmetries:
init -b -numk 100 -rkmax 6
x optimize   and always do a VOLUME optimization first, option1)
edit optimize.job and activate optimization of internal positions 
SIMULTANEOSLY for each volume:  Change the run_lapw  line and add
-min -fc 1  (this is listed after the comment symbol (#) anyway.

If you want, you can then do a c/a optimization for the best volume.

Check all BVS for the relaxed structures.

Once you have a crude minimum for all 3 structures, start over with the 
minimum structures and
choose ONE (consistent) set of RMTs for all structures
initialize with "better parameters" (k-mesh, RKmax)
Do again  x optimize  (including -min for the non-cubic structures)

and compare these minimum with the previous (crude) solution (it should 
change only little) and compare the energies of the structures.

PS: If during the first optimization a nn-overlap, no reasonable step 
error occurs, use   reduce_rmt to reduce the RMTs and continue.


Am 14.06.2020 um 23:53 schrieb Israel Omar Perez Lopez:
>   I just want to study the effect of Li insertion in the optical 
> properties of WO3. But first I have to obtain the atomic positions and 
> lattice parameters after Li insertion in those three structures.
> 
> So, in particular, I would like to know the steps I have to follow to 
> obtain this information. Do I have to do force minimization and volume 
> optimization, simultaneously? Or should I do minimization first and then 
> volume optmization after? or viceversa? And how do I do this?
> 
> I would appreciate any information on how to proceed.
> 
> Best Regards
> 
> Dr. Israel Pérez
> 
> Institute of Engineering and Technology
> 
> Department of Physics and Mathematics,
> 
> Universidad Autónoma de Ciudad Juárez
> 
> Av. del Charro 450 Nte., Col. Partido Romero,
> 
> Ciudad Juárez, Juarez Chihuahua. Mexico C. P. 32310
> 
> Tel: +52 (656) 688 4887
> 
> 
> National Council of Science and Technology
> 
> Insurgentes Sur No. 1582,
> 
> Col. Crédito Constructor,  C.P. 03940
> 
> Del. Benito Juárez, México D. F.
> 
> ------------------------------------------------------------------------
> *From:* Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of 
> Laurence Marks <laurence.marks at gmail.com>
> *Sent:* Sunday, June 14, 2020 3:35 PM
> *To:* A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.at>
> *Subject:* Re: [Wien] Structure relaxation for WO3 with atomic insertion
> To repeat, in cubic all your atoms are at high symmetry sites so 
> internal relaxation is not possible. User error, the program is telling 
> you. Please think it through.
> 
> N.B., to compare at the end you will need to convert everything to the 
> smallest RMTs.
> 
> _____
> 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 <http://www.numis.northwestern.edu>
> 
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-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671