[Wien] Structure optimization

Lukasz Plucinski pluto at physics.ucdavis.edu
Fri Jun 1 13:36:07 CEST 2018 

Dear Profs. Blaha and Marks,

Thank you for your comments, it helps.

I indeed made a mistake of starting with asymmetric slab - first I did 
Fe atom only on one side of MgO, relaxed it, and then added another Fe 
atom on the other side of MgO. When starting with symmetric Fe/MgO/Fe 
slab things behave as expected. I wanted to check if there is much 
difference between having Fe atom on one or on both sides of the slab.

I am still using iMac computer with i7-3770 and 16 GB of RAM (perhaps I 
should really move to the cluster...), and my new external hard drive 
was not formatted to see case sensitive file names (Mac operating system 
allows things like this!). This is why I had issues with case.inm and 
case.inM filenames but it is fixed now.

For now I am happy with structure relaxation results and I like how it 
is done with MSR1a. On iMac I cannot really do much more than 6-8 
monolayer slab (I want to calculate dense k-point mesh later), but I 
think it will be sufficient for my purpose (I am currently checking if 
there is much difference between different slab thicknesses).

Best,
Lukasz


On 6/1/2018 1:16 PM, Lukasz Plucinski wrote:
>
>
>
>
> -------- Forwarded Message --------
> Subject: 	Re: [Wien] Structure optimization
> Date: 	Sat, 19 May 2018 09:06:33 -0500
> From: 	Laurence Marks <L-marks at northwestern.edu>
> 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>
>
>
>
> It works...but (sorry Peter) it can be bad science. There are special 
> cases where it is appropriate, but it can also be very inappropriate.
>
> There is a long history of people fixing some atomic positions to bulk 
> positions when performing surface calculations. However, the strain 
> field of any surface decays exponentially in the selvedge layer, and 
> removing this can be very wrong. For instance, there are many known 
> cases where the surface induces a ferroelectric distortion which fixed 
> positions will prevent from happening. The rigorous method is to check 
> that the atomic positions in the center of the slab are "close enough" 
> to those in the bulk. If they are not then either the slab needs to be 
> thicker or there has been a surface induced phase transition.
>
> And, fixing positions for a surface /in general does not improve the 
> convergence/. If you are lucky it will, but not in general. The reason 
> (as I have mentioned before) is that the convergence scales with the 
> number and width of the eigenvalue clusters, not the number of 
> variables. If the convergence of Wien2k and other DFT codes scaled 
> with the number of density variables, the methods would be useless! 
> DFT is a useful method because it will typically converge in 10-100 
> scf iterations because there are only a few eigenvector clusters of 
> the dielectric response (in density only calculations) and the force 
> matrix (with PORT). MSR1a is typically efficient because the number 
> and width of the clusters of the general dielectric response with both 
> density and electronic terms included is smaller than the product of 
> the clusters for the electronic and atomic components.
>
> Sorry for being so pedantic...but rigor matters.
>
> On Sat, May 19, 2018 at 7:56 AM, Peter Blaha 
> <pblaha at theochem.tuwien.ac.at <mailto:pblaha at theochem.tuwien.ac.at>> 
> wrote:
>
>     > - How can I lock some atoms in position during structure optimization?
>
>     In case.inM  put the 1.0 values of x,y and/or z of the corresponding
>     atom (line) to 0.0.
>
>     It works well. We do it all the time....
>
>     >
>     > Best,
>     > Lukasz
>     >
>
>     -- 
>     --------------------------------------------------------------------------
>     Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
>     Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
>     Email: blaha at theochem.tuwien.ac.at
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> -- 
> 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> ; 
> Corrosion in 4D: MURI4D.numis.northwestern.edu 
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> Co-Editor, Acta Cryst A
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