[Wien] accuracy test for RKMAX

[Peter Blaha]

Hi,

I hope it is clear that you CANNOT use min_lapw for your bcc Ti example.

With respect to the volume optimization, I don't see anything bad.

Specifying RKMAX does not fix RKMAX to this value, it just guarantees 
that it does not get bigger than what you specified, but when changing 
the lattice parameter, it is natural that RKMAX changes.

You shoulds add a few more negative volumes (-9 -12 maybe -15) and then 
plot the results because it seems the minimum is near -6. When you get a 
nice parabola it seems ok, if not it may happen because of too low RKMAX 
(gotro 7.5, 8, up to 9) or to few k-points (100 is very little).

>   I am a new user of wien2k.  I had gone through the FAQ and L.D. Marks 
> notes for optimization.  I started with small system like Ti-BCC.  
> Before going to mini_lapw,  I tried the accuracy test as same as given 
> in the site http://www.wien2k.at/events/ws2006/Exercises.pdf.
>  
> I gave lattice parameter= 3.294A°, RMT=2.5(default), RKMAX=7(default), 
> k-point=1000 and Gmax=12(default) for Ti-BCC system.  I tried the same 
> step in the above site,
> STEP 1: run x optimize and generate 5 structures (-6, -3, 0, 3, 6 % 
> volume change)
> STEP2: edit “optimize.job”.
> STEP3: run optimize.job and plot the results. 
> I got
> SCF File          RKM               Energy
> Vol -6.0.scf      *6.93                 -1707.621717*
> Vol -3.0.scf      6.85                 -1707.621662
> Vol 0.0.scf       6.79                 -1707.621239
> Vol 3.0.scf       6.72                 -1707.619926
> Vol 6.0.scf       6.65                 -1707.618133
>  
> Energy is high when RKM is 6.93.   Since I changed RKMAX=6.93 in Ti.in1 
> file and I didn’t change any other parameter.  I repeated those 3 steps. 
> I got
>  
> SCF File          RKM               Energy
> Vol -6.0.scf      *6.93                 -1707.620994*
> Vol -3.0.scf      6.85                 -1707.620941
> Vol 0.0.scf       6.79                 -1707.620476
> Vol 3.0.scf       6.72                 -1707.619422
> Vol 6.0.scf       6.65                 -1707.617423
>  
> Here I observed that even though same RKMAX (=6.93) gives different 
> energy.  And I couldn’t  keep RKMAX as constant.  Since, during SCF 
> calculation it changes.
>  
> Sorry I took more of your time.  I have some experience to handle CASTEP 
> (in windows mode).  But I couldn't  correlate things in WIEN2k. 
>  
> It will be really helpful,  if you tell, how to do the accuracy test for 
> RKMAX.
>  
> Thanks in advance.
>  
> Santhy Jaiker
>  
> 
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