[Wien] accuracy test for RKMAX

[Stefaan Cottenier]

As you have Castep experience: RKmax in wien2k plays the same role as  
Ecut in Castep. What you have done are basically two identical  
calculations. Get :VOL for each case and plot :ENE versus :VOL to see  
how the curves look like (they predict the ground state volume, which  
Castep can find in a more automatic way by reducing the stress tensor  
to zero). Check also :DIS for each case (should be close to zero in  
case of good convergence, which is perhaps not true for your  
calculations).

Stefaan



Quoting santhy kathirvelu <k_santhy79 at yahoo.co.in>:

> Dear Schwarz,
>     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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-- 
Stefaan Cottenier
Instituut voor Kern- en Stralingsfysica
K.U.Leuven
Celestijnenlaan 200 D
B-3001 Leuven (Belgium)

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fax: + 32 16 32 79 85
e-mail: stefaan.cottenier at fys.kuleuven.be


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