[Wien] Requesting gentle clarification on OMP_NUM_THREADS, run_lapw, volume optimisation and wien2k update.

[Peter Blaha]

In addition to what L. Marks has already said:

A unit cell with 216 atoms should be run in mpi parallel mode. You won't 
have too many k-points probably, in particularly when doing position 
optimization.

About OMP Laurence Marks has already answered. The Intel mkl does not 
scale to higher OMP numbers. But: Test it out yourself. Set 
OMP_NUM_TREADS to 1 and run one iteration. Check the dayfile how long it 
takes. Set it to 2,4,8,16 and check the timing .... You should see that 
lapw0 will benefit when you set it to 64 (for your 216 atom cell), but 
unfortunately not much speedup in lapw1/2 anymore.

Update of WIEN2k: You should install wien2k into a new directory, thus 
you do not destroy the old installation. In addition, there is a "copy" 
function in siteconfig which would copy the old settings to the new 
installation. It is briefly described on the download page .and in the 
(new !) usersguide as well as in the "update" site of wien2k.

Updating is strongly recommended since the new init_lapw has some 
automatic precision settings and you won't run your supercell with 1000 
k-points .....

Volume optimization for high vacancy concentration is ok. What you read 
in the UG concerns the stress tensor, which is only NREL.

Hf-4f: No, these are core/semicore states. You don't need onsite-hybrid 
or LDA+U. However, depending on your RMTs you may be able to put them 
into the core by specifying a charge criterium instead of an energy 
(like   init -ecut 0.999)


> I have some general queries and it would be great if you can kindly 
> provide me your feedback.
>
>
>
>  1. I have 64 CPU (32 x 2) and more than 9 TB space and the system is
>     dedicated entirely to do simulations on DFT. I was thinking to set
>     the OMP_NUM_THREADS at 40 or 50 (even higher) to use the maximum
>     potential of the computer. But in the guidebook, it is recommended
>     that I do not set it higher than 8. May I please the reason for
>     this recommendation?
>
>  2. Is there a code to run_lapw continuously till it reaches the
>     convergence and not start it again after 40 cycles?
>
>  3. If I do a volume optimization for a single unit cell and then I
>     create a supercell of the optimized structure. Does the supercell
>     remains in optimized volume condition? Or it is recommended that I
>     do a volume optimization for the supercell as well. Further is
>     WIEN2k a reliable platform for volume optimization of HfO as in
>     the guidebook on page 87 it mentions “The accuracy is thus limited
>     to first and second row elements (maybe early 3d elements) and in
>     particular for the 5d series and above, large errors may occur due
>     to the neglect of (scalar-) relativistic corrections.”
>
>  4. Lastly, as it says on the website that it is highly recommended to
>     update the WIEN2K version, I am unable to find the manual where I
>     can follow the instructions to update the version. As I have not
>     done any installation of WIEN2K (my past colleague installed the
>     present version), I am worried that while upgrading I may commit
>     some mistake. A guideline on updating would have been very helpful.
>
> Looking forward to your kind feedback.
>
> Thank you in advance.
>
> With warm regards,
>
> Pranjal
>
>
>
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-- 
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Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-158801165300
Email:peter.blaha at tuwien.ac.at           
WWW:http://www.imc.tuwien.ac.at       WIEN2k:http://www.wien2k.at
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