[Wannier] wannier90 + vasp initial projections parallelism

[Aron Szabo]

Dear Nicola,

I meant to do separately the calculation of the overlaps (with the 
unmodified code. This part seemed to scale with the cpu-s, and it 
doesn't depend on the projections), and the calculations of the 
projections that could be "parallelized" by running vasp many times with 
selecting just a few projections in the input for each, and just 
concatenate the results (and change the band indices). That's how I do 
it now, and it works, but the overlaps are calculated in each case, 
while they are identical, and it takes a lot of time unnecessarily, 
making it impossible to go above a certain size (300 atoms approx.).

Anyway, my next question would have been that how is it done in quantum 
espresso. So thank you for your answer, I'm going to check whether I 
could do all my tasks with quantum espresso. It seems to be more 
practical in this respect then.

And thank you for your offer to meet in person. I will probably use the 
opportunity, and contact you in private to arrange the details.

Best regards,
Aron

On 01/13/2015 12:00 PM, Nicola Marzari wrote:
>
> Hi Aron,
>
>
> but without overlaps you won't have MLWFs? I guess you are just trying
> to do "poor man's Wannier" via projections?
>
> Still, might be worth trying quantum-espresso, since those calculations
> are parallelized. All plane wave codes are fairly similar, at the end...
>
> I'll be in ETHZ next week (wed/thu), so we could always catch up there.
>
>             nicola
>
>
> On 13/01/2015 11:55, Aron Szabo wrote:
>> Dear Wannier90 developers,
>>
>> I'm using vasp 5.3 and wannier90 2.0. I've noticed that the calculation
>> of the initial projections for the wannierization in vasp is sequential,
>> it doesn't speed up with the increasing number of cpu-s. For large
>> systems I'm calculating separately smaller sets of projections to
>> emulate some parallelism, but there is a huge overhead from calculating
>> the overlaps first in each case. It can take 1-2 days just to start
>> calculating the projections when I have 2-300 atoms (1-2000 bands). So
>> generating the projections can take more time than the actual
>> wannierization. If the calculation of the overlaps could be somehow
>> switched off, it would already solve this problem practically, because
>> then the calculation of the projections would scale nicely, and the
>> overlaps could be calculated in a separate run. I'm not good in fortran,
>> so I'm asking you whether it could be done maybe by just commenting out
>> a few lines somewhere either in vasp's or wannier90's code, and if so,
>> where is it exactly? I'm also interested if it is planned at all to
>> parallelize the wannierization sometimes in the future, or is the
>> problem itself something that's not possible to parallelize efficiently?
>>
>> Thanks in advance,
>> Aron Szabo
>> PhD student at IIS, ETH Zurich
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>