[Wannier] wannier90 + vasp initial projections parallelism

[Aron Szabo]

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