[Pw_forum] graphene on BN calculation
Lorenzo Paulatto
paulatto at sissa.it
Wed Dec 16 18:22:28 CET 2009
Replying to message "[Pw_forum] graphene on BN calculation" from mohamed
sabri majdoub (16/12/09):
> I am not sure that I am doing it the right way. I am using 40 processors
> and I the calculations look very slow to me.
Well, it's a big system. You can speed it up by using tqr=.true.
(real-space augmentation charge). There is also an experimental real-space
algorithm, but I don't know how reliable it is at the moment (you can
contact baris _at_ sissa.it for additional info).
> tstress = .t.
there is no need to print the stress, and it takes time to compute (not
much)
> diagonalization = 'cg'
For better performance you should use the default (david). If you have
some problem with it, you should ask for help on the forum before falling
back to cg, which is non much more robust and quite a bit slower. Also,
diagonalization errors are most of the time input errors/bad atomic
positions.
> K_POINTS automatic
> 30 30 1 1 1 0
this is a huge number of k-points for such a cell, are you sure you need
all of them? Remember that every time you increase the cell size by N you
can reduce the number of k-points by the same factor. (e.g. a 2x2x2
super-cell only need on eighth of the k-points of the original cell).
Computation time scales linearly with the number of points, e.g. "10 10 1
1 1 0" will be about 9 times faster.
best regards
--
Lorenzo Paulatto
SISSA & DEMOCRITOS (Trieste)
phone: +39 040 3787 511
skype: paulatz
www: http://people.sissa.it/~paulatto/
*** save italian brains ***
http://saveitalianbrains.wordpress.com/
More information about the Pw_forum
mailing list