[Pw_forum] Pw_forum Digest, Vol 60, Issue 7

[Lorenzo Paulatto]

On Tue, Jun 5, 2012 at 10:06 AM, Sanjay D. Gupta
<guptasanjay.56 at gmail.com>wrote:

> I agree that this warning not harmful to my calculation, however we are
> getting only symmetry recognition problem, earlier i have performed SnO2 in
> rutile phase and pw.x gives correct symmetry while for RuO2 case it doesn't
> happen. If is there any problem in my input file or i am missing something
> please also suggest me.
> With Kind Regards
>
>
>
You should re-center your structure (i.e. shift all the atoms by a constant
vector) in order to avoid the fractional translation. This solution
requires a bit of work but if you can find a good center you can then
forget about it.

Another solution, which requires less work at the beginning but more in the
end, is to define your fft grid by hand in order to make the fractional
translation commensurate with it. See the keywords nr1,nr2,nr3 (all three
of them must be defined) and notice that the automatic size of the grid is
printed as e.g.:
     G cutoff =  150.5174  (  18355 G-vectors)     FFT grid: ( 25, 25, 72)
which would mean nr1=25, nr2=25, nr3=72. In your case, you need all of them
to be even, i.e. set nr1=28, nr2=28, nr3=72. Remember that: 1. you should
not make nr* smaller than the automatic ones; 2. nr* with large prime
factors like 13 usually do not work because of the FFT algorithm (or are
very inefficient).

The problem, in this latter case, is that every time you change the cutoff,
or the cell you need to remember to change nr1* accordingly or you will get
garbage.

bests
-- 
Lorenzo Paulatto IdR @ IMPMC/CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
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