[Pw_forum] slab

[Axel Kohlmeyer]

On 11/29/08, fereydoon khazali <frnkhzi at yahoo.com> wrote:
> Dear All
> Is this input file correct for 5-layer slab of Ag(001)? vacuum thickness
> about 8.18 ang. & surface geometry is (2*2)

dear fereydoon,

please note that you are asking a not overly smart question:
a) if you care whether your input is syntactically correct, you
   can just run pw.x (well, you didn't even state that it was for pw.x)
   on it, and see if it gives the correct result.

b) if you care whether the output is acceptable, you have to verify
  this for yourself as well. if you want to publish this in a paper, do
  you think "some guy on the pw_forum mailing list wrote this is ok"
  is a good justification of the choice of input?

so while everybody here understands, that it is not always easy
to trust your own choice of parameters, there is no substitute for
teaching yourself how to find out. there are many examples in the
literature (including text books) on how to do this kind of calculation
and perhaps you should start with a very simple system that has
been studied a lot and is thus well documented, so you can check
the impact of your choices of parameters. not only will this solve
the currently pending question, but all similar ones in the future.
if you give this a little bit of thought, you'll understand that this
will be a much more reliable way than doing a poll amongst forum
members whether an input is good or bad.

for example, the fact, that you write to have an oxygen attached to your
surface makes all my neck hairs stand up and remind me of all
the problems one can have with the spin states of molecular oxygen.
...and thus i would not trust anything without careful testing (it may
be harmless, but i never studied this kind of system).

cheers,
   axel.

[...]
>
> thanks
> fereydoon Kh.


-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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If you make something idiot-proof, the universe creates a better idiot.