[Pw_forum] input for a polymer crystal

[Axel Kohlmeyer]

On Sat, Jan 10, 2009 at 10:12 PM, Jonas Baltrusaitis <jasius_1 at yahoo.com> wrote:
> I am trying to optimize a hydrogen bonded polymer crystal structure. I have experimental a,b,c and all three angles of the cell, as well as the point group. Also fractional coordinates
>
> what I don't have is an idea how to prepare an input. I read Doc/Input_pw closely and couldn't find how to utilize any of those (except atomic positions).
>
> CELL_PARAMETERS should accommodate those somwehow but it's only 3x3 matrix input in the manual instead. also, specifying ibrav, celldm, nat, ntyp and nbnd are not clear as it's nothing like a simple Al or Si structure. also, what do I put for K_POINTS? Gamma only?

if you have all you this information, ibrav, celldm, nat, ntyp are all defined.
CELL_PARAMETERS is only needed if you set ibrav=0. nbnd depends on
your pseudopotentials
and whether you use smearing or not. probably the default set by pw.x
is sufficient  and
you can probably get away with fixed occupations and gamma, but that
just needs to be
tested. there is a wealth of material on how to set up proper jobs
with pw.x and other codes,
also discussing convergence issues (which cannot be predefined) at:

http://www.quantum-espresso.org/wiki/index.php/Tutorials_and_Examples

perhaps you shoud study this more closely. if all these rather
elementary parameters
tell you nothing, than you should work on your understanding of the
methods you use
_before_ you use them for a production calculation...

cheers,
     axel.


>
> thanks for the help
>
> Jonas Baltrusaitis
> University of Iowa
>
>
>
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>



-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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