general question on calculating metals using cp2k
Jun
chen... at gmail.com
Thu Nov 3 10:34:53 UTC 2011
Thanks, Carlo.
Yes, I want to do slab calculations. The properties I am interested in
are, for example, adsorption energies of some atoms or molecules, work
function, DOS et al. For start, I guess the thickness of four layers
should be enough, I mean for Pt(111). What I am not so sure is the xy
dimensions. Would MxM, say M=5, be enough? I read some discussions on
the magnetic state of Ni that Ni slab of M=6 and 6 layers is necessary
to get a reasonable spin state. I hope it is less demanding for non-
magnetic metals like Pt.
Cheers,
Jun
On Nov 3, 8:53 am, carlo antonio pignedoli <c.pig... at gmail.com>
wrote:
> Dear Jun,
> regarding the size of the cell, it depends on which property of the
> system you would like to reproduce.
> There is a simple rule:
> if your property is well converged with a k-point cacluation for a
> unit cell on a MxM regular grid not shifted (I mean
> including Gamma point..)
> then a supercell as big as MxM the unit cell will give you "exactly"
> the same results.
>
> Of course overriding symmetries could bring the MxM system to a
> geomoetry not compatible
> with the unit cell (this does not mean that the result is wrong...)
> that's in part why I was saying "exactly".
>
> If you are interested in slab calculations, no k-points in the
> direction perpendicular to the slab surface,
> then the thickness of the slab, again, depends "solely" on the
> particular properties of the system that you
> would like to reproduce.
>
> For the behavior of the optimization algorithms i let somebody more
> expert to reply.
>
> Ciao
>
> Carlo
>
>
>
>
>
>
>
> On Wed, Nov 2, 2011 at 6:35 PM, Jun <chen... at gmail.com> wrote:
> > Hi,
>
> > I intend to run some calculations on metals. I am wondering if experts
> > could give me some ideas on the performance of cp2k. For example, to
> > model a metal surface, say Pt(111), what size of the system is big
> > enough for compensating the lack of k-point sampling? Usually, how
> > many iterations are needed to reach SCF convergence? How long it
> > roughly takes for each SCF step? How slow is the matrix
> > diagonalisation compared to OT? ...
>
> > It would be nice if someone shows me an input example for metals. I
> > know there was one given by Prof. Hutter about two years ago. Any up-
> > to-date one?
>
> > Thanks a lot,
>
> > Jun
>
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