general question on calculating metals using cp2k

Jun chen... at gmail.com
Thu Nov 3 13:27:21 CET 2011


Could anyone comment on the efficiency of cp2k on metals, for example,
a 5x5 Pt(111) slab of 4 layers (100 atoms)?

Thanks in advance!

Jun

On Nov 3, 11:12 am, carlo antonio pignedoli <c.pig... at gmail.com>
wrote:
> Dear Jun,
> yes you are right H saturation is standard for semiconducting and
> insulating systems,
> there is in the literature (I will have to find it) a discussion on the ability
> of H saturation in Au(111) (if I remember well) to reduce spurious interactions
> among surface states at the sides of the slab.
>
> Ciao
>
> Carlo
>
>
>
>
>
>
>
> On Thu, Nov 3, 2011 at 12:04 PM, Jun <chen... at gmail.com> wrote:
> > Thanks very much again for the prompt reply, Carlo.
>
> > I agree a thickness of 4 layers is a minimum. I hope the screening of
> > metals is strong enough to eliminate the interaction between two
> > surfaces. I know termination with H atoms to saturate surface dangling
> > bonds is often used for covalent solids with a band gap. Is this
> > necessary for metals?
>
> > I will definitely do some tests on the size of slab before I really
> > run the calculations.
>
> > Cheers,
> > Jun
>
> > On Nov 3, 10:43 am, carlo antonio pignedoli <c.pig... at gmail.com>
> > wrote:
> >> Dear Jun form the experience I have for systems I worked on,
> >> a slab 4 layer thick could be the minimum thickness for a first investigation,
> >> be careful that you would have, in such a thin slab, a spurious interaction
> >> among surface states.
> >> To reduce this, a "empirical" way is hydrogenation of one side of the slab.
>
> >> Dont' forget to consider the relevance of van der Waals corrections.
>
> >> Usually the smallest slab I consider in xy is in the order of 6x6
> >> compared to a primitve cell
> >> but this is just an indication and the result depend really on the
> >> particular system you are dealing with.
>
> >> Magnetic systems are always complex.. I have not enough experience on
> >> this to give
> >> you suggestions.
>
> >> Ciao
>
> >> Carlo
>
> >> On Thu, Nov 3, 2011 at 11:34 AM, Jun <chen... at gmail.com> wrote:
> >> > 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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