[CP2K:3585] Re: general question on calculating metals using cp2k

carlo antonio pignedoli c.pig... at gmail.com
Thu Nov 3 11:12:02 UTC 2011


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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