[Pw_forum] atomic layers
Safa Alzaim
safa.alzaim at gmail.com
Thu Nov 5 02:30:04 CET 2015
Thanks very much!
On Mon, Nov 2, 2015 at 1:03 AM, Giovanni Cantele <
giovanni.cantele at spin.cnr.it> wrote:
>
> On 31 Oct 2015, at 03:35, Safa Alzaim <safa.alzaim at gmail.com> wrote:
>
> Dear All,
>
> In quantum espresso, how do we define X number of atomic layers, for
> example, for a surface vs a bulk calculation? In our System and Atomic
> Positions block, the unit cell is the same for various thicknesses of
> material, so how do we set the calculation differently for a surface rather
> than bulk?
>
> Thanks!
>
> Safa Alzaim
>
>
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>
>
> surface calculations are set up by defining a surface supercell. That
> means that you should : i) to identify the surface primitive cell, defined
> by two vectors a1_surf and a2_surf ; ii) to build a slab along the third
> direction (orthogonal to a1_surf and a2_surf), by replicating one or more
> bulk atomic layers (the number of independent layers does depend on the
> specific system) and by adding (when setting the length of the a3_surf
> layer) vacuum space so as to get rid of spurious interactions between
> periodic replicas of the slab.
>
> If the third direction is the non-periodic one, the k-point grid (against
> which convergence should be always checked!) will be in the form n x m x 1 .
>
> For various thickness materials, a1_surf and a2_surf are the same, whereas
> the card ATOMIC_POSITIONS and the length of a3_surf change.
>
> There are examples within espresso-x.y.z/PW/examples and lot of
> tutorials/documentation on the web. For example, just by googling "quantum
> espresso surface calculation how to” I found, among the many,
> http://people.sissa.it/~degironc/2011/tutorial_surface.pdf
>
>
> Giovanni
>
>
> --
>
> Giovanni Cantele, PhD
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> e-mail: giovanni.cantele at spin.cnr.it
> Phone: +39 081 676910
> Skype contact: giocan74
>
> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
> Web page: http://people.na.infn.it/~cantele
>
>
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