[Pw_forum] atomic layers

[Giovanni Cantele]

> 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 <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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