> On 31 Oct 2015, at 03:35, Safa Alzaim <[email protected]> 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 > > > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum
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: [email protected] 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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