Thanks very much! On Mon, Nov 2, 2015 at 1:03 AM, Giovanni Cantele < [email protected]> wrote:
> > 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 > > > 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 > > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum >
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