<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On 31 Oct 2015, at 03:35, Safa Alzaim <<a href="mailto:safa.alzaim@gmail.com" class="">safa.alzaim@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><p class="">Dear All,</p><p id="yui_3_14_1_1_1446258320002_1789" class="">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? </p><p id="yui_3_14_1_1_1446258320002_1789" class="">Thanks!</p><p id="yui_3_14_1_1_1446258320002_1789" class="">Safa Alzaim</p>
<br class=""><br class=""></div>
_______________________________________________<br class="">Pw_forum mailing list<br class=""><a href="mailto:Pw_forum@pwscf.org" class="">Pw_forum@pwscf.org</a><br class="">http://pwscf.org/mailman/listinfo/pw_forum</div></blockquote></div><br class=""><div class=""><br class=""></div><div class="">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.</div><div class=""><br class=""></div><div class="">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 .</div><div class=""><br class=""></div><div class="">For various thickness materials, a1_surf and a2_surf are the same, whereas the card ATOMIC_POSITIONS and the length of a3_surf change.</div><div class=""><br class=""></div><div class="">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, <a href="http://people.sissa.it/~degironc/2011/tutorial_surface.pdf" class="">http://people.sissa.it/~degironc/2011/tutorial_surface.pdf</a></div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Giovanni</div><br class=""><br class=""><div apple-content-edited="true" class="">
-- <br class=""><br class="">Giovanni Cantele, PhD<br class="">CNR-SPIN<br class="">c/o Dipartimento di Fisica<br class="">Universita' di Napoli "Federico II"<br class="">Complesso Universitario M. S. Angelo - Ed. 6<br class="">Via Cintia, I-80126, Napoli, Italy<br class="">e-mail: <a href="mailto:giovanni.cantele@spin.cnr.it" class="">giovanni.cantele@spin.cnr.it</a><br class="">Phone: +39 081 676910<br class="">Skype contact: giocan74<br class=""><br class="">ResearcherID: <a href="http://www.researcherid.com/rid/A-1951-2009" class="">http://www.researcherid.com/rid/A-1951-2009</a><br class="">Web page: <a href="http://people.na.infn.it/~cantele" class="">http://people.na.infn.it/~cantele</a><br class="">
</div>
<br class=""></body></html>