<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi, if you want to study a nanowire, I do not see the reason why to optimise the unit cell along x and y directions.<div class="">Either freeze these two degrees of freedom in vc-relax or, much simpler, change c parameter (lattice parameter along the z direction)</div><div class="">and evaluate E(c) (total energy as a function of c). A parabolic fit will help you in finding the lowest energy configuration.</div><div class=""><br class=""></div><div class="">Generally speaking, to establish whether the vacuum is enough, calculate in at least one case the property you are interested in for two different</div><div class="">values of the vacuum and see if any appreciable change is observed. Another check is that the band structure should be flat (no dispersion)</div><div class="">along x and y</div><div class=""><br class=""></div><div class="">Giovanni</div><div class=""><br class=""></div><div class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 29 Nov 2017, at 06:28, Anik Mondol <<a href="mailto:anikmondol1206@gmail.com" class="">anikmondol1206@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class=""><div class=""><div class="">Dear Users,<br class=""></div>I am doing a DFT calculation of GaN nanowires, While designing the nanowire (approximately 10 A diameter) , I had added around 10 A of vacuum on x and y direction. Now I have performed a vc-relax calculation before band calculation, the cell volume has shrunk . The vacuum has decreased . Now to make sure the results don't be affected by the identical replicas , at least how much vacuum is needed ? Now, that the vacuum has shrunk, will that impose any effect on results in this respects. I mean, How can I be sure this vacuum is enough?<br class=""><br class=""></div>Mondol Anik Kumar <br class=""></div>Bangladesh University of Engineering and Technology <br class=""></div>
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<div style="color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" 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=""><a href="mailto:giovanni.cantele@spin.cnr.it" class="">e-mail: giovanni.cantele@spin.cnr.it</a><br class="">Phone: +39 081 676910<br class="">Skype contact: giocan74<br class=""><br class="">ResearcherID: http://www.researcherid.com/rid/A-1951-2009<br class="">Web page: http://people.fisica.unina.it/~cantele<br class=""></div>
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