<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Feb 16, 2010, at 12:27 PM, Shyam Khambholja wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Dear all,</div>
<div> I am doing total energy calculation for a system having two atoms per unit cell. When doing it I am getting converged total energies upto lattice constant a=7 bohr. When doing calculation for higher values of a=8 bohr, I am getting following message.</div>
<div> </div>
<div>convergence not achieved.</div>
<div>end of calculation. </div>
<div> </div>
<div>and as a result, i am not getting value of total energy.</div>
<div>so, help me</div>
<div> </div>
<div>thanks in advance</div>
<div><br clear="all"><br>-- <br>Shyam G Khambholja<br>Reseach student,<br>Depratment of Physics,<br>Sardar Patel University </div><br></blockquote></div><br><div><br class="webkit-block-placeholder"></div><div>Convergence related issues might be found here:</div><div>
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div><a href="http://www.quantum-espresso.org/wiki/index.php/Frequently_Asked_Questions#Self-consistency_is_slow_or_does_not_converge_at_all">http://www.quantum-espresso.org/wiki/index.php/Frequently_Asked_Questions#Self-consistency_is_slow_or_does_not_converge_at_all</a></div><div><br></div><div>Also, please explore the user forum, I think there should be lots of convergence-related posts!<br class="Apple-interchange-newline"><br></div><div>What kind of system/crystal/whatever are you calculating? Usually scf is not expected to converge for ANY input file. Your input structure should be physically meaningful.</div><div><br></div><div>Why do you change the "lattice constant" by a large amount? This might be useful if you are considering an "isolated" molecule and want to check convergence with</div><div>respect to the vacuum space separating the periodic replica (in this case I would say 7 bohr is too small), but if you are trying to optimize the unit cell of some crystal,</div><div>usually you explore the total energy vs lattice constant by varying the latter by small amounts (your Delta a = 1 bohr means 14%!!!!).</div><div><br></div><div>Giovanni</div><div><br></div><div>--</div><div><br></div><div>Dr. Giovanni Cantele<br>Coherentia CNR-INFM and Dipartimento di Scienze Fisiche<br>Universita' di Napoli "Federico II"<br>Complesso Universitario di Monte S. Angelo - Ed. 6<br>Via Cintia, I-80126, Napoli, Italy<br>Phone: +39 081 676910<br>Fax: +39 081 676346<br>E-mail: <a href="mailto:giovanni.cantele@cnr.it">giovanni.cantele@cnr.it</a><br> <a href="mailto:giovanni.cantele@na.infn.it">giovanni.cantele@na.infn.it</a><br>Web: <a href="http://people.na.infn.it/~cantele">http://people.na.infn.it/~cantele</a><br>Research Group: <a href="http://www.nanomat.unina.it/">http://www.nanomat.unina.it</a><br>Skype contact: giocan74</div></span>
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