Dear Zarah,<div><br></div><div>Have you ever considered that you may want the cell relaxation in this case? (vc-relax)</div><div>It will optimize the cell parameter in order to minimize the total energy. You'll see that the system might have lots of interactions.</div>
<div><br></div><div>If you want to explore defects in crystals or surfaces, relaxing the internal coordinates are essential since you are breaking the symmetry in some way: by having impurities; surface interaction; vacancy defects and etc. If it is the case you want to explore, you will need to use a supercell approach. Remember: crystals are built based on symmetry rules. </div>
<div><br></div><div>If you are really curious, you might try to change the cell symmetry just to observe how the internal coordinations behave (just increase z by 0.2). It may not converge, but you will see a lot interactions. </div>
<div><br></div><div>Best regards,</div><div><br></div><div>Filipe</div><div><br>On Friday, February 28, 2014, Zarah Baiyee <<a href="mailto:z.baiyee@gmail.com">z.baiyee@gmail.com</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr"><div class="gmail_quote"><div dir="ltr">Hi All, <div><br></div><div>I am a new user to Quantum Espresso, therefore this may be a bit trivial but I any help would be very welcome. </div><div><br></div><div>I am attempting a relax calculation using espresso version 5.0.2, for the geometry optimisation of a perovskite structure. For the input below, the calculation runs, however does not compute any forces and convergence without geometry optimisation to the original structure, with 0 bfgs steps. I am able to perform an expected relaxation if alter the initial atomic positions to asymmetric: (i.e.) an oxygen molecule from: O (0.500 0.5 0.0) to O(0.499 0.5 0.0). </div>
<div><br></div><div>Please may someone shed some light on to why this is the case, and if there is anything wrong with my input. </div><div><br></div><div>Thanks</div><div><br></div><div>Zarah</div><div><a href="javascript:_e(%7B%7D,'cvml','Zbaiyee@gmail.com');" target="_blank">Zbaiyee@gmail.com</a></div>
<div><br></div><div><div>&CONTROL</div><div> calculation = "relax",</div><div> prefix = "CO",</div><div> pseudo_dir = "/Users/zarahbaiyee/espresso-5.0.2/pseudo",</div><div> outdir = "/Users/zarahbaiyee/tmp",</div>
<div> forc_conv_thr = 1.0D-5</div><div>/</div><div>&SYSTEM</div><div> ibrav = 0,</div><div> nat = 5,</div><div> ntyp = 3,</div><div> ecutwfc = 60,</div><div> ecutrho = 420,</div><div>/</div><div>
&ELECTRONS</div><div> conv_thr = 1.D-7,</div><div> mixing_beta = 0.7D0,</div><div> electron_maxstep = 400</div><div>/</div><div>&IONS</div><div>/</div><div>CELL_PARAMETERS bohr</div><div> 7.60 0.0 0.0</div>
<div> 0.0 7.60 0.0</div><div> 0.0 0.0 7.60</div><div>ATOMIC_SPECIES</div><div> Ba 137.32 Ba.pbe-mt_fhi.UPF</div><div> Fe 55.84 Fe.pbe-mt_fhi.UPF</div><div> O 15.99 O.pbe-kjpaw.UPF</div><div>ATOMIC_POSITIONS {crystal}</div>
<div>Ba 0.000 0.0 0.0 0 0 0 </div><div>Fe 0.500 0.5 0.5</div><div>O 0.000 0.5 0.5</div><div>O 0.500 0.0 0.5</div><div>O 0.500 0.5 0.0<br></div><div>K_POINTS {automatic}</div><div>9 9 9 0 0 0</div></div>
<div><br></div></div></div></div>
</blockquote></div><br><br>-- <br><div dir="ltr">_________________________________________<br>Filipe Camargo Dalmatti Alves Lima<br>PhD Student<br>University of São Paulo, Physics Institute, Materials Physics Department, Nanomol Group, Brazil.<br>
Phones: (11) 3091-6881 (USP)<br> (11) 97408-2755 (Vivo)<br></div><br>