<div dir="ltr">Dear Marcos, please review your CELL_PARAMETERS tag..!! I thing that there are some mistakes... you are using a square 2D lattice and not a hexagonal one.<div><br></div><div>Best</div><div><br></div><div>PhD. Arles V. Gil Rebaza</div>
<div>Instituto de Física La Plata</div><div>La Plata - Argentina</div></div><div class="gmail_extra"><br><br><div class="gmail_quote">2014-06-05 21:40 GMT-03:00 Marcos Veríssimo Alves <span dir="ltr"><<a href="mailto:marcos.verissimo.alves@gmail.com" target="_blank">marcos.verissimo.alves@gmail.com</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hi all,<div><br></div><div>I am trying to perform a cell optimization for graphene in which I would like to fix the atomic positions so as to have arbitrary bond lengths, and see what happens to the in-plane cell vectors. Thus I would like to keep the atomic positions fixed and let the in-plane cell vectors change.</div>
<div><br></div><div>I am using vc-relax with cell_dofree="2dxy" and I am (theoretically) fixing atomic positions (specified in Angstrom) with "0 0 0" after the cartesian coordinates. The problem is, the coordinates do not remain fixed during the cell optimization:</div>
<div><br></div><div><div>ATOMIC_POSITIONS (angstrom)</div><div>C 0.000000000 0.000000000 7.000000000 0 0 0</div><div>C 1.508583432 0.000000000 7.000000000 0 0 0</div><div>--</div><div>
ATOMIC_POSITIONS (angstrom)</div>
<div>C 0.000000000 0.000000000 7.000000000 0 0 0</div><div>C 1.553137965 0.000000000 7.000000000 0 0 0</div><div>--</div><div>ATOMIC_POSITIONS (angstrom)</div><div>C 0.000000000 0.000000000 7.000000000 0 0 0</div>
<div>C 1.583982256 0.000000000 7.000000000 0 0 0</div><div>--</div><div>ATOMIC_POSITIONS (angstrom)</div><div>C 0.000000000 0.000000000 7.000000000 0 0 0</div><div>C 1.592677072 0.000000000 7.000000000 0 0 0</div>
<div>--</div><div>ATOMIC_POSITIONS (angstrom)</div><div>C 0.000000000 0.000000000 7.000000000 0 0 0</div><div>C 1.597484048 0.000000000 7.000000000 0 0 0</div><div>--</div><div>ATOMIC_POSITIONS (angstrom)</div>
<div>C 0.000000000 0.000000000 7.000000000 0 0 0</div><div>C 1.599092143 0.000000000 7.000000000 0 0 0</div><div>--</div><div>ATOMIC_POSITIONS (angstrom)</div><div>C 0.000000000 0.000000000 7.000000000 0 0 0</div>
<div>C 1.598936919 0.000000000 7.000000000 0 0 0</div><div>--</div><div>ATOMIC_POSITIONS (angstrom)</div><div>C 0.000000000 0.000000000 7.000000000 0 0 0</div><div>C 1.598936919 0.000000000 7.000000000 0 0 0</div>
</div><div><br></div><div>My input is as follows:</div><div><br></div><div><div>&control</div><div> calculation='vc-relax'</div><div> restart_mode='from_scratch',</div><div> prefix='graphene',</div>
<div> pseudo_dir = '/home/mverissi/pseudos_espresso',</div><div> outdir='./'</div><div>/</div><div>&system</div><div> ibrav=0,</div><div> celldm(1)=4.073139044,</div><div> nat=2,</div><div>
ntyp=1,</div><div> nspin = 1, </div><div> ecutwfc = 28.0, </div><div> ecutrho = 252.0,</div><div> occupations='smearing', </div><div> smearing='methfessel-paxton', </div><div> degauss=0.001,</div>
<div> nbnd=10,</div><div>/</div><div>&electrons</div><div> conv_thr = 1.0e-9,</div><div> mixing_beta = 0.7 </div><div>/</div><div>&ions</div><div> ion_dynamics='bfgs'</div><div>/</div><div>&cell</div>
<div> cell_dynamics = 'bfgs',</div><div> cell_dofree = '2Dxy',</div><div>/</div><div>ATOMIC_SPECIES</div><div>C 12.0107 C.pbe-rrkjus.UPF</div><div>ATOMIC_POSITIONS {angstrom}</div><div>C 0.0 0.0 7.0 0 0 0 </div>
<div>C 1.42 0.0 7.0 0 0 0</div><div>K_POINTS {automatic}</div><div> 24 24 1 0 0 0</div><div>CELL_PARAMETERS {alat}</div><div> 0.866025404 0.5 0.0 </div><div> 0.866025404 -0.5 0.0 </div>
<div> 0.000000000 0.0 6.0</div></div><div><br></div><div>Am I making some silly mistake here? The version of Espresso in use is 5.0.2. Sorry if this has already come up, but I couldn't find anything similar to my problem.</div>
<div><br></div><div>Best regards,</div><div><br></div><div>Marcos</div></div>
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