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<p>Dear Li,</p>
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<p>I had the same issue back in the days.If you start really far from equilibrium it is usually hard to get the ground state, the way I solved it is by running a scf for a set of celldm(1) and looking either at forces, pressure or the total energy.</p>
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<p>Once the approximate value of celldm is found, I runned a relax calculation and than a vc-relax.</p>
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<p>Hope this will work for you as well,</p>
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<p>Cheers,</p>
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<p>Zack<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of jibiaoli <jibiaoli@foxmail.com><br>
<b>Sent:</b> Friday, November 23, 2018 10:32:11 AM<br>
<b>To:</b> users<br>
<b>Subject:</b> [QE-users] Unit Cell goes larger and larger in variable cell geometry optimization</font>
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<div>Dear QE users and developers,</div>
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<div>Recently I used vc-relax to optimize Se in the honeycomb structure, but the unit cell goes larger and larger without convergence. To me there must be something wrong with my calculations. Do you have any idea to get everything right?</div>
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<div>Best</div>
<div>Jibiao Li</div>
<div>Yangtze Normal University, China</div>
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<div> &CONTROL<br>
calculation = 'vc-relax' ,<br>
restart_mode = 'from_scratch' ,<br>
outdir = './' ,<br>
pseudo_dir = '/home/jibiaoli/pseudo/' ,<br>
prefix = 'Se_hc' ,<br>
disk_io = 'high' ,<br>
/<br>
&SYSTEM<br>
ibrav = 4,<br>
celldm(1) = 4.7126,<br>
celldm(3) = 8.41,<br>
nat = 2,<br>
ntyp = 1,<br>
ecutwfc = 41 ,<br>
ecutrho = 180 ,<br>
occupations = 'smearing' ,<br>
degauss = 0.05D0 ,<br>
smearing = 'methfessel-paxton' ,<br>
vdw_corr = 'grimme-d2' ,<br>
/<br>
&ELECTRONS<br>
mixing_beta = 0.3D0 ,<br>
diagonalization = 'david' ,<br>
/<br>
&IONS<br>
ion_dynamics = 'bfgs' ,<br>
/<br>
&CELL<br>
cell_dynamics = 'bfgs' ,<br>
cell_dofree = '2Dxy' ,<br>
/<br>
ATOMIC_SPECIES<br>
Se 78.96100 Se.pbe-van.UPF <br>
ATOMIC_POSITIONS angstrom <br>
Se 1.246899765 0.719897900 0.000000000 <br>
Se 0.000000000 0.000000000 0.000000000 0 0 0<br>
K_POINTS automatic <br>
9 9 1 0 0 0 <br>
<br>
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