Dear QE users,<div><br></div><div>I am new to quantum espresso and was playing with a simple test case of variable cell relaxation. I created a virtual tetragonal MgO cell with c/a ratio as 1.4. I was expecting this ratio will become close to 1.4142 (cubic) after relaxation. However, I am getting values that are off this theoretical value. I tried to play with different threshold parameters but didn't see significant improvement. Did I miss an important parameter somewhere? I am pasting the input file. Thanks.</div>
<div><br></div><div>Regards, Wei</div><div>Wei Lai<br>Michigan State University<br>East Lansing, MI 48824
</div><div><br></div><div> &control</div><div> calculation = 'vc-relax',</div><div> restart_mode='from_scratch',</div><div> prefix='MgO',</div><div> tstress = .true.</div><div> tprnfor = .true.</div>
<div> pseudo_dir = '/home/espresso-4.3.2/pseudo/',</div><div> outdir='/home/wl2/tmp/'</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>nstep=100</div><div> /</div><div> &system </div>
<div> ibrav= 7, celldm(1) = 5.6298, celldm(3) = 1.4, nat= 2, ntyp= 2,</div><div> ecutwfc =30, input_dft='pw91'</div><div> /</div><div> &electrons</div><div> mixing_mode = 'plain'</div><div>
mixing_beta = 0.7 </div>
<div> conv_thr = 1.0d-8</div><div> /</div><div> &ions</div><div> ion_dynamics = 'bfgs'</div><div> trust_radius_ini=1.0d-1</div><div> trust_radius_max=1.0d-3</div><div> /</div><div> &cell</div><div>
<span class="Apple-tab-span" style="white-space:pre"> </span>cell_dynamics='bfgs'</div><div> /</div><div> ATOMIC_SPECIES</div><div> Mg 24.305 Mg.pw91-np-van.UPF</div><div> O 15.999 O.pw91-van_ak.UPF</div><div>
ATOMIC_POSITIONS</div>
<div> Mg 0.00 0.00 0.00 </div><div> O 0.00 0.00 0.70 </div><div>K_POINTS (automatic)</div><div>3 3 2 0 0 0 </div><div><br clear="all"><br><br>
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