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        Greetings, QE users and experts,
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        I try to relax a seven-layer Ir slab <span style="font-family:Arial;white-space:normal;"> at gamma point </span>with 15 Angstrom high vacuum added along z-axis, bottom four layers are fixed and top three layers are allowed to relax. However, after relaxation, I find top two layers almost depart from the bottom five layers. Is there something wrong with my input script? I also perform the same calculation on other elements such as Au, Pt and Pd, but problem only emerges in Ir-system.
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        I attach my input script in the following, any suggestions will be appreciated.
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        -----------------------------------
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        <span style="font-family:Arial;">&CONTROL</span><br>
<span style="font-family:Arial;">calculation = 'relax'</span><br>
<span style="font-family:Arial;">outdir = './Ir7_slab_relax_spin_polarized/'</span><br>
<span style="font-family:Arial;">prefix = 'opt'</span><br>
<span style="font-family:Arial;">pseudo_dir = './'</span><br>
<span style="font-family:Arial;">restart_mode = 'from_scratch'</span><br>
<span style="font-family:Arial;">tprnfor = .TRUE.</span><br>
<span style="font-family:Arial;">wf_collect = .TRUE.</span><br>
<span style="font-family:Arial;">/</span><br>
<span style="font-family:Arial;"><br>
</span><br>
<span style="font-family:Arial;">&SYSTEM</span><br>
<span style="font-family:Arial;">degauss = 0.002</span><br>
<span style="font-family:Arial;">ecutwfc = 60</span>
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        ecutrho = 600<br>
<span style="font-family:Arial;">ibrav = 0</span><br>
<span style="font-family:Arial;">nat = 7</span><br>
<span style="font-family:Arial;">ntyp = 1</span><br>
<span style="font-family:Arial;">occupations = 'smearing'</span><br>
<span style="font-family:Arial;">/</span><br>
<span style="font-family:Arial;"><br>
</span><br>
<span style="font-family:Arial;">&ELECTRONS</span><br>
<span style="font-family:Arial;">electron_maxstep = 100</span><br>
<span style="font-family:Arial;">mixing_beta = 0.5</span><br>
<span style="font-family:Arial;">scf_must_converge = .TRUE.</span><br>
<span style="font-family:Arial;">/</span><br>
<span style="font-family:Arial;"><br>
</span><br>
<span style="font-family:Arial;">ATOMIC_SPECIES</span><br>
<span style="font-family:Arial;">Ir 192.22 Ir_pbe_v1.2.uspp.F.UPF</span><br>
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</span><br>
<span style="font-family:Arial;">K_POINTS {GAMMA}</span><br>
<span style="font-family:Arial;"><br>
</span><br>
<span style="font-family:Arial;">CELL_PARAMETERS {angstrom}</span><br>
<span style="font-family:Arial;">2.7351000000 0.0000000000 0.0000000000</span><br>
<span style="font-family:Arial;">-1.3675500000 2.3686660819 0.0000000000</span><br>
<span style="font-family:Arial;">0.0000000000 0.0000000000 28.3994000000</span><br>
<span style="font-family:Arial;"><br>
</span><br>
<span style="font-family:Arial;">ATOMIC_POSITIONS {angstrom}</span><br>
<span style="font-family:Arial;">Ir 0 0 0 0 0 0</span><br>
<span style="font-family:Arial;">Ir 1.3675636755 0.789547465077 2.233328816 0 0 0</span><br>
<span style="font-family:Arial;">Ir -1.36754999994e-05 1.57911861681 4.466373638 0 0 0</span><br>
<span style="font-family:Arial;">Ir 0 0 6.699702454 0 0 0</span><br>
<span style="font-family:Arial;">Ir 1.3675636755 0.789547465077 8.93303127</span><br>
<span style="font-family:Arial;">Ir -1.36754999994e-05 1.57911861681 11.166076092</span><br>
<span style="font-family:Arial;">Ir 0 0 13.399404908</span> 
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        Yike Huang, PhD candidate.
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        Dalian Institute of Chemical Physics, CAS, China.
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