Hi Meenakshi,<br><br>Perhaps it's not converging because some other parameter's error is larger than the wfc one. To check it out, you could try this:<br><br>ecutwfc=50; ecutrho=500 (which are not very high neither very low)<br>
<br>and now check the convergence with respect to:<br>a) degauss value;<br>b) k-points<br>c) number of bands (try with bands = 40 once just to be sure).<br><br>That said, one thing that is not clear to me: when you built that table, you have changed the value of ecutwfc. But for each ecutwfc, did you recalculate the ecutrho so that ecutrho = 8-12 * ecutwfc on each calculation?<br>
<br>Regards,<br><br clear="all">Giovani Faccin<br>UFMS / Brazil<br>
<br><br><div class="gmail_quote">2012/7/5 MMS <span dir="ltr"><<a href="mailto:mm2422@cornell.edu" target="_blank">mm2422@cornell.edu</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi,<br><br>I am trying to simulate bulk Mg in the hcp structure. Before beginning my structural relaxation I wanted to test convergence of the energy values with respect to ecutwfc. This is one of the input files. <br><br>
&control<br> calculation='scf'<br> title='Mgscf'<br> verbosity='high'<br> restart_mode='from_scratch'<br> prefix='Mg'<br> tstress=.true.<br>
tprnfor=.true.<br> pseudo_dir='./pseudo/'<br> outdir='./'<br>/<br>&system<br> ibrav=4<br> celldm(1)=6.0<br> celldm(3)=1.623<br> nat=2<br> ntyp=1<br>
nbnd=10<br> ecutwfc=30<br> ecutrho=240<br> occupations='smearing'<br> degauss=0.015<br> smearing='mv'<br>/<br>&electrons<br> diagonalization='david'<br>
mixing_mode='plain'<br> mixing_beta=0.7<br> conv_thr=1.0D-9<br>/<br>ATOMIC_SPECIES<br>Mg 24.305 Mg.pz-n-vbc.UPF<br>ATOMIC_POSITIONS {crystal}<br>Mg 1/3 2/3 1/4<br>Mg 2/3 1/3 3/4<br>K_POINTS {automatic}<br>
6 6 4 0 0 0<br><br>I kept varying ecutwfc, and ecutrho was parametrized to be eight times ecutwfc. I had used the perdew-zunger LDA pseudopotential. <br><br>Now the ecutwfc values versus the energy values in Rydberg are shown below<br>
20 -4.28664244<br>30 -4.28693764<br>40 -4.28699724<br>50 -4.28701233<br>60 -4.28704753<br>70 -4.28717529<br>80 -4.28739243<br>90 -4.28771080<br>100 -4.28803666<br>110 -4.28853887<br>120 -4.28941450<br>130 -4.28990855<br>
140 -4.29054764<br>
150 -4.29142411<br>160 -4.29309040<br><br>What I notice is that the change in energy values (different between successive values) initially start decreasing, but slowly start increasing and oscillating but always positive, meaning that the energy was continually decreasing. This doesnot help me conclude ecutwfc's convergence point.<br>
<br>Now, I tried varying the degauss values and even tried increasing the k points, but I still see the same behavior. Can I get some pointers in this regard?<br><br>Meenakshi Sundaram<br>Graduate Student<br>Mechanical and Aerospace Engg.<br>
Cornell<a name="138589fa063de67e_smearing"></a>
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<br></blockquote></div><br>