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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Dear QE users,<br>
<br>
I managed to resolve the issue below by switching from 'vdw-df' to 'vdw-df2'. However, when I compared the binding energy of hydrogen for 'relax' and 'vc-relax', I noticed a considerable difference (vc-relax values were ~40% lower than relax values) in energy
values. In theory, the vc-relax case should be more accurate, but is that a correct assumption or is it more realistic to go with the values obtained from the 'relax' case?<br>
<br>
Best regards,<br>
Janet Wong<br>
Graduate student<br>
University of Toronto, Canada<br>
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<div style="direction: ltr;" id="divRpF67798"><font color="#000000" face="Tahoma" size="2"><b>From:</b> Janet Wong<br>
<b>Sent:</b> Wednesday, June 13, 2012 4:06 PM<br>
<b>To:</b> pw_forum@pwscf.org<br>
<b>Subject:</b> vdw-DF study for calcium decorated graphene<br>
</font><br>
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<div style="direction:ltr; font-family:Tahoma; color:#000000; font-size:10pt">Dear QE users,<br>
<br>
I am currently trying to calculate the adsorption energy of hydrogen on calcium decorated graphene using the van der Waals functional. However, I could not obtain convergence for my system. Prior to this, I calculated the adsorption energy of hydrogen on the
calcium decorated graphene sheet with pbe pseudopotential using the 'relax' calculation. The adsorption energy calculated from this latter case was in agreement with another study conducted on the same system. Then I used the final coordinates of the relaxed
structure, and plugged it into the new input file for the van der Waals functional case and for some reason the calcium atom and the hydrogen molecules moved further away from the graphene sheet and the total energy of the system did not converge. I assumed
that the relaxed structure obtained from the pbe pseudopotential case would have been similar to the relax structure of the van der Waals functional case. But this does not seem to be true according to my output file. Does anyone have any suggestions as to
what I did incorrectly and how I should fix this? Please see below for my input file for the vdW-DF case.<br>
<br>
&control<br>
prefix='6C_2Ca_4H2_30'<br>
calculation='relax'<br>
outdir = './out'<br>
pseudo_dir = '/RQexec/wongjane/graphene/pseudo/'<br>
forc_conv_thr=8D-4,<br>
/<br>
&system<br>
ibrav=4,<br>
celldm(1)=8.0529,<br>
celldm(3)=5.8666,<br>
nat=16, ntyp=3,<br>
ecutwfc=30, ecutrho=300<br>
occupations='smearing', smearing='methfessel-paxton', degauss=0.02<br>
input_dft='vdW-DF',<br>
/<br>
&electrons<br>
mixing_mode='local-TF',<br>
mixing_beta=0.3,<br>
diagonalization='cg',<br>
conv_thr=0.000007,<br>
/<br>
&ions<br>
ion_dynamics='bfgs'<br>
/<br>
ATOMIC_SPECIES<br>
C 12.01 C.pbe-van_bm.UPF<br>
Ca 40.078 Ca.pbe-nsp-van.UPF<br>
H 1.01 H.pbe-van_bm.UPF<br>
ATOMIC_POSITIONS crystal<br>
H 0.170968317 0.296757710 0.354542022<br>
H 0.280193454 0.194532821 0.355976475<br>
H 0.678887709 0.805195324 0.357509777<br>
H 0.781228558 0.696564044 0.358999571<br>
Ca 0.500714949 0.500950804 0.272750072<br>
C 0.829674303 0.498485404 0.179808930<br>
C 0.496741650 0.831404416 0.179746906<br>
C 0.163637826 0.165386133 0.179821371<br>
C 0.163804328 0.498448431 0.179774763<br>
C 0.496730502 0.165514945 0.179840143<br>
C 0.829848249 0.831571577 0.179766791<br>
Ca 0.500677466 0.501116785 0.086856861<br>
H 0.170992960 0.296734966 0.005052814<br>
H 0.280192056 0.194484391 0.003625759<br>
H 0.678910890 0.805180269 0.002106836<br>
H 0.781279186 0.696574936 0.000615775<br>
K_POINTS automatic<br>
8 8 1 1 1 1<br>
<br>
<br>
Thank you all in advance.<br>
<br>
Regards,<br>
Janet Wong<br>
Graduate Student<br>
University of Toronto<br>
Canada</div>
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