Hi,<br><br>I think you may need to increase the k-point mesh for bulk calculation and do the spin-polarized for isolated atom. Another point: the calculated cohesive energy in general depends very much not only on the functional but also the pseudized potential (cutoff radius, configuration...). So one may consider to calculate it with many different available potentials. <br>
<br>Best,<br><br><div class="gmail_quote">On Mon, Aug 31, 2009 at 2:54 PM, Stefano Baroni <span dir="ltr"><<a href="mailto:baroni@sissa.it" target="_blank">baroni@sissa.it</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div>No need to post twice the same message ...<div>Don't now about your specific system, but it is not unusual that DFT overestimate binding energies (less so for PBE than LDA)</div><div>Please, do not forget to sign your posts, including your affiliation</div>
<div>SB</div><div><br><div><div><div></div><div><div>On Aug 31, 2009, at 8:37 PM, udayagiri sai babu wrote:</div><br></div></div><blockquote type="cite"><div><div></div><div>Hi all<br>i am claculating cohesive energy of V using pwscf but i got -8.15 ev/atom against an experimental value of 5.3 ev/atom which is almost 50% off can anybody say what is going wrong with the calculation. the method i used is calculate the total energy of a bcc crystal with 1 atom and deduct the energy of isolated atom from it. the following input files are for finding the total energy for isolated atom and the atom in the crystal. Please tell me if my methodology is wrong.<br>
<br><b>cohesive energy=E per atom (in the crystal)-E per atom (isolated)</b><br><br><b>input file for finding the total energy of an isolated atom</b><br><br>&control<br>calculation = 'scf',<br>restart_mode='from_scratch',<br>
outdir='/home/sai/temp',<br>prefix='vanadium'<br>pseudo_dir='/home/sai/<div>softwares/espresso-4.0.1/pseudo/',<br>tstress = .TRUE.,<br>tprnfor = .TRUE.,<br>/<br>&system<br> ibrav=1<br>celldm(1)=30,<br>
nat=1,<br>ntyp=1<br>ecutwfc=25,<br>ecutrho=100,<br>occupations='smearing',<br>smearing='mv',<br>degauss=0.010000<br>/<br>&electrons<br>conv_thr=1.D-8,<br>diagonalization='david',<br> mixing_mode='plain',<br>
mixing_beta= 0.3<br>/<br>ATOMIC_SPECIES<br>V 50.9415 V.pbe-n-van.UPF<br>ATOMIC_POSITIONS (crystal)<br>V 0.00000000 0.00000000 0.00000000<br>K_POINTS {automatic}<br>1 1 1 0 0 0<br><br><b>input file for finding the total energy of the atom in the crystal</b><br>
<br>&control<br>calculation = 'scf',<br>restart_mode='from_scratch',<br>outdir='/home/sai/temp',<br>prefix='vanadium'<br>pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/',<br>
tstress = .TRUE.,<br>tprnfor = .TRUE.,<br>/<br>&system<br>ibrav=3<br>celldm(1)=5.654,<br>nat=1,<br>ntyp=1<br>ecutwfc=25,<br>ecutrho=100,<br>occupations='smearing',<br>smearing='mv',<br>degauss=0.010000<br>
/<br>&electrons<br>conv_thr=1.D-8,<br>diagonalization='david',<br>mixing_mode='plain',<br>mixing_beta= 0.3<br>/<br>ATOMIC_SPECIES<br>V 50.9415 V.pbe-n-van.UPF<br>ATOMIC_POSITIONS (crystal)<br>V 0.00000000 0.00000000 0.00000000<br>
K_POINTS {automatic}<br>8 8 8 0 0 0</div></div></div> _______________________________________________<br>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org" target="_blank">Pw_forum@pwscf.org</a><br><a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br>
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<div><div style="margin: 0px;"><font size="3"><span style="font-size: 12px;">---</span></font></div><div style="margin: 0px;"><font size="3"><span style="font-size: 12px;">Stefano Baroni - SISSA</span></font><font size="3"><span style="font-size: 12px;"> </span></font><font size="3"><span style="font-size: 12px;">&</span></font><font size="3"><span style="font-size: 12px;"> </span></font><font size="3"><span style="font-size: 12px;">DEMOCRITOS National Simulation Center - Trieste</span></font></div>
<div style="margin: 0px;"><font size="3"><span style="font-size: 12px;"><a href="http://stefano.baroni.me" target="_blank">http://stefano.baroni.me</a> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)</span></font></div>
<div style="margin: 0px; min-height: 14px; font-size: 12px;"><br style="font-size: 12px;"></div><div style="margin: 0px; min-height: 14px; font-size: 12px;"><span style="font-size: 14px;"><div style="margin: 0px;"><font size="3"><span style="font-size: 12px;">La morale est une logique de l'action comme la logique est une morale de la pensée - Jean Piaget</span></font></div>
<div style="margin: 0px;"><font size="3"><span style="font-size: 12px;"><br></span></font></div></span></div><div style="margin: 0px;"><font size="3"><span style="font-size: 12px;">Please, if possible, don't</span></font><font size="3"><span style="font-size: 12px;"> </span></font><font size="3"><span style="font-size: 12px;">send me MS Word or PowerPoint attachments</span></font></div>
<div style="margin: 0px;"><font size="3"><span style="font-size: 12px;">Why? See:</span></font><font size="3"><span style="font-size: 12px;"> </span></font><font color="#0023e9" size="3"><span style="font-size: 12px;"><a href="http://www.gnu.org/philosophy/no-word-attachments.html" target="_blank">http://www.gnu.org/philosophy/no-word-attachments.html</a></span></font></div>
<div><font color="#0023e9" size="3"><span style="font-size: 12px;"><br></span></font></div></div></div></span><br></div></span><br></div></span><br></div></span><br></div></span><br> </div><br></div><br>_______________________________________________<br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>--------------------------------------------------<br>Duy Le<br>PhD Student<br>Department of Physics<br>University of Central Florida.<br>