<blockquote style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;" class="gmail_quote"> Izaak Williamson wrote on Tue, 3 May 2011 09:54:14 -0700<br><br>I am trying to calculate the cohesive energy of the N2 molecule using the<br>
attached input file (<a href="http://relax.in/" target="_blank">relax.in</a>) and am getting a value of -16.57 eV. I use DFT<br>
with GGA and the pseudo-potential N.pbe-rrkjus.UPF. Other work [Fuchs et. al.,<br>
Phys. Rev. B 65, (2002)245212] has performed similar calculations and obtained<br>
values ~10.5 eV. They even list an experimental value of 9.76 eV. Why is my<br>
value so much higher? Is there anything in my input file that could be giving<br>
inaccurate results? Is it my pseudo-potential that is causing this problem?<br>
<br>
Thanks for any help.<br>
<br>
--<br>
Izaak Williamson<br>
Research Assistant<br>
Physics Department<br>
Boise State University<br>
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<br><br>Dear Izaak<br><br>Did you considered symmetry for energy calculation of atomic nitrogen or not ? As you know the electronic configuration of atomic nitrogen is 1s[2] 2s[2] 2px[1] 2py[1] 2pz[1] and seems symmetric. In some quantum mechanical codes when one calculates the energy of this system without considering symmetry may get wrong answer since the system may go to a non-symmetric status like 1s[2] 2s[2] 2px[2] 2py[1]. Please calculate the energy with and without symmetry and compare them.<br>
Another important issue is that did you considered polarization of spin (with defining a proper starting magnetization value for nitrogen) in your calculations ? It can cause a significant change in the energy since your system includes unpaired electrons. <br>
Let us know the changes after considering the above issues. I hope it helps. <br><br><br> <div><div style="text-align: center;"><div style="text-align: center;"><font size="1"><span style="font-size: small;"><span><span style="font-size:9pt;line-height:14px;font-family:'Comic Sans MS';color:black">Best Wishes</span></span><span style="font-size: 9pt; line-height: 14px; font-family: 'Comic Sans MS'; color: black;"></span></span></font><br>
<font size="1"><span style="font-size: small;"><span style="font-size: 9pt; line-height: 14px; font-family: 'Comic Sans MS'; color: black;"></span></span></font><br><font size="1"><span style="font-size: small;"><span style="font-size: 9pt; line-height: 14px; font-family: 'Comic Sans MS'; color: black;"><span> Masoud</span></span></span></font><br>
</div><font size="1"><span style="font-size: small;"><span style="font-size: 9pt; line-height: 14px; font-family: 'Comic Sans MS'; color: black;"></span></span></font></div><font size="1"><span style="font-size:small"><span style="font-size:9pt;line-height:14px;font-family:'Comic Sans MS';color:black"><span><br>
--------------</span><br><span>Masoud Nahali, Sharif University of Technology</span></span></span></font></div>
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