> > Izaak Williamson wrote on Tue, 3 May 2011 09:54:14 -0700 > > I am trying to calculate the cohesive energy of the N2 molecule using the > attached input file (relax.in) and am getting a value of -16.57 eV. I use > DFT > with GGA and the pseudo-potential N.pbe-rrkjus.UPF. Other work [Fuchs et. > al., > Phys. Rev. B 65, (2002)245212] has performed similar calculations and > obtained > values ~10.5 eV. They even list an experimental value of 9.76 eV. Why is my > value so much higher? Is there anything in my input file that could be > giving > inaccurate results? Is it my pseudo-potential that is causing this problem? > > Thanks for any help. > > -- > Izaak Williamson > Research Assistant > Physics Department > Boise State University > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > http://www.democritos.it/pipermail/pw_forum/attachments/20110503/9e728584/attachment.htm > -------------- next part -------------- > A non-text attachment was scrubbed... > Name: relax.in > Type: application/octet-stream > Size: 662 bytes > Desc: not available > Url : > http://www.democritos.it/pipermail/pw_forum/attachments/20110503/9e728584/attachment.obj >
Dear Izaak 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. 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. Let us know the changes after considering the above issues. I hope it helps. Best Wishes Masoud -------------- Masoud Nahali, Sharif University of Technology > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110503/aa8d1a4d/attachment.htm
