Thank you for your respond. I just compare the total ground state energy from two output files. I basically created two input files for the one material structure (zinc blend). The calculation is done on 1x1x1 unit cell, so I used all parameters the same for both input file except the ibrav between 0 and 2. On the ibrav=2, then it is simple, I just have to list two atom positions for zinc blend structure (000 and 1/4 1/4 1/4). For the ibrav=0, I have to list 8 atom positions (4 for the fcc lattice and 4 for the tetrahedral sites). lattice parameter is the same, k-point and cutoff energy is also the same. The calculated total energy value I got from ibrav=0 is 4 times higher than that from ibrav=2. I had the idea of why it is the case but I just want to make sure I understand it correctly. So if you find anything wrong on the way i set up my file, please let me know. Please also accept my apology if my question confused you.
Thank you, On Wed, Jan 16, 2013 at 7:13 AM, Duy Le <ttduyle at gmail.com> wrote: > Should you compare total energy per atom or total energy per unit volume? > Of course, you have to use well-converged cutoff and k-point sampling. > ---------------------------------------------------- > Duy Le > Postdoctoral Associate > Department of Physics > University of Central Florida. > Website: http://www.physics.ucf.edu/~dle > > > On Wed, Jan 16, 2013 at 3:25 AM, Lorenzo Paulatto < > lorenzo.paulatto at impmc.upmc.fr> wrote: > >> On 16 January 2013 02:33, Tram Bui <trambui at u.boisestate.edu> wrote: >> >>> Dear QE Users, >>> I ran the calculation for a simple 1x1x1 unit cell SiC (zinc >>> blend structure) . The calculated total energy for when ibrav=2 (two atoms >>> per cell) is different from when ibrav=0 (8 atoms per cell). Would you give >>> me some information on why the total energy changes? >>> >> >> >> Dear Tram, >> maybe you did not use 2 sets of k-points that map perfectly from one >> system to the other. >> >> bests >> >> -- >> Dr. Lorenzo Paulatto >> IdR @ IMPMC -- CNRS & Universit? Paris 6 >> phone: +33 (0)1 44275 084 / skype: paulatz >> www: http://www-int.impmc.upmc.fr/~paulatto/ >> mail: 23-24/4?16 Bo?te courrier 115, 4 place Jussieu 75252 Paris C?dex 05 >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- Tram Bui M.S. Materials Science & Engineering trambui at u.boisestate.edu -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20130118/f3be9086/attachment.html
