Dear PWSCF community In my study I got a problem which I can't solve by myself, unfortunately. I hope you can give me some tips where I made a mistake. I have to to investigate the energy difference between graphite and diamond, but I can't get trusted result.First of all, I used LDA PP (PZ), I tested it by subsequently increasing of energy cutoff (from 30 Ry to 120 Ry) as well as increasing of k-points mesh (4x4x1 for graphite, 4x4x4 for diamond; 6x6x2 for graphite, 6x6x6 for diamond; 8x8x3 for graphite, 8x8x8 for diamond; 10x10x4 for graphite, 10x10x10 for diamond). I got the difference between energies of diamond and graphite and tried to understand it trend (please, see attached figure). As you can see from the figure difference between energy diamond and graphite is almost zero so I can't say with confidence what structure is more favorable. This result different from other theoretical and experimental studies, therefore it seems that I did something wrong...
My result: ~ 0.001?0.001 eV/atom _______________________________________________ | Energy difference (eV/atom) | Method | Reference | | 0.03 |Experiment | PRB29_6996 | | 0.01 | LDA-PP | PRB29_6996 | | 0.04 | LDA-PP | PRB54_14994| ----------------------------------------------------------------------------------- Input files for diamond and graphite are attached to the letter. -- Sincerely yours *Alexander G. Kvashnin* -------------------------------------------------------------------------------------------------------------------------------- First year of master degree study Moscow Institute of Physics and Technology http://mipt.ru/ 141700, Institutsky lane 9, Dolgoprudny, Moscow Region, Russia Junior research scientist Technological Institute for Superhard and Novel Carbon Materials http://www.ntcstm.troitsk.ru/ 142190, Central'naya St. 7a, Troitsk, Moscow Region, Russia ================================================================ -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110506/a1b4ce06/attachment.htm -------------- next part -------------- A non-text attachment was scrubbed... Name: input_diamond.opt Type: application/octet-stream Size: 1047 bytes Desc: not available Url : http://www.democritos.it/pipermail/pw_forum/attachments/20110506/a1b4ce06/attachment.obj -------------- next part -------------- A non-text attachment was scrubbed... Name: input_graphite.opt Type: application/octet-stream Size: 1113 bytes Desc: not available Url : http://www.democritos.it/pipermail/pw_forum/attachments/20110506/a1b4ce06/attachment-0001.obj -------------- next part -------------- A non-text attachment was scrubbed... Name: Energy_difference.GIF Type: image/gif Size: 10172 bytes Desc: not available Url : http://www.democritos.it/pipermail/pw_forum/attachments/20110506/a1b4ce06/attachment.gif
