On May 9, 2011, at 5:36 AM, swapnil chandratre wrote: > Hi, I have prepared an input file for a porous graphene nanoribbon, can > anyone please comment if there are any errors with the file.
it is always a good idea to open the input file using XCrysDen (or any other visualization software with a working Quantum-ESPRESSO interface), because this often helps in pointing out "structural" (cell paramenters and/or atomic positions) issues (see below). > ecutwfc=80.0 > ecutrho = 600.0 ..... > C 12.0000 C.pz-rrkjus.UPF > H 1.00000 H.pz-rrkjus.UPF > because your pseudos are ultrasoft a 80 Ry cutoff is likely very huge, you can reach convergence with much lower values, I think. Concerning the structural part, there is a problem for sure. > CELL_PARAMETERS > 19.200000 0.000000 0.000000 > 0.0000000 21.90350 0.000000 > 0.0000000 0.000000 10.00000 you chose an orthorombic unit cell with axis lengths of about 10, 11.4 and 5,0 Angstrom, respectively. But if you look at the atomic positions, you can easily see that: > C 0.710430 9.644997 5.000000 > H 20.44254 5.000000 5.000000 the x coordinates of these two atoms differ by 20.4 - 0.7 = 19.7 A which is less than your unit cell size along the x axis. The mistake probably originates from the fact that if you DO NOT specify celldm(1), the units of coordinates within the CELL_PARAMETERS card is a.u., namely, Bohr. I guess that you want to specify those units in Angstrom, indeed, the structure looks much better (with a hole that is what you mean with "porous") if you set celldm(1)=1.889727 (inverse of Bohr). Anyway, orthorombic cells are much easier specified by setting ibrav=8 and then a, b, c as axis lengths in Angstrom (see Doc/INPUT_PW.txt). Even after correctly specifying axis length units there is still a problem with the above atoms, because the 19.7 A difference of x coordinates is still larger than the 19.2 Angstrom a-axis. So, either the atomic positions are wrong, or the cell size was incorrectly computed. Giovanni -- **** PLEASE NOTICE THE NEW E-MAIL ADDRESS: giovanni.cantele at spin.cnr.it Giovanni Cantele, PhD CNR-SPIN and Dipartimento di Scienze Fisiche Universita' di Napoli "Federico II" Complesso Universitario M. S. Angelo - Ed. 6 Via Cintia, I-80126, Napoli, Italy Phone: +39 081 676910 - Fax: +39 081 676346 Skype contact: giocan74 ResearcherID: http://www.researcherid.com/rid/A-1951-2009 Web page: http://people.na.infn.it/~cantele http://www.nanomat.unina.it -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110509/7d765035/attachment.htm
