Thanks for you reply. My minimization stops with a message saying that the force is minimized and the force and energy are inconsistent. So I carried out another calculation by using the structure file that I got. However, the force on one of the atoms is as large as 26. Is it too large to be used as a equilibrium state? Thanks a lot.
Yundi 2011/8/31 ??????? ???????? <evgeniya at theochem.tuwien.ac.at> > I mean minimization of internal parameters (lattice coordinates) in your > initial structure. This is a crucial point. You should not have forces on > atoms, since it is a kind of reference state. The structure optimization > (lattice parameters) itself is less crucial as long as you have the > reasonable lattice parameters. > > Once you have a well relaxed structure, you can construct atomic > displacements and calculate 'total forces' using force convergence criteria > (-fc) at fixed lattice constants. > > Total forces, which you need for phonon calculations, are the derivatives > of total energies with respect to atomic displacements. Therefore, in order > to get more precise values of total forces one usually constructs big > supercells. This means that a size of your supercell is also important. > > > > 2011/8/31 Yundi Quan <quanyundi at gmail.com> > >> By relaxing structure, do you mean internal structure or the crystal >> structure or both? >> >> Yundi >> >> >> 2011/8/31 ??????? ???????? <evgeniya at theochem.tuwien.ac.at> >> >>> Fisrt you have to relax your structure until you have no forces on all >>> your atoms. Then you create the displacements and perform scf calculations >>> without minimization. >>> >>> 2011/8/31 Yundi Quan <quanyundi at gmail.com> >>> >>>> Hi, When doing phonon calculation, do I have to do structure >>>> minimization first? >>>> >>>> Yundi >>>> >>>> _______________________________________________ >>>> Wien mailing list >>>> Wien at zeus.theochem.tuwien.ac.at >>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >>>> >>>> >>> >>> >>> -- >>> Evgeniya Kabliman. >>> Insitute of Materials Chemistry Vienna University of Technology >>> Getreidemarkt 9/165-TC, A-1060 Vienna, Austria >>> Tel: +43 1 58801 15674 Fax: +43 1 58801 15698 >>> evgeniya at theochem.tuwien.ac.at http://www.imc.tuwien.ac.at >>> >>> _______________________________________________ >>> Wien mailing list >>> Wien at zeus.theochem.tuwien.ac.at >>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >>> >>> >> >> _______________________________________________ >> Wien mailing list >> Wien at zeus.theochem.tuwien.ac.at >> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >> >> > > > -- > Evgeniya Kabliman. > Insitute of Materials Chemistry Vienna University of Technology > Getreidemarkt 9/165-TC, A-1060 Vienna, Austria > Tel: +43 1 58801 15674 Fax: +43 1 58801 15698 > evgeniya at theochem.tuwien.ac.at http://www.imc.tuwien.ac.at > > _______________________________________________ > Wien mailing list > Wien at zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20110901/f94e5aba/attachment.htm>