Yes, much to large. Read the FAQ on minimization, you are doing something wrong.
2011/9/1 Yundi Quan <quanyundi at gmail.com>: > 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 >> > > > _______________________________________________ > Wien mailing list > Wien at zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > > -- Laurence Marks Department of Materials Science and Engineering MSE Rm 2036 Cook Hall 2220 N Campus Drive Northwestern University Evanston, IL 60208, USA Tel: (847) 491-3996 Fax: (847) 491-7820 email: L-marks at northwestern dot edu Web: www.numis.northwestern.edu Research is to see what everybody else has seen, and to think what nobody else has thought Albert Szent-Gyorgi
