[Wien] phonon calculation

[Yundi Quan]

When doing structure minimization, I need to calculate a series of
structures. Is it fine to set different Muffin-Tin sphere for different
calculations. I believe it is fine because I am not comparing them with each
other. Is it?


Yundi

On Thu, Sep 1, 2011 at 12:41 PM, Laurence Marks <L-marks at northwestern.edu>wrote:

> 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 Евгения Каблиман <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 Евгения Каблиман <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
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> >>>>>
> >>>>
> >>>>
> >>>>
> >>>> --
> >>>> 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
> >>>>
> >>>> _______________________________________________
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> >>>>
> >>>
> >>>
> >>> _______________________________________________
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> >>>
> >>
> >>
> >>
> >> --
> >> 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
> >>
> >> _______________________________________________
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> >>
> >
> >
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> >
> >
>
>
>
> --
> 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
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