[Wien] phonon calculation

[Yundi Quan]

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
>>>>
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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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> Wien mailing list
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>
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