[Wien] phonon calculation

[Laurence Marks]

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
>>>>> Wien at zeus.theochem.tuwien.ac.at
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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
>>>>
>>>> _______________________________________________
>>>> Wien mailing list
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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
>>
>> _______________________________________________
>> Wien mailing list
>> Wien at zeus.theochem.tuwien.ac.at
>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>
>
>
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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