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[Anglade Pierre-Matthieu <anglade@gmail.com>]

Hi,

Except the fact that you have exchanged tolwfr and tolvrs everywhere
in your message I think it sums up correctly what I have writen.

regards

PMA

On Fri, Jun 5, 2009 at 2:31 PM, Zhenhua Zeng<myid520@163.com> wrote:
> Hi PMA, Matthieu,
>
> I think I understand this 'tolerant criterial' post well now.
>
> Although B.W. Dong did not express his/her questions clearly,
> I think what he/she want to ask is why tolwfr is used in GS calcualtions,
> while tolvrs is used in  RF calculation.
>
> Excitinglly, PMA just gave a very excellent explanation: tolwfr in GS for
> a cnvergent density (from a convergent wave function), while tolvrs in
> RF for a convergent potential (fixed density in non-scf).
>
> I know that RF calcualtions start from convergent wave functions from GS
> calculation. Here I want to make sure one thing, i.e. are RF calcualtions
> really non-selfconsistent?  If it is sure non-sc, then the density will
> be determined directly from readed GS wave function, and not update in the
> following non-scf loop (wave function will be update of course).
> Correct me if I'm wrong on above understanding.
>
> I think I need to read the paper PMA mentioned to gain a deeper 
> understanding.
> Whatever, a straight answer is greatly appreciated.
>
> Best Wishes
> Zhenhua Zeng
>
> -------------------------------------------------------------
> From：Anglade Pierre-Matthieu
> sent:：2009-06-05 16:15:07
> To：forum@abinit.org
> Subject：Re: [abinit-forum] tolerant criteria of rf calculations.
>
>>
>>Hi St Druid,
>>
>>I may mistake on the following but this may be part of the answer to
>>your question on convergence criterion :
>>
>>The density functional theory is used to produce a density based
>>ground state. That is to say the result of a DFT calculation is an
>>electronic density, directly related to the potential via Poisson's
>>equation. Therefore, convergence of a ground state calculation is
>>quite adequatly monitored through the change of density or potential
>>along the algorithmic search for self-consistent solution. Then for a
>>ground state calculation, the most straight forward  (and accurate)
>>convergence criterion is based on the change of hartree potential
>>(better than density since potential changes faster and is then less
>>susceptible to numerical errors). It is however mandatory for ground
>>state calculations to check that the wave functions are converged,
>>since in some cases the algorithms may encounter a "sticky" potential
>>that doesn't change (and matches the convergence criterion)
>>eventhough the wavefunction are unconverged, which in turns means that
>>the density is wrong ...
>>
>>For response function calculation, one keeps the ground state (i.e.
>>density) and tries to evaluate the ratio of change of energy with
>>respect to a perturbation of the hamiltonian. In the limits where the
>>perturbation is negligible, the density is unchanged and only the
>>wavefunctions are perturbed to first order (see Phys. Rev. A 52, 1086
>>- 1095 (1995) for an accurate explanation). So response function
>>calculations are non-selfconsistent and consist in evaluation of the
>>response of the wave-function to a perturbation. Therefore, the single
>>accurate convergence criterion for such calculation is the change of
>>wave-functions.
>>
>>Best regards
>>
>>PMA
>>
>>
>>
>>On Fri, Jun 5, 2009 at 9:40 AM, matthieu verstraete
>><matthieu.jean.verstraete@gmail.com> wrote:
>>>> I am just wondering why the scf calculation are different between
>>>> phonon and el-phon.
>>> you attach an abinit input file to calculate phonons (this is fine).
>>> The electron phonon calculation is done later in anaddb.
>>>
>>> I still do not know what you mean by bad convergence etc... The phonon
>>> perturbation calculation is different from a ground state, there is no
>>> reason it should converge the same way, but it should converge...
>>>
>>> Again, please follow _all_ of the nettiquette
>>> http://wwwold.abinit.org/community/?text=netiquette
>>>
>>> Matthieu
>>>
>>>
>>>
>>> --
>>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> Dr. Matthieu Verstraete
>>>
>>> European Theoretical Spectroscopy Facility (ETSF)
>>> Dpto. Fisica de Materiales,
>>> U. del Pais Vasco,
>>> Centro Joxe Mari Korta, Av. de Tolosa, 72,   Phone: +34-943018393
>>> E-20018 Donostia-San Sebastian, Spain        Fax  : +34-943018390
>>>
>>> Mail : matthieu.jean.verstraete@gmail.com
>>> http://www-users.york.ac.uk/~mjv500
>>>
>>>
>>
>>
>>
>>--
>>Pierre-Matthieu Anglade
>>
>>.
> S
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>
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>
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-- 
Pierre-Matthieu Anglade