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["Zhenhua Zeng" <myid520@163.com>]

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

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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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