----------------------------------------
> From: paolo.giannozzi at uniud.it
> To: pw_forum at pwscf.org
> Date: Fri, 25 Apr 2014 03:42:06 +0200
> Subject: Re: [Pw_forum] tpss: too many bands are not converged
>
> On Thu, 2014-04-24 at 09:03 -0400, Mike Marchywka wrote:
>
>> By free volume, you mean places where n and likely grad everything are
>> numerical noise?
>
> exactly: the regions of space where the charge has decayed to noise.
> Apparently (the current implementation of) meta-GGA doesn't like the
> presence of such large regions (and it doesn't seem to like H atoms
> as well). Even plain GGA diverges in those regions: it is less of a
> problem, but still, the exact energy values depend upon how the
Does it actually diverge or just reach some kind of limit cycle with
amplitude in energy greater than convergence criteria? ?
> potential is cut off. The divergence comes from gradient corrections
> to exchange: there is no divergence in atoms with the correct large-r
so this is related to PP and lack of exponential decay giving more weight
to "free volume" than it should physically have? I had been doing some
tests with analytical hydrogen since it was easy to check :) That is not noise
alone then but a modelling issue.?
> limit of the charge density, but this is not of much help in plane-wave
> calculations of condensed-matter systems.
Molecular crystals better or worse than say metals??
>From what I can tell of the TPSS "z" anyway, trying to calculate it
as a ratio of intermediate real quantities seems to allow for many errors
such as aliasing that may occur by taking magnitudes. ?I did some
algebra it looks like the magnitude of the grad of the wf angle is more direct
but I have
not checked the math or tested it much although IIRC some related results
vs analytical hydrogen did not appear obviously wrong but this was hardly a
complete test.
>
> (disclaimer: this is what I remember. I looked at this problem several
> years ago for meta-GGA, many years ago for GGA)
Thanks, I'm just trying to understand a few things and see if I can play with
the problematic terms and evaluate some alternatives.
>
> Paolo
>> AFAICT, the converge of SCF is largely empirical
>> as there does not seem to be much theory here. In any case, you would like
>> to think that the areas lacking "physics" should not be that
>> big a factor in the overall calculation and if that is not the case there
>> may be something interesting here to explore :)
>>
>>> You can try to decrease the size of the unit-cell in order to minimize the
>>> free space it contains. Of course, this will be at the expense of the
>>> inter-polyemer interaction you probably want to avoid.
>>>
>>> Nevertheless, this will probably not cure your problem, which to my
>>> knowledge has no other solution than changing the meta-GGA functional to a
>>> GGA one.
>>
>> I took a look at the "z" parameter which being a ratio could have some issue
>> with small denominators. With some initial work,
>> it looks like there are better ways to calculate it than directly from real
>> quantities such as n and grad mags,
>> but I am still trying to test what may be trivially wrong math :)
>> I think my latest result was something to the effect that you could reduce z
>> to A/(A+B)( both non-negative)
>> if you calculate everything from psi and the grad of psi expressed in polar
>> form, not much different from some formula
>> for current densities, and maybe find a limit when A and B are both zero.
>>
>> I had originally hoped to try to test it for trivial issues in JDFTX and c++
>> or c with libxc using an expanded interface scheme
>> to let me pass z or grad psi in polar form but it will require a bit of
>> effort. Curious if anyone else here has examined
>> this or has literature references they care to share. Seems disconcerting
>> that something with physical meaning would have these
>> kinds of implementation issues - perhaps something else can be learned from
>> investigating.
>>
>> Thanks.
>>
>>> Best regards,
>>>
>>> Yves
>>>
>>>
>>>
>>> Le 24 avr. 2014 ? 13:36, Davide Tiana a ?crit :
>>>
>>>>
>>>> Dear all,
>>>> I've been trying to calculate a polymer using tpss. I already fully
>>>> optimised it with different functional (pbesol, pw91, hse) and
>>>> pseudopotential (nc, paw). For some reason (apologise my ignorance if
>>>> it should be well known) when I try to calculate using tpss nc the
>>>> system simply does not converge crashing with this error:
>>>>
>>>> Error in routine c_bands (1):
>>>> too many bands are not converged
>>>>
>>>> After some reaserch in old pw-forum mails, I tried decreasing
>>>> mixing_beta=0.2, increasing mixing_ndim=12, as well as mixing mode TF
>>>> and local-TF.
>>>> everythings failed.
>>>>
>>>> Does anyone have any tips or idea of why the system can't converge?
>>>>
>>>> Thanks a lot,
>>>> Davide
>>>>
>>>>
>>>>
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>>>
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>
> --
> Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
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