[gpaw-users] Convergence issue with mBEEF

[Jens Jørgen Mortensen]

On 11/25/2014 10:44 PM, Jess Wellendorff wrote:
> Marcin: The mBEEf functional was fitted on PBEsol electron densities 
> obtained using rather tight SCF criteria. I think something else must 
> be the root cause of this issue. Perhaps GPAW does not supply LibXC 
> with sufficiently accurate kinetic energy densities?
>
> Monish: Honestly, I believe the only solution to your problem is to 
> lower the SCF convergence criteria, perhaps even completely eliminate 
> them for the eigenstates and rely only on density and energy criteria. 
> I have successfully used this approach. It is not pretty, but it works :)
>
> If you take a look at the mBEEF test script (gpaw/test/mbeef.py), the 
> SCF criteria for very quick molecular calculatios are set to 
> {'eigenstates':1.e+2, 'density':1.e-2, 'energy':1.e-4}. These are 
> bullet-proof settings for a simple test. In general, the density and 
> energy criteria can probably be tightened more. Also, I would expect 
> the eigenstate issue to be much less pronounced in bulk calculations.

What is it that makes mBEEF so special?  I'm struggling with a test 
calculation for a nitrogen atom (not mBEEF, but mBEEF-vdW) and I can 
also not converge the eigenstates.  Strange thing is that TPSS works fine.

It helped a bit to use eigensolver='rmm-diis'.

Jens Jørgen

>
> Hope this helps.
> Best,
> Jess
>
> On 11/25/2014 06:53 PM, Marcin Dulak wrote:
>> On 11/25/2014 04:37 PM, Wellendorff, Jess wrote:
>>> Hi Monish, in my experience, the eigenstates can be hard to converge 
>>> with metagga. Is this your problem?
>> i remember even with the older BEEF-vdW molecules are hard to converge.
>> Maybe this is due to loose SCF thresholds used when fitting the 
>> functional (was it the case also for mBEEF?),
>> so the resulting functional by design is not reaching a tight 
>> convergence.
>>
>> Best regards,
>>
>> Marcin
>>>
>>> Best,
>>> Jess
>>>
>>>
>>>> On Nov 25, 2014, at 14:48, mohnish pandey <mohnish.iitk at gmail.com> 
>>>> wrote:
>>>>
>>>> Dear all,
>>>>
>>>> I am trying to do some test calculations with mBEEF functional for 
>>>> some solids like ZnO. But I am facing difficulty in converging the 
>>>> calculations. I tried tweaking mixing, Fermi temperature etc, but 
>>>> it didn't help. Would really appreciate if somebody helps me out 
>>>> with the issue. Thanks a lot in advance.
>>>>
>>>> -- 
>>>> Regards,
>>>> Mohnish,
>>>> -----------------------------------------------------------------
>>>> Mohnish Pandey,
>>>> PhD Student,
>>>> Center for Atomic-scale Materials Design,
>>>> Department of Physics,
>>>> Technical University of Denmark
>>>> -----------------------------------------------------------------
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>>
>>
>
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